audiolab

assets for the IDM / BxmC audio lab (2MTC, rooms 823/824)

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IDM Serge Synthesizers

Serge System Overview

Serge Modular System in use

Serge synthesizers are analog modular synthesizers based on the designs of Serge Tcherepnin. Tcherepnin, while working at CalArts in the 1970s, developed his line of synthesizers after meeting with Don Buchla and working with composer Morton Subotnick. Tcherepnin realized that modular synthesizers available at the time were far too expensive to be affordable for students and hobbyists, and so he set out to develop a modular system that was low cost and emphasized flexibility. Working with a team of CalArts students, including Rich Gold, Randy Cohen, and Rex Probe, the first Serge systems were built in Tcherepnin’s home in 1973. Tcherepnin made a number of innovative decisions to keep costs down, such as the use of (cheaper) banana jacks instead of audio connectors, and the “paperfacing” of his synthesizer panels so that the aluminum could be pre-drilled in a grid regardless of the customer’s desired module configuration.

In addition, unlike his competitors, Tcherepnin also sold his systems as kits, where the customer would receive a circuit board, a face plate and decal label, a Ziploc bag of discrete electronic components, and detailed assembly instructions. This DIY approach - similar to HeathKit radios popular at the time - allowed Serge synthesizers to be purchased for a fraction of the cost of a Buchla system if the buyer didn’t mind doing some soldering. Many licensed Serge systems today are still sold as kits, with a number of builders, such as our friends at Patch Point in Berlin and Low-Gain Electronics in Minneapolis available to professionaly assemble the kits into finished synthesizers using high quality components.

Tcherepnin’s designs found commercial success as a low-cost alternative to other modular synthesis systems available at the time. His company (Serge Modular Music Systems) sold synthesizers under the Serge name until 1986. Tcherepnin then licensed his designs non-exclusively to a number of manufacturers, such as Sound Transform Systems in the USA (the corporate successor to SMMS, run by Tcherepnin’s former student and employee Rex Probe), Elby Designs in Australia, Random*Source in Germany, the Human Comparator in Sweden, and Loudest Warning in the UK. In addition, a number of synthesizer designers, such as Bugbrand, Modcan, Ciat-Lonbarde, and Kilpatrick Audio, continue to develop new synths using a Serge-inspired or Serge-compatible format.

The Serge-Fans web page (which doubles as an information site for Sound Transform Systems) is a great resource to learn more about the history of these synthesizers.

Ken Stone’s Serge Modular site is another great resource, containing links to original manuals, price lists, circuit descriptions, and panel art.

In addition, there’s a nice video interview by Waveshaper Media with Tcherepnin here.

A scan of a 1976 manual for the Serge synthesizers, written by Rich Gold, Darrel Johansen, and Marina LaPalma, can be found here.

What makes a Serge a Serge?

Serge synthesizers have a number of technical characteristics that set them apart from other modular systems of their day, as well as modern modular synthesizers that use the Eurorack format:

* Form factor trivia: unlike the Eurorack standard - which was developed largely to address issues like this - there’s no standard form factor / power connector / electrical supply standard for 4U synthesizers. Buchla (and the few third-party manufacturers of Buchla clones and new Buchla-compatible modules) make fairly interoperable equipment that is distinct from Serge-style systems, which have themselves diverged in the years since Tcherepnin began licensing designs to other manufacturers in 1986. The R*S modules we use in the IDM analog studio are designed to be compatible (more-or-less) with “original” Serge equipment (including modules made by Sound Transform Systems), but other Serge-style designs vary. Charlie Kerr (the designer of the Loudest Warning Serge-style modules) has a specification that is popular with an increasing number of other 4U designers, but this is far from universal, and commercial 4U manufacturers such as Kilpatrick Audio have created their own specifications.

In terms of overall design, Serge modular systems are considered, alongside Buchla, to be classic “West Coast” synthesizers:

Interface standards

Serge synthesizers are made up of modules that are 4U (7”) tall and multiples of 1” wide. Most (but not all) Serge systems group modules into a single, full rack-width aluminum face (called a “panel”), usually housed in an enclosure (often refered to as a “boat”). Each panel contains up to 16 inches worth of modules and has a single power connector on the rear. The separation between individual modules on a panel is indicated by the panel graphics, usually with a module’s name at the top or bottom, and a visual indicator such as a black rounded rectangle or a gap in the decal around the module.

Serge individual module photo

Modules may have inputs, outputs, or both, depending on their function. In general, outputs on Serge synthesizers appear above and/or to the right of the inputs, and are usually visually indicated on the panel graphics. In the image above, the lower portion of the module (where the knobs are) contain the inputs, while the upper area (bounded by a rectangle) contain the output jacks.

Interface elements on Serge modules consist of jacks (points of connection), LEDs, knobs, toggle switches, push buttons, and, on the TKB module, capacitive touch strips. Interface elements are usually labeled.

Jacks are colored based on the type of voltage they send (or expect to receive). Tcherepnin’s original design called for three types of voltage connection with color codes:

Voltage Type Description Voltage Range Jack Color
AC Bipolar continuous (analog) -2.5V to 2.5V Black or Brown
DC Unipolar continuous (analog) 0 to 5V Blue or Gray
Pulse * Unipolar discrete (digital) 0 or 5V Red

* Serge “Pulse” jacks send and receive more than pulses - a better way to think of them is as “digital”, “binary”, or “boolean” signals, insofar as their voltage state is either HIGH (5V) or LOW (0V). Pulse jacks are used for gates, PWM / square waves, comparator / switching signals, as well as pulses.

Some modules have additional colors, such as lavender jacks for passive connectors on the 73-75 Adapter module and orange for the AC-coupled (-5V or 5V) comparator jack on the Random*Source Smooth / Stepped Generator module. Elby Designs (a licensed Serge manufacturer in Australia) uses an additional set of colors to specify inputs versus outputs, with the standard Serge colors of black, blue, and red being used for input jacks, while white, green, and yellow are used for the corresponding outputs.

As noted above, these conventions describe the kind of voltage being delivered, not how you’re going to use it. In the image above, the output area of the module has black, blue, and red jacks, but all of them can be used to generate either audio patched into the speakers or control voltage patched into another module.

Patching the output of a module delivering one type of voltage into a module jack that expects a different type can have unpredictable results. In general, patching a DC (blue/gray) jack into an AC (black/brown) jack will work as expected, though some modules (such as the Mixer) are designed to only modify signals in the audio range, so a slow-moving DC signal may end up getting filtered out. Patching an AC (black/brown) source into a DC (blue/gray) destination may have unusual results - the negative voltage in the signal may end up getting clipped to 0V or rectified (flipped into positive voltage). Modules with pulse (red) destinations will “fire” when an incoming AC or DC voltage source crosses above 2.5V or so, but processing voltage from a pulse (red) source through a DC or AC processing module may transform the signal in a way that eliminates its ability to trigger anything.

Serge modules use small knobs to control parameters, often in conjunction with control voltage. Knobs that scale (multiply) an input voltage and knobs that offset (add to) an input voltage are distinguished on the panel graphics. Serge scalar knobs are usually bipolar and can apply negative scaling by moving the knob to the left. The zero (12 o’clock) position scales the incoming voltage to 0.

Serge modules that work with frequency as a parameter (oscillators, filters, slope generators) often have CV inputs for both linear frequency (scaled by a knob) and 1 volt-per-octave standard control voltage, allowing the module to be accurately tuned and played by, e.g. a MIDI-to-CV converter.

Modules are connected by patching within and between module jacks using banana cables.

Serge modules patched together

Banana cables can be stacked by inserting one cable into the back or side of another. The cables in the IDM Audio Lab are stored against the wall in the analog studio area, and are color-coded by length.

Banana patch cables

In addition, a box labeled “shorting bars!!!” contain small plastic blocks with two banana connectors that can be used to connect two adjacent jacks on most Serge modules.

Box of shorting bars

As mentioned above, patching using banana jacks means that you’re only connecting the positive (+) end of the audio signal. The negative (-) signals are fed among the sythesizers using common grounding wires. In the analog studio, these are visible as gray banana cables strung around the backs (and sometimes the front) of the equipment. These cables ground the modular synthesizers, the patchbay to the 8A audio interface, the format converter boxes, and the oscilloscopes together.

Grounding cable on the rear of the Shelfisizer

Do not remove or re-plug ground wires - this may prevent the equipment from working properly.

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Random Source Serge

Random\*Source Serge system Random\*Source Serge Panel 5

The Random*Source Serge was built for IDM in 2018-2019 by Darrin Wiener at Patch Point in Berlin. It’s currently configured with four R*S “shop” panels (prebuilt configurations of modules) in a custom zebrawood rack case: a La Bestia II, an Edelweiss II, a Mantra, and a TKB (Touch Activated Keyboard Sequencer). There is also one custom panel of individual modules (“Panel 5”) housed in a separate rack. These panels incorporate many of the module designs sold by Serge Modular Music Systems prior to Tcherepnin’s exit from the company in 1986, with a number of innovations by Random*Source and custom modifications for IDM by Darrin and his colleagues.

Panel 1 (La Bestia II)

Random\*Source La Bestia II

New Timbral Oscillator

The New Timbral Oscillator (NTO) first appeared in 1976, and was (along with a simpler module called the “Precision VCO”) the closest thing Tcherepnin designed to an East Coast-style Voltage Controlled Oscillator.

NTO

  1. Rising sawtooth wave (DC OUTPUT)
  2. Triangle wave (DC OUTPUT)
  3. Sine wave (AC OUTPUT)
  4. Variable waveform, controlled by 6, 9, 12 (AC OUTPUT)
  5. Square wave / pulse (labeled “Puls”) (Pulse OUTPUT)
  6. CV to control the “variable” waveform of 4 (sums with 12) (DC INPUT)
  7. First 1V/Oct CV of oscillator frequency (sums with 8, 18 x 19, 20, and 21) (DC INPUT)
  8. Second 1V/Oct CV of oscillator frequency (sums with 7, 18 x 19, 20, and 21) (DC INPUT)
  9. Scaling knob for 6
  10. Linear FM “Modulator” signal (AC INPUT)
  11. First “Portamento” (frequency slew limiter) CV (sums with 14 and 17) (DC INPUT)
  12. Adjustment for “variable” waveform of 4 (sums with 6 x 9)
  13. CV to control the amount of linear FM 10 (sums with 16) (DC INPUT)
  14. Second Portamento CV (sums with 11 and 17) (DC INPUT)
  15. Oscillator Sync signal for Saw Output 1 (DC INPUT, triggers at 2.5V).
  16. Manual control of the amount of linear FM 10 (sums with 13)
  17. Manual Portamento control (sums with 11 and 14)
  18. Linear frequency CV input (scaled by 19, sums with 7, 8, 20, and 21) (DC INPUT)
  19. Scaling knob for 18
  20. Fine tuning knob for the VCO’s base frequency (sums with 7, 8, 18 x 19, and 21)
  21. Coarse tuning knob for the VCO’s base frequency (sums with 7, 8, 18 x 19, and 20)

Notes:

Mixer

The Mixer is a utility module that allows you to mix up to three AC sources to a single output using a high quality operational amplifier developed by NJR. The mixer is AC-coupled, so it will filter out static (and slow-moving) voltages. The DC-coupled version is called the “Control Voltage Processor”.

Mixer

  1. Mixed signal (AC OUTPUT)
  2. Phase switch for first input (IN 1)
  3. First mixer input (AC INPUT)
  4. Second mixer input (AC INPUT)
  5. Third mixer input (AC INPUT)
  6. Scaling knob for 3
  7. Scaling knob for 4
  8. Scaling knob for 5

Notes:

Wave Multipliers

The Wave Multipliers module appeared in 1976 and is considered an important circuit for achieving the “West Coast” sound of the Serge modular. The module contains three self-contained distortion effects that work by shaping the amplitude of the incoming audio signal. Quoting from the 1982 Serge catalog, Tcherepnin describes the three Wave Multipliers:

The uppermost section is the simplest of the three multiplier sections. but it has two switchable effects. With the switch set at the “HI” position, the module functions to “square-up” an incoming signal. This is not the same as a simple comparator squaring function, though, since there is a rounded flattening of the signal peaks: an effect somewhat similar to overdriving a tube amplifier (except that in this version the process is voltage controllable!). With the switch in the “LO” position, the module is a linear gain controlled VCA. This is useful for various functions such as amplitude modulation and for gating signals into the other sections.

The middle Wave Multiplier provides a sweep of the odd harmonics (1, 3, 5, 7, 9, 11 and 13th) when a sine wave is applied to its input and the knob is turned up or a control voltage is swept from low to high. This effect is similar to overblowing a wind pipe closed at one end, and thus the module can be used to produce the sounds of various wind instruments. A second input is included to allow two signals to be mixed before processing, a technique that we have found to be very usable. This module can be used to explore timbral areas beyond the range of ring modulation because there are more varied harmonics than the sum and difference tones.

The bottom Wave Multiplier performs non-linear wavehaping known as full-wave rectification, but with sophisticated level- compensating conditioning as well. Actually the circuit uses three full-wave rectifier sections linked in a very refined controllable format. Each section can double the frequency of a sine or triangle wave applied to its input. Thus sweeping the VC input over its range will produce a smooth timbral transition using the even harmonics (second, fourth, and eighth). Many other partials are present in this basic sound, however, and the sonorities are very rich and varied. A notable feature of this multiplier is that the full-wave rectification is not accompanied by a reduction in the output amplitude. There is no alteration of the essential level of the sound. There are two inputs to provide mixing before processing, and two outputs. One output is a “squared up” version of the other. This output resembles voltage controlled pulse width modulation (only much more interesting).

Wave Multipliers

  1. CV input for Multiplier 1 amount (DC INPUT)
  2. Processed output of Multiplier 1 (AC OUTPUT)
  3. Scaling knob for Multiplier 1 amount
  4. Signal input for Multiplier 1 (AC INPUT)
  5. High/Low distortion switch for Multiplier 1
  6. Processed output of Multiplier 2 (AC OUTPUT)
  7. CV input for Multiplier 2 amount (DC INPUT)
  8. Second signal input for Multiplier 2 (DC INPUT)
  9. Scaling knob for Multiplier 2 amount
  10. First signal input for Multiplier 2 (AC INPUT)
  11. Second processed (“squared-up”) output for Multiplier 3 (DC OUTPUT)
  12. First processed output for Multiplier 3 (AC OUTPUT)
  13. CV input for Multiplier 2 amount (DC INPUT)
  14. Second signal input for Multiplier 3 (AC INPUT)
  15. Scaling knob for Multiplier 3 amount
  16. First signal input for Multiplier 3 (AC INPUT)

Notes:

Smooth / Stepped Generator #1

The Smooth / Stepped Generator (SSG) was designed by Tcherepnin in 1974. Along with the Dual Universal Slope Generator, it’s one of the most versatile circuits in the canonical Serge system. Depending on how an SSG is patched, it can function as a slew limiter (envelope follower / lowpass filter), a sample-and-hold circuit, a triangle wave oscillator, or a low-pass gate. When combined with its sidecar Noise Source - a small circuit of three jacks - the SSG can be used to develop a wide variety of fluctuating and quantized random voltages, similar to the Buchla 266 Source of Uncertainty.

The module is divided into two halves: the “Smooth” side at the top, and the “Stepped” at the bottom. In between the two, a Coupler circuit outputs a comparator voltage of the two sides. The sidecar Noise Source provides three different types of random sources to work with, either with the SSG or with other modules in the system.

SSG

  1. CV input for the Smooth sides’s rate (DC INPUT)
  2. CV output for the Smooth side (DC OUTPUT)
  3. Scaling knob for 1
  4. Cycle trigger (sends a pulse at the end of a cycle set by the Smooth rate) (Pulse OUTPUT)
  5. Knob for Smooth rate amount (sums with 1 x 3)
  6. Signal input for the Smooth side (AC INPUT)
  7. Hold jack - when set high, Smooth output 2 will freeze and no longer track the module’s input (Pulse INPUT)
  8. Sample jack - when set high, Stepped output 14 will sample and hold Stepped input 10 (Pulse INPUT)
  9. CV input for the Stepped side’s rate (DC INPUT)
  10. Signal input for the Stepped side (AC INPUT)
  11. Scaling knob for 9
  12. Cycle trigger (sends a pulse at the end of a cycle set by the Stepped rate) (Pulse OUTPUT)
  13. Knob for Stepped rate amount (sums with 9 x 11)
  14. CV output for thee Stepped module (DC OUTPUT)
  15. “Hot” Coupler output - +5V if Stepped output is higher than the Smooth output; -5V if not (AC Pulse OUTPUT)
  16. Regular Coupler output - +5V if Stepped output is higher than the Smooth output; 0V if not (Pulse OUTPUT)
  17. White noise source (AC OUTPUT)
  18. Pink noise source (AC OUTPUT)
  19. Sample-and-hold “dirty saw” source (DC OUTPUT)

Notes:

Dual Slopes #1

The Dual Slopes are the Random*Source implementation of a 1976 Serge module called the Dual Transient Generator (some Serge licensees still use that name; STS sells a related module called the Voltage-Controlled Timegen Oscillator). The module consists of the circuit for a Dual Universal Slope Generator (DUSG - see below) with a simplified panel interface, optimized for generating harmonically linked oscillators and clock pulses. The module contains two sides:

Dual Slopes

  1. Ramp output for the left-hand slope generator (DC OUTPUT)
  2. Ramp output for the right-hand slope generator (DC OUTPUT)
  3. Pulse output for the left-hand slope generator (Pulse OUTPUT)
  4. Pulse output for the right-hand slope generator (Pulse OUTPUT)
  5. Trigger “link switch”, internally patching a pulse generated at the end of the left envelope to trigger the right envelope
  6. External trigger input for the right-hand slope generator (Pulse INPUT)
  7. Signal input to the left-hand slope generator, causing it to act as a low-pass filter / envelope follower (AC INPUT)
  8. Signal input to the right-hand slope generator, causing it to act as a low-pass filter / envelope follower (AC INPUT)
  9. 1V-per-octave CV input to control the self-clocking frequency of the left-hand slope generator (sums with 11) (DC INPUT)
  10. Control knob for the Rise time on the right-hand slope - a higher value is a faster rise
  11. Control knob for the self-clocking frequency of the left-hand slope (sums with 9)
  12. Control knob for the Fall time on the right-hand slope - a higher value is a faster fall
  13. CV input to control the Fall time on the left-hand slope (scaled by 15) (DC INPUT)
  14. CV input to control either the Rise or Fall time on the right-hand slope (scaled by 16) (DC INPUT)
  15. Scaling knob for 13.
  16. Scaling knob for 16.
  17. Switch to set whether 14 x 16 controls the Rise or the Fall on the right-hand slope.

Notes:

Variable Slope Voltage Controlled Filter

Tcherepnin avoided implementing standard audio filters like those found on Moog and ARP synthesizers until 1976, preferring instead to focus on slew limiters, comparators, waveshapers, and other circuits that felt to him more natural as a designer. The Variable Slope Voltage Controlled Filter (VCFS) is a 12dB/octave state-variable filter that allows for voltage control over the slope of the filter, as well as its frequency.

Variable Slope VCF

  1. Bandpass filter output (AC OUTPUT)
  2. High-pass filter output (AC OUTPUT)
  3. Low-pass filter output (AC OUTPUT)
  4. Filter input 1 (AC INPUT)
  5. Filter input 2 (AC INPUT)
  6. Mix knob to control the blend between inputs 1 and 2
  7. Q knob for the “quality” (resonance) of the filter. This interacts with the slope to generate the specific behavior of the filter.
  8. 1-volt-per-octave CV input to control the filter frequency (sums with 10 x 12 and 14) (DC INPUT)
  9. Voltage control input for the filter’s slope (scaled by 11 and summed with 13) (DC INPUT)
  10. VC input for linear control of the filter frequency (scaled by 12 and sums with 8 and 14)
  11. Scaling knob for 9.
  12. Scaling knob for 10.
  13. Knob to set the base slope of the filter
  14. Knob to set the base frequency of the filter

Notes:

Variable Q Voltage Controlled Filter #1

The Variable Q Voltage Controlled Filter (VCFQ), sometimes referred to as the Variable Resonance Filter, is a 12dB/octave 2-pole state-variable filter that features low-pass, high-bass, band-pass, and band-reject outputs, voltage control over frequency and Q (resonance) of the filter, and multiple inputs, include one with automatic gain control and a pulse input that generates an impulse into the filter. The VCFQ is an extended range design, with a switch that allows it to filter sub-audio control voltage signals.

Variable Q VCF

  1. Bandpass filter output (AC OUTPUT)
  2. High-pass filter output (AC OUTPUT)
  3. Notch (band-reject) filter output (AC OUTPUT)
  4. Low-pass filter output (AC OUTPUT)
  5. Filter input (AC INPUT)
  6. Filter input with automatic gain control (AC INPUT)
  7. Pulse input to “ring” the filter - output will be the impulse response (Pulse INPUT)
  8. High/Low switch to choose the range of the filter between audio (“HIGH”) and sub-audio (“LOW”) frequencies
  9. 1-volt-per-octave CV input to control the filter frequency (sums with 11 x 13 and 15) (DC INPUT)
  10. Voltage control input for the filter’s Q (summed with 12) (DC INPUT)
  11. VC input for linear control of the filter frequency (scaled by 13 and sums with 9 and 15)
  12. Knob to set the base Q of the filter
  13. Scaling knob for 11
  14. Gain control knob for the filter
  15. Knob to set the base frequency of the filter

Notes:

Stereo Mixer

The Stereo Mixer is Random*Source’s take on Tcherepnin’s Dual Channel Stereo Mixer (DCSM) developed in the early 1980s. First and foremost, the module has 1/4” TRS jacks to output to non-Serge audio equipment. The module allows for voltage-controlled panning of its two inputs into a stereo output; it also allows for voltage control of the two input channel gains, allowing it to be used as a Dual VCA.

Stereo Mixer

  1. 1/4” TRS output of the left channel
  2. 1/4” TRS output of the right channel
  3. Left channel output (AC OUTPUT)
  4. Right channel output (AC OUTPUT)
  5. Auxiliary input for the left channel - bypasses panning and gain (AC INPUT)
  6. Auxiliary input for the right channel - bypasses panning and gain (AC INPUT)
  7. Channel 1 input (AC INPUT)
  8. Channel 2 input (AC INPUT)
  9. Panning voltage control for channel 1 (summed with 11) (AC INPUT)
  10. Panning voltage control for channel 2 (summed with 12) (AC INPUT)
  11. Panning knob for channel 1
  12. Panning knob for channel 2
  13. CV gain input for channel 1 (summed with 15) (DC INPUT)
  14. CV gain input for channel 2 (summed with 16) (DC INPUT)
  15. Gain control knob for channel 1
  16. Gain control knob for channel 2

Notes:

Panel 2 (Edelweiss II)

Random\*Source Edelweiss II

Dual Universal Slope Generator #1

The Dual Universal Slope Generator (DUSG), like the SSG, is one of the more complex Serge modules, developed in 1976 by combining the first generation Envelope Generator module with the Positive and Negative Slew modules. The DUSG can be used as an envelope generator, a low-pass filter / envelope follower, an oscillator, a harmonic subdivider, and a pulse delay. The module has two halves that are almost, but not quite, identical. DUSG #1 on the Random*Source Serge is a “contemporary” model, with a pulse output on the top half.

DUSG

  1. CV Slope Output (DC OUTPUT)
  2. Secondary slope output - a square wave output on the top half; an inverted bipolar output on the bottom half (Pulse OUTPUT / AC OUTPUT)
  3. Gate output (Pulse OUTPUT)
  4. Signal input for envelope follower (AC INPUT)
  5. 1 volt-per-octave input for slope generator (DC INPUT)
  6. CV input for envelope rise (scaled by 8 and summed with 10) (DC INPUT)
  7. CV input for envelope fall (scaled by 9 and summed with 11) (DC INPUT)
  8. Scaling knob for 6
  9. Scaling knob for 7
  10. Base knob for rise time (summed with 6 x 8)
  11. Base knob for fall time (summed with 7 x 9)
  12. Envelope trigger input (Pulse INPUT)

Notes:

Control Voltage Processor

The Control Voltage Processor, originally called the Dual Processor, is one of Tcherepnin’s original 1973 modules, and functions as a mixer / scalar for control voltages. The module is split into two halves, with up to three sources in each half that can be scaled independently, with an overall scalar for each half.

CV Processor

  1. Overall scaling knob or the output voltage
  2. Output of the control voltage processor (DC OUTPUT)
  3. First CV input (DC INPUT)
  4. Scalar knob for 3
  5. Second CV input (DC INPUT)
  6. Scalar knob for 5
  7. Third CV input (DC INPUT)
  8. Scalar knob for 7

Notes:

Dual Universal Slope Generator #2

The Dual Universal Slope Generator (DUSG), like the SSG, is one of the more complex Serge modules, developed in 1976 by combining the first generation Envelope Generator module with the Positive and Negative Slew modules. The DUSG can be used as an envelope generator, a low-pass filter / envelope follower, an oscillator, a harmonic subdivider, and a pulse delay. The module has two identical halves. DUSG #2 on the Random*Source Serge is a “classic” model, with an inverted bipolar output in addition to the slope output.

DUSG

  1. CV Slope Output (DC OUTPUT)
  2. Secondary inverted bipolar output (AC OUTPUT)
  3. Gate output (Pulse OUTPUT)
  4. Signal input for envelope follower (AC INPUT)
  5. 1 volt-per-octave input for slope generator (DC INPUT)
  6. CV input for envelope rise (scaled by 8 and summed with 10) (DC INPUT)
  7. CV input for envelope fall (scaled by 9 and summed with 11) (DC INPUT)
  8. Scaling knob for 6
  9. Scaling knob for 7
  10. Base knob for rise time (summed with 6 x 8)
  11. Base knob for fall time (summed with 7 x 9)
  12. Envelope trigger input (Pulse INPUT)

Notes:

Pulse Divider

The Pulse Divider is based on a design by Ken Stone, who developed a series of Serge-compatible modules in the 1980s and 1990s under the moniker the “Cat Girl Synth”, or CGS. PCBs for CGS modules are still sold by Elby Designs in Australia. The Pulse Divider takes a pulse input and outputs triggers on numerical subdivisions, allowing the user to have, e.g. a clock signal input generate a polyrhythmic output.

Divider

  1. Pulse input for divider (Pulse INPUT)
  2. Outputs a pulse every 2nd pulse (Pulse OUTPUT)
  3. Outputs a pulse every 3rd pulse (Pulse OUTPUT)
  4. Outputs a pulse every 4th pulse (Pulse OUTPUT)
  5. Outputs a pulse every 5th pulse (Pulse OUTPUT)
  6. Outputs a pulse every 6th pulse (Pulse OUTPUT)
  7. Outputs a pulse every 7th pulse (Pulse OUTPUT)
  8. Outputs a pulse every 8th pulse (Pulse OUTPUT)

Notes:

Boolean Logic

The Boolean Logic module is another design by Ken Stone, intended to expand on the comparator modules in the original Serge systems. It consists of two basic inverters at the top and bottom, and three submodules that set output voltages HIGH or LOW based on control voltage inputs:

Boolean Logic

  1. Input for top inverter (Pulse INPUT)
  2. Output for the top inverter - a HIGH input at 1 will cause a LOW output, and vice versa (Pulse OUTPUT)
  3. Input 1 for the AND comparator (DC INPUT)
  4. Input 2 for the AND comparator (DC INPUT)
  5. Output for the AND comparator (Pulse OUTPUT)
  6. Input 1 for the OR comparator (DC INPUT)
  7. Input 2 for the OR comparator (DC INPUT)
  8. Output for the OR comparator (Pulse OUTPUT)
  9. Input 1 for the XOR comparator (DC INPUT)
  10. Input 2 for the XOR comparator (DC INPUT)
  11. Output for the XOR comparator (Pulse OUTPUT)
  12. Input for bottom inverter (Pulse INPUT)
  13. Output for the bottom inverter - a HIGH input at 12 will cause a LOW output, and vice versa (Pulse OUTPUT)

Notes:

Divide-by-N Comparator

The Divide-by-N Comparator (÷N COM) is a circuit designed by Tcherepnin in 1979. The circuit is in two sections which have linked functionality. The bottom half of the module is a signal comparator, with a pulse output when one voltage rises above another. Thee top half counts the pulses from the bottom half, emitting its own pulses every N steps (hence the name) in increments up to 31. An additional output generates a “staircase” DC wave that rises with the number of steps coming from the comparator.

÷N Com

  1. “Divide-by-N” output pulse divider output (Pulse OUTPUT)
  2. Staircase output (DC OUTPUT)
  3. Knob for setting number of steps in the pulse divider (1-31)
  4. CV input for setting number of steps in the pulse divider (sums with 3)
  5. Comparator output (Pulse OUTPUT)
  6. Offset knob for comparator threshold (sums with 8)
  7. Positive (+) comparator input; if this signal is greater than (6 + 8), pulse output 5 will fire and the pulse divider will increment
  8. Negative (-) comparator input (sums with 6); if this signal is less than 7, pulse output 5 will fire and the pulse divider will increment

Notes:

Smooth / Stepped Generator #2

The Smooth / Stepped Generator (SSG) was designed by Tcherepnin in 1974. Along with the Dual Universal Slope Generator, it’s one of the most versatile circuits in the canonical Serge system. Depending on how an SSG is patched, it can function as a slew limiter (envelope follower / lowpass filter), a sample-and-hold circuit, a triangle wave oscillator, or a low-pass gate. SSG #2 on the Random*Source Serge system has no sidecar noise circuit, but can receive voltage from elsewhere in the system to create different random effects.

The module is divided into two halves: the “Smooth” side at the top, and the “Stepped” at the bottom. In between the two, a Coupler circuit outputs a comparator voltage of the two sides.

Smooth / Stepped Generator

  1. CV input for the Smooth sides’s rate (DC INPUT)
  2. CV output for the Smooth side (DC OUTPUT)
  3. Scaling knob for 1
  4. Cycle trigger (sends a pulse at the end of a cycle set by the Smooth rate) (Pulse OUTPUT)
  5. Knob for Smooth rate amount (sums with 1 x 3)
  6. Signal input for the Smooth side (AC INPUT)
  7. Hold jack - when set high, Smooth output 2 will freeze and no longer track the module’s input (Pulse INPUT)
  8. Sample jack - when set high, Stepped output 14 will sample and hold Stepped input 10 (Pulse INPUT)
  9. CV input for the Stepped side’s rate (DC INPUT)
  10. Signal input for the Stepped side (AC INPUT)
  11. Scaling knob for 9
  12. Cycle trigger (sends a pulse at the end of a cycle set by the Stepped rate) (Pulse OUTPUT)
  13. Knob for Stepped rate amount (sums with 9 x 11)
  14. CV output for thee Stepped module (DC OUTPUT)
  15. “Hot” Coupler output - +5V if Stepped output is higher than the Smooth output; -5V if not (AC Pulse OUTPUT)
  16. Regular Coupler output - +5V if Stepped output is higher than the Smooth output; 0V if not (Pulse OUTPUT)

Notes:

Random Source

The Random Source is the eponymous design of the company that designed its PCB in Berlin; it combines two of Tcherepnin’s noise modules: the Random Voltage Generator (RVG) (left column of the module) and the Noise Source (right column). The RVG behaves as a pre-patched Smooth / Stepped Generator fed with noise; the Noise Source provides a variety of noise sources to work with as well as a built-in sample-and-hold circuit.

Random Source

  1. Pulse output - generates random pulses at the module rate (specified by 9 x 10 + 12) (Pulse OUTPUT)
  2. Full-spectrum white noise (AC OUTPUT)
  3. Stepped random output - generates discrete random voltages at the module rate (DC OUTPUT)
  4. Pink Noise (AC OUTPUT)
  5. Smooth random output - generates continuous, low-pass filtered random voltages at the module rate (DC OUTPUT)
  6. “Dirty saw” - a circuit designed by Tcherepnin containing a sawtooth wave that wobbles in frequency and has low-amplitude noise injected in its signal (DC OUTPUT)
  7. Unipolar sample-and-hold output using 6 as its source and trigger 11 or 13 to sample the voltage (DC OUTPUT)
  8. Bipolar sample-and-hold output using 6 as its source and trigger 11 or 13 to sample the voltage (AC OUTPUT)
  9. CV input to set the rate of random outputs 1, 3, and 5 (scaled by 10 and sums with 12) (DC INPUT)
  10. Scalar knob for 9.
  11. Pulse input for the sample-and-hold outputs 7 and 8 (Pulse INPUT)
  12. Base rate for random outputs 1, 3, and 5 (sums with 9 x 10)
  13. Button to trigger the sample-and-hold outputs 7 and 8.

Notes:

Panel 3 (Mantra)

Random\*Source Mantra

Sequencer / Programmer

The Sequencer / Programmer module is Random*Source’s interpretation of a variety of Serge modules developed over the years. Serge 4-, 5-, 7-, and 8-stage Sequencing Programmer modules allowed for multiple stages of preset voltages that could be recalled either manually or in sequence from a pulse input. These stages were often arranged in rows, so that “preset 1” could recall up to four different voltages for different uses. This module is an eight stage, two row configuration.

Sequencer / Programmer

  1. CV output for the “A” row of presets (DC OUTPUT)
  2. CV output for the “B” row of presets (DC OUTPUT)
  3. CV output for the difference between the “A” and “B” voltages (DC OUTPUT)
  4. Gate output corresponding to manual button presses (Pulse OUTPUT)
  5. Reset - sets sequencer to first stage (Pulse INPUT)
  6. Up/Down - reverses direction of sequencer when HIGH (Pulse INPUT)
  7. Hold - temporarily disables sequencer when HIGH (Pulse INPUT)
  8. Clock - advances sequence one stage (Pulse INPUT)
  9. Sequencer on/off switch; off position only allows manual presets
  10. Buttons for manual presets
  11. “A” row of CV knobs for each preset stage
  12. “B” row of CV knobs for each preset stage

Notes:

Dual Universal Slope Generator XL

The Dual Universal Slope Generator XL (DUSG-XL) is an expanded version of the Dual Universal Slope Generator. Like the SSG, it is one of the more complex Serge modules, developed in 1976 by combining the first generation Envelope Generator module with the Positive and Negative Slew modules. The DUSG can be used as an envelope generator, a low-pass filter / envelope follower, an oscillator, a harmonic subdivider, and a pulse delay. The module has two (nearly) identical halves, along with a sidecar circuit that performs a peak / trough function on the generated slopes against a secondary signal.

DUSG XL

  1. Signal input for envelope follower (AC INPUT)
  2. 1 volt-per-octave input for slope generator (DC INPUT)
  3. CV input for envelope rise (scaled by 6 and summed with 5 and 8) (DC INPUT)
  4. CV input for envelope fall (scaled by 7 and summed with 5 and 9) (DC INPUT)
  5. CV input for both rise and fall (summed with 3 x 6 + 8 and 4 x 7 + 9) (DC INPUT)
  6. Scaling knob for 3
  7. Scaling knob for 4
  8. Base knob for rise time (summed with 3 x 6 and 5)
  9. Base knob for fall time (summed with 4 x 7 and 5)
  10. CV Slope Output (DC OUTPUT)
  11. Unipolar sinusoid output (DC OUTPUT)
  12. Inverted bipolar output (AC OUTPUT)
  13. Gate output that goes HIGH at the start of fall stage (Pulse OUTPUT)
  14. Square wave (pulse) output (Pulse OUTPUT)
  15. Gate / end output (Pulse OUTPUT)
  16. Envelope trigger input (Pulse INPUT)
  17. Peak comparator 2nd input (DC INPUT)
  18. Peak voltage output - the higher of 10 (top half) and 17 (DC OUTPUT)
  19. Trough voltage output - the lower of 10 (bottom half) and 20 (DC OUTPUT)
  20. Trough comparator 2nd input (DC INPUT)

Notes:

Active Processor

The Active Processor (Active Pro) is based on Tcherepnin’s design of the same name from 1979. It consists of a linear, DC-coupled, 2-input crossfader that can mix control voltages and/or audio signals using equal gain (as opposed to equal power) circuitry. The bottom section contains a “flip-flop” circuit with two outs that alternates which output is set to HIGH based on pulses at the input.

Active Pro

  1. Crossfaded signal (DC OUTPUT)
  2. Signal input 1 (DC INPUT)
  3. Signal input 2 (DC INPUT)
  4. Crossfade position voltage (sums with 5) (DC INPUT)
  5. Crossfade position knob (sums with 4)
  6. Flip (odd) gate (Pulse OUTPUT)
  7. Flop (even) gate (Pulse OUTPUT)
  8. Flip-flop input (Pulse INPUT)

Notes:

Smooth / Stepped Generator #3

The Smooth / Stepped Generator (SSG) was designed by Tcherepnin in 1974. Along with the Dual Universal Slope Generator, it’s one of the most versatile circuits in the canonical Serge system. Depending on how an SSG is patched, it can function as a slew limiter (envelope follower / lowpass filter), a sample-and-hold circuit, a triangle wave oscillator, or a low-pass gate. When combined with its sidecar Noise Source - a small circuit of three jacks - the SSG can be used to develop a wide variety of fluctuating and quantized random voltages, similar to the Buchla 266 Source of Uncertainty.

The module is divided into two halves: the “Smooth” side at the top, and the “Stepped” at the bottom. In between the two, a Coupler circuit outputs a comparator voltage of the two sides. The sidecar Noise Source provides three different types of random sources to work with, either with the SSG or with other modules in the system.

SSG

  1. CV input for the Smooth sides’s rate (DC INPUT)
  2. CV output for the Smooth side (DC OUTPUT)
  3. Scaling knob for 1
  4. Cycle trigger (sends a pulse at the end of a cycle set by the Smooth rate) (Pulse OUTPUT)
  5. Knob for Smooth rate amount (sums with 1 x 3)
  6. Signal input for the Smooth side (AC INPUT)
  7. Hold jack - when set high, Smooth output 2 will freeze and no longer track the module’s input (Pulse INPUT)
  8. Sample jack - when set high, Stepped output 14 will sample and hold Stepped input 10 (Pulse INPUT)
  9. CV input for the Stepped side’s rate (DC INPUT)
  10. Signal input for the Stepped side (AC INPUT)
  11. Scaling knob for 9
  12. Cycle trigger (sends a pulse at the end of a cycle set by the Stepped rate) (Pulse OUTPUT)
  13. Knob for Stepped rate amount (sums with 9 x 11)
  14. CV output for thee Stepped module (DC OUTPUT)
  15. “Hot” Coupler output - +5V if Stepped output is higher than the Smooth output; -5V if not (AC Pulse OUTPUT)
  16. Regular Coupler output - 5V if Stepped output is higher than the Smooth output; 0V if not (Pulse OUTPUT)
  17. White noise source (AC OUTPUT)
  18. Pink noise source (AC OUTPUT)
  19. Sample-and-hold “dirty saw” source (DC OUTPUT)

Notes:

Dual Slopes #2

The Dual Slopes are the Random*Source implementation of a 1976 Serge module called the Dual Transient Generator (some Serge licensees still use that name; STS sells a related module called the Voltage-Controlled Timegen Oscillator). The module consists of the circuit for a Dual Universal Slope Generator (DUSG - see below) with a simplified panel interface, optimized for generating harmonically linked oscillators and clock pulses. The module contains two sides:

Dual Slopes

  1. Ramp output for the left-hand slope generator (DC OUTPUT)
  2. Ramp output for the right-hand slope generator (DC OUTPUT)
  3. Pulse output for the left-hand slope generator (Pulse OUTPUT)
  4. Pulse output for the right-hand slope generator (Pulse OUTPUT)
  5. Trigger “link switch”, internally patching a pulse generated at the end of the left envelope to trigger the right envelope
  6. External trigger input for the right-hand slope generator (Pulse INPUT)
  7. Signal input to the left-hand slope generator, causing it to act as a low-pass filter / envelope follower (AC INPUT)
  8. Signal input to the right-hand slope generator, causing it to act as a low-pass filter / envelope follower (AC INPUT)
  9. 1V-per-octave CV input to control the self-clocking frequency of the left-hand slope generator (sums with 11) (DC INPUT)
  10. Control knob for the Rise time on the right-hand slope - a higher value is a faster rise
  11. Control knob for the self-clocking frequency of the left-hand slope (sums with 9)
  12. Control knob for the Fall time on the right-hand slope - a higher value is a faster fall
  13. CV input to control the Fall time on the left-hand slope (scaled by 15) (DC INPUT)
  14. CV input to control either the Rise or Fall time on the right-hand slope (scaled by 16) (DC INPUT)
  15. Scaling knob for 13.
  16. Scaling knob for 16.
  17. Switch to set whether 14 x 16 controls the Rise or the Fall on the right-hand slope.

Notes:

Variable Q Voltage Controlled Filter #2

The Variable Q Voltage Controlled Filter (VCFQ), sometimes referred to as the Variable Resonance Filter, is a 12dB/octave 2-pole state-variable filter that features low-pass, high-bass, band-pass, and band-reject outputs, voltage control over frequency and Q (resonance) of the filter, and multiple inputs, include one with automatic gain control and a pulse input that generates an impulse into the filter. The VCFQ is an extended range design, with a switch that allows it to filter sub-audio control voltage signals.

Variable Q VCF

  1. Bandpass filter output (AC OUTPUT)
  2. High-pass filter output (AC OUTPUT)
  3. Notch (band-reject) filter output (AC OUTPUT)
  4. Low-pass filter output (AC OUTPUT)
  5. Filter input (AC INPUT)
  6. Filter input with automatic gain control (AC INPUT)
  7. Pulse input to “ring” the filter - output will be the impulse response (Pulse INPUT)
  8. High/Low switch to choose the range of the filter between audio (“HIGH”) and sub-audio (“LOW”) frequencies
  9. 1-volt-per-octave CV input to control the filter frequency (sums with 11 x 13 and 15) (DC INPUT)
  10. Voltage control input for the filter’s Q (summed with 12) (DC INPUT)
  11. VC input for linear control of the filter frequency (scaled by 13 and sums with 9 and 15)
  12. Knob to set the base Q of the filter
  13. Scaling knob for 11
  14. Gain control knob for the filter
  15. Knob to set the base frequency of the filter

Notes:

Equal Power XFader

The Random*Source Equal Power XFader (XFader) is a design based on Tcherepnin’s Cross-Fader module for the Serge. It crossfades two audio (AC) signals, with an additional control for overall gain and a 1/4” TRS output to connect to external audio equipment.

XFader

  1. 1/4” TRS output for the crossfader
  2. Crossfaded signal (AC OUTPUT)
  3. Signal input 1 (AC INPUT)
  4. Signal input 2 (AC INPUT)
  5. Crossfade (“Xfade”) position voltage (sums with 6) (DC INPUT)
  6. Crossfade position knob (sums with 5)
  7. Voltage control input for overall gain (sums with 8) (DC INPUT)
  8. Overall gain knob (sums with 7).

Notes:

Panel 4 (TKB)

Random\*Source Touch Activated Keyboard Sequencer

Touch Activated Keyboard Sequencer

The Serge Touch Activated Keyboard Sequencer (TKB) had its debut in 1976, and is considered one of the most historically influential of Tcherepnin’s designs. A combination 16-stage preset manager with 4 rows, sequencer, and keyboard controller, this single module takes up an entire panel in our Serge system. It was the most expensive item in the Serge Modular Music Systems catalog, selling in 1982 for $900 pre-assembled ($2,400 in 2019 dollars).

Tcherepnin, like Don Buchla, rejected implementing Western-style keyboard controllers with white keys and black keys, arranged according to the chromatic scale. Instead, Tcherepnin used capacitive touch pads arranged in an evenly spaced pattern, similar to the touch strips on the Buchla model 112. The touch pads on the TKB output the voltage presets set by four rows of knobs (A, B, C, and D) above the pads, as well as a voltage based on the “pressure” applied to the key.

Unlike the Buchla touch controllers, the Serge TKB doubles as a sophisticated sequencer, with pulse output triggers above each stage, the ability to reverse direction, and so forth. It also includes a vertical clock to generate one long (64-value) set of voltages from the four independent rows, a random selector input, and many other features.

TKB

  1. “ABCD” 64-stage output, driven by the clock and vertical clock (15 and 16) (DC OUTPUT)
  2. CV output for the “A” row of presets (DC OUTPUT)
  3. CV output for the “B” row of presets (DC OUTPUT)
  4. CV output for the “C” row of presets (DC OUTPUT)
  5. CV output for the “D” row of presets (DC OUTPUT)
  6. “Key Vert” CV out - voltage corresponds to the specific key pad pressed in 1/6V increments (similar to the staircase output on the ÷N COM) (DC OUTPUT)
  7. Pulse output when a key is pressed (Pulse OUTPUT)
  8. CV output for key “pressure” - in reality, this corresponds more to the surface area of the pad covered by finger contact than actual pressure (DC OUTPUT)
  9. Reset input - sets the sequencer stage back to 1 (Pulse INPUT)
  10. Vertical reset input - sets the vertical clock back to “A” (Pulse INPUT)
  11. Random input - causes the sequencer to jumb to a random position (Pulse INPUT)
  12. Keyboard on/off switch - when set to “off”, the TKB will only respond to external triggers and not the keyboard
  13. Up/Down input - when set HIGH, the sequencer will reverse direction (Pulse INPUT)
  14. Hold input - when set HIGH, the sequencer will pause and ignore clock pulses (Pulse INPUT)
  15. Clock input - pulses will advance the (horizontal) sequencer (Pulse INPUT)
  16. Vertical clock input to advance the row of presets used for the “ABCD” output 1 (Pulse INPUT)
  17. Glide switch - when on, the knobs on row “B” set a portamento (glide) value for the presets on row “A”
  18. Pulse outputs for each stage of the sequencer (Pulse OUTPUT)
  19. “A” row of CV knobs for each preset stage
  20. “B” row of CV knobs for each preset stage
  21. “C” row of CV knobs for each preset stage
  22. “D” row of CV knobs for each preset stage
  23. Capacitive touch pads (the “keys”) for the TKB

Notes:

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Panel 5 (Custom)

Random\*Source Serge Panel V

Tau “The Pipe” Phaser

The Tau Phaser was invented by reknowned electronic music instrument designer Jürgen Haible (1964-2011). It consists of a 20-pole, stereo Phaser that leverages voltage control to allow other modules in the Serge system to dynamically modulate its parameters. The Phaser was designed to mimic the effects of classic Analog phasers from the 1970s such as the phase shifter on the ARP Quadra, with the addition of a feedback stage that allowed for flanging effects that go beyond the “Leslie speaker”-style sound of most phaser circuits. Originally designed to be used as an effect pedal, the Tau Phaser was refactored by Random*Source to fit in a Serge 4U module.

Tau Phaser

  1. Signal input (AC INPUT)
  2. 1 volt-per-octave input for phaser “pitch” (sums with 6 and 14) (AC INPUT)
  3. CV input for LFO rate (scaled by 7, sums with 12) (AC INPUT)
  4. Audio output 1 (180 degrees out-of-phase with 8) (AC OUTPUT)
  5. Input scaling knob
  6. inverted 1 volt-per-octave input for phaser “pitch” (sums with 2 and 14) (AC INPUT)
  7. CV scaling knob
  8. Audio output 2 (180 degrees out-of-phase with 4) (AC OUTPUT)
  9. Hard/Smooth switch to change LFO waveform from saw (“hard”) to sine (“smooth”)
  10. Vibrato/Phaser switch - in “Vibrato” mode, the filters are bypassed for an amplitude modulation effect
  11. Color/Normal switch - in “Color” mode, the feedback stage is engaged to create flanging effects
  12. LFO Rate knob (sums with 3x7)
  13. LFO Level (depth) knob
  14. Pitch knob for feedback stage (sums with 2 and 6)
  15. Feedback amount knob
  16. LEDs showing amplitude of outputs 4 and 8

Notes:

Triple + Waveshaper / New Ring (TWS+)

The Triple + Waveshaper / New Ring (TWS+) is a module with updated versions of Tcherepnin’s original Triple Waveshaper and Ring Modulator (both of which are on the 73-75 Serge). The Triple + Waveshaper consists of three waveshapers that distort an input signal, with voltage control of the shaping curve and “gang” switches that allow them to be used in series. A fourth, fixed waveshaping circuit can be dialed in to further transform the signal. The New Ring allows for both amplitude and ring modulation effects by multiplying an audio input signal with an AC or DC “carrier” signal.

TWS+

  1. Waveshaper 1-3 outputs (AC or DC OUTPUT depending on input)
  2. Strength knob of 4th (“+”) waveshaper in series after Waveshaper 1
  3. Link switch putting Waveshaper 2 in series after Waveshaper 1
  4. Link switch putting Waveshaper 3 in series after Waveshaper 2
  5. Input signal for Waveshaper 1-3 (AC INPUT)
  6. Gain knob for Waveshaper 1-3
  7. CV 1 input for Waveshaper 1-3
  8. Scalar knob for CV 1
  9. CV 2 input for Waveshaper 1-3
  10. Scalar knob for CV 2
  11. Ring modulator output (AC OUTPUT)
  12. Audio input for ring modular (AC INPUT)
  13. Bipolar “carrier” input for ring modulator (AC INPUT)
  14. Gain knob for 13
  15. Unipolar “carrier” input for ring modular (DC INPUT)
  16. Scaling knob for 15
  17. Crossfader knob between DC and AC carrier inputs

Notes:

Wave Multipliers / Resonant Equalizer

The Wave Multipliers module appeared in 1976 and is considered an important circuit for achieving the “West Coast” sound of the Serge modular. The module contains three self-contained distortion effects that work by shaping the amplitude of the incoming audio signal. Quoting from the 1982 Serge catalog, Tcherepnin describes the three Wave Multipliers:

The uppermost section is the simplest of the three multiplier sections. but it has two switchable effects. With the switch set at the “HI” position, the module functions to “square-up” an incoming signal. This is not the same as a simple comparator squaring function, though, since there is a rounded flattening of the signal peaks: an effect somewhat similar to overdriving a tube amplifier (except that in this version the process is voltage controllable!). With the switch in the “LO” position, the module is a linear gain controlled VCA. This is useful for various functions such as amplitude modulation and for gating signals into the other sections.

The middle Wave Multiplier provides a sweep of the odd harmonics (1, 3, 5, 7, 9, 11 and 13th) when a sine wave is applied to its input and the knob is turned up or a control voltage is swept from low to high. This effect is similar to overblowing a wind pipe closed at one end, and thus the module can be used to produce the sounds of various wind instruments. A second input is included to allow two signals to be mixed before processing, a technique that we have found to be very usable. This module can be used to explore timbral areas beyond the range of ring modulation because there are more varied harmonics than the sum and difference tones.

The bottom Wave Multiplier performs non-linear wavehaping known as full-wave rectification, but with sophisticated level- compensating conditioning as well. Actually the circuit uses three full-wave rectifier sections linked in a very refined controllable format. Each section can double the frequency of a sine or triangle wave applied to its input. Thus sweeping the VC input over its range will produce a smooth timbral transition using the even harmonics (second, fourth, and eighth). Many other partials are present in this basic sound, however, and the sonorities are very rich and varied. A notable feature of this multiplier is that the full-wave rectification is not accompanied by a reduction in the output amplitude. There is no alteration of the essential level of the sound. There are two inputs to provide mixing before processing, and two outputs. One output is a “squared up” version of the other. This output resembles voltage controlled pulse width modulation (only much more interesting).

The Serge Resonant Equalizer was designed by Tcherepnin in 1979, and consists of a bank of ten parallel bandpass filters, deliberately tuned at a non-integer harmonic interval of a major seventh. The individual filters can boost or cut, and a feedback circuit allows them to resonate as a comb filter, similar to the Buchla 296.

Wave Multipliers / Resonant EQ

  1. CV input for Multiplier 1 amount (DC INPUT)
  2. Processed output of Multiplier 1 (AC OUTPUT)
  3. Scaling knob for Multiplier 1 amount
  4. Signal input for Multiplier 1 (AC INPUT)
  5. High/Low distortion switch for Multiplier 1
  6. Processed output of Multiplier 2 (AC OUTPUT)
  7. CV input for Multiplier 2 amount (DC INPUT)
  8. Second signal input for Multiplier 2 (DC INPUT)
  9. Scaling knob for Multiplier 2 amount
  10. First signal input for Multiplier 2 (AC INPUT)
  11. Second processed (“squared-up”) output for Multiplier 3 (DC OUTPUT)
  12. First processed output for Multiplier 3 (AC OUTPUT)
  13. CV input for Multiplier 2 amount (DC INPUT)
  14. Second signal input for Multiplier 3 (AC INPUT)
  15. Scaling knob for Multiplier 3 amount
  16. First signal input for Multiplier 3 (AC INPUT)
  17. Output of Resonant EQ (AC OUTPUT)
  18. Positive “Comb” output of Resonant EQ (AC OUTPUT)
  19. Negative “Comb” output of Resonant EQ (AC OUTPUT)
  20. Boost-cut knobs for the ten bandpass filters (29Hz, 61Hz, 115Hz, 218Hz, 411Hz, 777Hz, 1.5kHz, 2.8kHz, 5.2kHz, 11kHz)
  21. Phase switch for the feedback stage
  22. Feedback amount knob
  23. Audio input for the Resonant EQ (AC INPUT)
  24. Gain knob for the Resonant EQ input

Notes:

Dual Lowpass Gate / Timbre / Stereo Mixer (DONKS)

The Dual Lowpass Gate / Timbre / Stereo Mixer (DONKS) is a combination of three amplitude processing modules. The Dual Lowpass Gate is modeled after the Buchla Quad Lopass Gate Model 292, developed as part of the “200 Series” in the 1970s; the Lowpass Gate uses Vactrol opto-isolators to create a combination VCF/VCA. The Timbre module is based on Buchla’s wavefolder circuit used in the Complex Wave Generator Model 259 as well as the oscillator in the Music Easel; similar to the Serge Wave Multipliers, the module performs harmonic distortion on an input signal to create a more complex waveform. The Stereo Mixer is Random*Source’s take on Tcherepnin’s Dual Channel Stereo Mixer (DCSM) developed in the early 1980s. First and foremost, the module has 1/4” TRS jacks to output to non-Serge audio equipment. The module allows for voltage-controlled panning of its two inputs into a stereo output; it also allows for voltage control of the two input channel gains, allowing it to be used as a Dual VCA.

DONKS

  1. Output for Lowpass Gate channel 1 (AC OUTPUT)
  2. Output for Lowpass Gate channel 2 (AC OUTPUT)
  3. Lowpass Gate mix output (AC OUTPUT)
  4. Crossfader knob for 3
  5. Lowpass Gate channel 1 input (AC INPUT)
  6. Lowpass Gate channel 2 input (AC INPUT)
  7. CV gain input for Lowpass Gate channel 1 input (DC INPUT)
  8. CV gain input for Lowpass Gate channel 2 input (DC INPUT)
  9. Gain control knob for Lowpass Gate channel 1 input (DC INPUT)
  10. Gain control knob for Lowpass Gate channel 1 input (DC INPUT)
  11. Mode switch for Lowpass Gate channel 1
  12. Mode switch for Lowpass Gate channel 2
  13. Signal output for Timbre module (AC OUTPUT)
  14. CV distortion input for Timbre module (scaled by 16) (DC INPUT)
  15. Signal input for Timbre module (AC INPUT)
  16. Distortion knob for Timbre module
  17. 1/4” TRS output of the Stereo Mixer left channel
  18. 1/4” TRS output of the Stereo Mixer right channel
  19. Stereo Mixer left channel output (AC OUTPUT)
  20. Stereo Mixer right channel output (AC OUTPUT)
  21. Auxiliary input for the Stereo Mixer left channel - bypasses panning and gain (AC INPUT)
  22. Auxiliary input for the Stereo Mixer right channel - bypasses panning and gain (AC INPUT)
  23. Stereo Mixer channel 1 input (AC INPUT)
  24. Stereo Mixer channel 2 input (AC INPUT)
  25. Panning voltage control for Stereo Mixer channel 1 (summed with 11) (AC INPUT)
  26. Panning voltage control for Stereo Mixer channel 2 (summed with 12) (AC INPUT)
  27. Panning knob for Stereo Mixer channel 1
  28. Panning knob for Stereo Mixer channel 2
  29. CV gain input for Stereo Mixer channel 1 (summed with 15) (DC INPUT)
  30. CV gain input for Stereo Mixer channel 2 (summed with 16) (DC INPUT)
  31. Gain control knob for Stereo Mixer channel 1
  32. Gain control knob for Stereo Mixer channel 2

Notes:

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73-75 Serge

73-75 Serge system

The 73-75 Serge was built by Luther Bradfute based on a kit designed by the Human Comparator in Stockholm as part of their 73-75 project, which aims to revisit the original Serge Modular DIY designs. Called the “Homebuilt” system, this 2-panel setup contains a “greatest hits” of Serge modules from the first generation of Tcherepnin’s synthesizers, built in his home and sold as kits while he was still working at CalArts from 1973-1975. In general, these modules are simpler than found on the Random*Source panels, but contain many examples of Tcherepnin’s innovative designs.

“Homebuilt” Panel 1

73-75 Panel 1

Oscillator

The 73-75 Oscillator has two sets of oscillator outputs - a variable waveform that goes from sine to sawtooth, and a pure sawtooth waveform (the circuit’s oscillator core). Both outputs can be tapped as AC or DC signals, and the oscillator can be synced.

Oscillator

  1. Bipolar variable waveform, controlled by 3 and 4 (AC OUTPUT)
  2. Unipolar variable waveform, controlled by 3 and 4 (DC OUTPUT)
  3. Control knob for variable waveform shape (sine to square - sums with 4)
  4. CV input for variable waveform shape (sums with 3) (DC INPUT)
  5. Unipolar sawtooth waveform (DC OUTPUT)
  6. Bipolar sawtooth waveform (AC OUTPUT)
  7. CV frequency 1 (scaled by 9, sums with 8 x 10 and 12) (DC INPUT)
  8. CV frequency 2 (scaled by 10, sums with 7 x 9 and 12) (DC INPUT)
  9. Scalar knob for 7
  10. Scalar knob for 8
  11. Oscillator sync input for sawtooth outputs 5 and 6 (AC INPUT)
  12. Knob for base oscillator frequency (sums with 7 x 9 and 8 x 10)

Notes:

Triple Waveshaper

The Serge Triple Waveshaper (TWS), along with the Wave Multipliers (found on the Random*Source system), are considered classic examples of modules that perform “West Coast” synthesizer distortion. Consisting of three sets of waveshapers with CV control, the modules are designed to be patch-programmed to interact with one another in different ways.

TWS

  1. Signal to be waveshaped (AC INPUT)
  2. Waveshaper CV 2 (DC INPUT)
  3. Waveshaper CV 1 (DC INPUT)
  4. Knob for waveshaper amount (summed with 2 and 3)
  5. Bipolar output (AC OUTPUT)
  6. Unipolar output (DC OUTPUT)

Notes:

Peak / Trough

The 73-75 Peak / Trough is quite simple, but exemplifies Tcherepnin’s instrument design aesthetic of “letting the circuit suggest the sound, rather than the sound suggest the circuit”. The module has two sides: the left side (the “Peak”) outputs the highest signal that appears at its inputs; the right side (the “Trough”) outputs the lowest.

Peak / Trough

  1. “Peak” (highest) signal of the left-side inputs (DC OUTPUT)
  2. “Trough” (lowest) signal of the right-side inputs (DC OUTPUT)
  3. Inputs for “Peak” circuit (DC INPUT)
  4. Inputs for “Trough” circuit (DC OUTPUT)

Notes:

Triple Comparator

The Triple Comparator is Tcherepnin’s first “Boolean” module, consisting of three identical circuits that send a pulse output HIGH whenever their “+” input rises above their “-“ input. A knob can set a fixed DC threshold instead of a varying “-“ input.

Triple Comparator

  1. Comparator result - HIGH if 2 > 3 + 4; LOW otherwise (Pulse OUTPUT)
  2. ”+” signal (DC INPUT)
  3. ”-“ signal (sums with 4) (DC INPUT)
  4. ”-“ threshold knob (sums with 3)

Notes:

Dual Processor

The Dual Processor is a first-generation Tcherepnin design that has survived, more-or-less unchanged, as a standard module in the Serge repertoire (on our Random*Source system, it’s called the Control Voltage Processor). It functions as a mixer / scalar for control voltages. The module is split into two halves, with up to three sources in each half that can be scaled independently, with an overall scalar for each half.

Dual Processor

  1. Output of the control voltage processor (DC OUTPUT)
  2. Overall scaling knob or the output voltage
  3. First CV input (DC INPUT)
  4. Scalar knob for 3
  5. Second CV input (DC INPUT)
  6. Scalar knob for 5
  7. Third CV input (DC INPUT)
  8. Scalar knob for 7

Notes:

Ring Modulator

The Serge Ring Modulator was one of Tcherepnin’s earliest designs, and allows for the multiplication of bipolar and unipolar signals to create a variety of effects. A control knob controls the strength of the effect.

Ring

  1. Output of Ring Modulator (AC OUTPUT)
  2. Bipolar Y (Modulator) source (AC INPUT)
  3. Unipolar Y (Modulator) source (DC INPUT)
  4. Bipolar X (Carrier) source (AC INPUT)
  5. Unipolar X (Carrier) source (DC INPUT)
  6. Effect control knob - fades from X input only to XY (fully modulated)

Notes:

Gate

The 1973 Serge Gate module was Tcherepnin’s first VCA design, allowing the amplitude of input signals to be modified by a second envelope signal. The module has inputs for both linear and logarithmic amplitude scaling as well as an overall gain control.

Gate

  1. VCA output (AC OUTPUT)
  2. Bipolar input (sums with 3) (AC INPUT)
  3. Unipolar input (sums with 2) (DC INPUT)
  4. Linear CV gain (DC INPUT)
  5. Logarithmic CV gain (DC INPUT)
  6. Scaling knob for overall gain (scales with 4 and 5)

Notes:

Reverb

The 1973 Serge Reverb unit uses a mounted spring reverberation tank on the back of the panel to add a reverb effect to the incoming signal.

Reverb

  1. Mixed reverb outputs (AC OUTPUT)
  2. Mix control knob
  3. Direct reverb outputs (AC OUTPUT)
  4. Reverb input (AC INPUT)

Notes:

Preamp

The Serge Preamp provides a gain stage to allow a high-impedance signal to be input into the Serge system.

Preamp

  1. 1/4” TRS input to the preamplifier
  2. Gain control knob
  3. Amplified outputs (AC OUTPUT)

Notes:

“Homebuilt” Panel 2

73-75 Panel 2

Dual Positive Slew

The Dual Positive Slew is the forerunner to the Dual Universal Slope Generator (DUSG - found on our Random*Source Serge), and is an early example of Tcherepnin’s desire to make modules that perform more than one function with the same circuit. It can perform slew limiting on a rising input signal to function as the first half of an envelope follower (the Dual Negative Slew providing the other half). It can also be patched to oscillate as a rising sawtooth LFO or generate a rising envelope. The module contains two identical circuits laid out in an upper and lower half.

Positive Slew

  1. VC input for slew limiter amount (scaled by 2, sums with 9) (DC INPUT)
  2. Scaling knob for 1
  3. Input signal (DC INPUT)
  4. Output signal (DC OUTPUT)
  5. “Start” envelope trigger (Pulse INPUT)
  6. “Sustain” envelope trigger (Pulse INPUT)
  7. Gate signal (Pulse OUTPUT)
  8. End signal (Pulse OUTPUT)
  9. Slew base amount (sums with 1 x 2)

Notes:

Dual Negative Slew

The Dual Negative Slew is the complement to the Dual Positive Slew, and like its counterpart was incorporated by Tcherepnin into the Dual Universal Slope Generator in 1976. It can perform slew limiting on a falling input signal to function as the second half of an envelope follower (the Dual Positive Slew providing the other half). It can also be patched to oscillate as a falling sawtooth LFO or generate a falling envelope. The module contains two identical circuits laid out in an upper and lower half.

Negative Slew

  1. VC input for slew limiter amount (scaled by 2, sums with 6) (DC INPUT)
  2. Scaling knob for 1
  3. Input signal (DC INPUT)
  4. Output signal (DC OUTPUT)
  5. “End” trigger (Pulse OUTPUT)
  6. Slew base amount (sums with 1 x 2)

Notes:

Envelope Generator #1, #2, #3

The 1973 Envelope Generator (EG) modules generate attack-release envelopes, with added features to make them usable as oscillators and sample-and-hold modules. The three EG modules in the 73-75 system are identical.

Envelope Generator

  1. “Start” trigger for the envelope generator (Pulse INPUT)
  2. “End” trigger for the envelope generator (Pulse OUTPUT)
  3. Envelope signal (DC OUTPUT)
  4. Gate signal (Pulse OUTPUT)
  5. Knob to set window size of gate (summed with 6)
  6. CV input to set window size of gate (summed with 5) (DC INPUT)
  7. “Cycle” trigger for the envelope generator (Pulse INPUT)
  8. “Hold” trigger for the envelope generator (Pulse INPUT)
  9. CV input for overall duration (sums with 10 and scales 11 and 12) (DC INPUT)
  10. Base duration for EG (sums with 9 and scales 11 and 12)
  11. Fall time for envelope (scaled by 9 + 10)
  12. Rise time for envelope (scaled by 9 + 10)

Notes:

Adapter

The Adapter is a passive utility module that converts between banana jacks and 3.5mm / 1/8” connectors. There are three pairs of connectors in the module, and each converter can be used as an input or an output to the Serge.

Adapter

  1. 1/8” connector
  2. Banana connector (any INPUT or OUTPUT)

Notes:

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Ian Fritz Panels

Ian Fritz Serge panels

The Ian Fritz Panels were developed by Paul Akin at Uglysound Electronics (USE) in 2014, and consist of Serge-compatible implementations of synthesis, signal processing, and control circuits designed by Ian Fritz. Fritz has been developing and publishing open-source analog synthesizer designs since 1998, and is considered, along with Jürgen Haible and Ken Stone, to be one of the most important contributors to the DIY analog synthesizer community. Fritz’s designs focus on pushing the technical and creative repertoire of what are considered core analog synthesis modules - oscillators, filters, waveshapers, envelope generators, amplifiers, and noise generators are all reconsidered by Fritz and featured in these panels. In many ways the opposite of the 73-75 Serge, Fritz’s modules contain more complex circuitry than found in Tcherepnin’s designs, but retain the Serge sensibility of patch programmability - each module has many potential uses and can be connected with the other modules in the studio in an infinite number of ways.

Note: The Fritz panels deviate from the Serge standard somewhat in terms of panel layout and user interface conventions. Paul Akin’s implementation of Fritz’s designs include a number of UI elements - sliders, ten-turn dials, stepped potentiometers - that don’t appear on original Serge equipment. More importantly, the Fritz modules are not always contained in vertical slices, and the layout of “outputs over inputs” on a module is not followed - in fact, it’s often reversed, with module outputs at the bottom of the panel in a layout similiar to many Eurorack systems. When working with the Fritz panels, you may need to double-check your connections to make sure your inputs and outputs are correct.

Panel 1 (The Timbre Tantrum)

Ian Fritz Panel 1

DoubleDeka Ultrasonic VCO

The DoubleDeka Ultrasonic VCO was Ian Fritz’s first published synthesizer circuit. Unlike most modern VCOs, this design uses an ultrasonic oscillator core - the primary oscillator is above the range of human hearing. A pair of frequency dividers allow you to lower the pitch into two (subharmonically related) frequencies, each of which is then synthesized by a ten-step waveform outlined by the slide potentiometers on the interface. These slider banks represent actual steps in the output wave, similar to a breakpoint function generator such as the Buchla MARF, and unlike organ drawbars, where the sliders would represent the strengths of different harmonics in the signal.

Early synthesizers (and some electric organs) used electronic or mechanical ultrasonic oscillators, and would generate an audible frequency either through frequency division or heterodyning, in a manner similar to a Theremin. Fritz’s technique is designed to be more stable and accurate over a wide range of frequencies than traditional VCO designs. In addition, the DoubleDeka contains an unusual oscillator sync circuit and a “digital” ring modulator that allow for the creation of a wide range of sounds.

DoubleDeka Ultrasonic VCO

  1. Waveform sliders for Bank A
  2. Waveform sliders for Bank B
  3. Coarse frequency knob (summed with 4 and 13)
  4. Fine frequency knob (summed with 3 and 13)
  5. Signal input for ring modulator (AC INPUT)
  6. Oscillator sync input (AC INPUT)
  7. Harmonic / aharmonic switch for oscillator sync
  8. Scaling knob for exponential FM input
  9. Exponential Frequency Modulation (FM) input (scaled by 8)
  10. Scaling knob for linear FM input
  11. AC/DC switch for linear FM input
  12. Linear Frequency Modulation (FM) input (scaled by 10) (AC INPUT)
  13. 1V-per-octave input (summed with 3 and 4) (DC INPUT)
  14. Bank A signal output (AC OUTPUT)
  15. Bank B signal output (AC OUTPUT)
  16. Bank A octave selection knob
  17. Bank B octave selection knob
  18. High frequency oscillator core output (AC OUTPUT)

Notes:

Teezer TZFM VCO

The Teezer Through-Zero FM VCO is Fritz’s design for a sawtooth-core oscillator that can do true, bipolar (or “through zero”) frequency modulation, using an entirely analog signal path. Typical analog FM circuits were designed to create sonic effects ranging from vibrato to noisy, warped timbres using a second oscillator as a modulating source. These signals typically summed into the existing DC voltage chain controlling the oscillator’s frequency, meaning that they only modulated the oscillator in a positive direction. To generate “true” FM synthesis, as developed by John Chowning and most famously implemented on digital synthesizers such as the Yamaha DX7, the frequency of the primary oscillator needs to be able to go negative as well.

The Teezer VCO, by allowing for bipolar FM, can be used to synthesize sounds with the full repertoire of FM effects, including rich sidebands that behave in a nonlinear fashion that can be used to create brassy tones, bell sounds, and other rich, time-varying spectra. The VCO has outputs for triangle, sine, and sawtooth waveforms, and ten-turn precision dials can be used to set the base frequency of both the primary oscillator and the FM circuitry.

Teezer TZFM VCO

  1. Coarse frequency knob (sums with 2 and 11)
  2. Fine frequency knob (sums with 1 and 11)
  3. Sync scaling knob
  4. Sync signal input (scaled by 3) (AC INPUT)
  5. Linear FM scaling knob
  6. Linear Frequency Modulation (FM) input (scaled by 5, sums with 8) (AC INPUT)
  7. AC/DC switch for linear FM input
  8. Initial FM frequency knob (sums with 5 x 6)
  9. Exponential Frequency Modulation (FM) input (scaled by 10) (DC INPUT)
  10. Exponential FM scaling knob
  11. 1V-per-octave input (sums with 1 and 2) (DC INPUT)
  12. Triangle waveform output (AC OUTPUT)
  13. Sine waveform output (AC OUTPUT)
  14. Sawtooth waveform output (AC OUTPUT)

Notes:

Wavolver II

The Wavolver II is one of Fritz’s unique waveshaping circuits, designed in the spirit of Tcherepnin’s Wave Multipiers and Triple Waveshaper, as well as the wavefolder circuit on the Buchla Music Easel. Akin’s description of the module explains:

The Wavolver is a novel, versatile waveshaper that generates a special kind of double-pulse waveform along with an extra folded-wave section added between the pulses. It generates a wide range of timbres from a gentle sine or triangle wave to a very rich signal with multiple zero-crossings per cycle.

The module can be driven by any continuously varying signal. For simplicity let’s assume a Tri wave at the input. The circuitry works by only passing the input signal when its amplitude (positive or negative) is above a threshold set by the Pulse Width control. When it’s below the threshold the output signal is zero. This is shown on the left side of the following figure. The signal consists of steeple-shaped pulses that can be swept from narrow for high harmonic content to full width, which results in a triangle wave (“Width” and “Width mod” controls). This represents a wider range of timbres than from the familiar rectangular pulse generators, which give a square waves at full width.

In addition to the double-pulse generator, the Wavolver has circuitry to generate a series of evolving folded waves between the pulses. These are mixed into the output via the “Fold mix” control. The right side of the above figure illustrates the folding at a 50% level for two different pulse widths. The folder output is available separately to allow individual processing of the double pulses and the folds.

The double-pulse signal consists of a positive pulse and a negative one, and the resulting signal has odd harmonics only. The capability to produce waves with strong, odd-only harmonics is practically never seen in classical VCO/waveshaper designs. There is a wide area of timber space available here that has been largely ignored. Adding the folder output produces high-energy even harmonics in the signal’s spectrum.

In the Wavolver II there are several ways to modify the basic waveforms discussed above. First, the amplitude of the second pulse can be continuously tuned from -5V (as shown above) to +5V (“Pulse 2 amp” control). At full positive amplitude, the signal has two identical positive pulses, resulting in a signal at twice the frequency of the driving signal. Waves with the second harmonic stronger than the fundamental are musically useful, as some acoustic instruments (bowed strings) share this characteristic.

Another way to change the basic waveforms is to add a DC voltage offset to the input signal (“Offset” and “Offset mod” controls). A positive offset makes the first pulse stronger and wider and at the same time it make the second pulse weaker and narrower. Again, this adds even harmonics into the output spectrum and results in some interesting timbres, especially when modulated. The graphic below illustrates these modifications.

Finally, the waveshape can be modulated by modulating the input waveform.

Wavolver II

  1. Pulse width knob (sums with 2 x 3)
  2. Pulse width modulation scaling knob
  3. Pulse width modulation (PWM) signal input (sums with 1, scaled by 3) (DC INPUT)
  4. Waveshaper signal input (AC INPUT)
  5. Waveshaper signal output (AC OUTPUT)
  6. Folded signal output (AC OUTPUT)
  7. Waveshaper strength knob (sums with 8 x 9)
  8. Waveshaper CV scaling knob
  9. Waveshaper strength input (sums with 7, scaled by 8) (DC INPUT)
  10. PWM 2nd order strength knob
  11. Folded signal mix knob

Notes:

Threeler VCF

The Threeler Voltage-Controlled Filter is a three-stage series of first-order state-variable filters where each stage can be tapped independently and chained together in either highpass or lowpass configurations. This allows you to combine the stages to create highly resonant lowpass, highpass, and bandpass topologies while also having access to outputs of the individual filters. As Fritz outlines in the module’s design document, the Threeler’s filter circuit emphasizes nonlinear resonances and is intended to be used creatively, rather than as an equalization module.

Threeler VCF

  1. Filter coarse frequency knob (sums with 2 and 3)
  2. Filter fine frequency knob (sums with 1 and 3)
  3. 1V-per-octave frequency input (sums with 1 and 2) (DC INPUT)
  4. Filter resonance knob (sums with 5 x 6)
  5. Filter resonance CV scaling knob (sums with 5, scaled by 6)
  6. Filter resonance CV input (sums with 4, scaled by 5) (DC INPUT)
  7. Filter series selector knob
  8. FM CV scaling knob
  9. Frequency Modulation (FM) signal input (DC INPUT)
  10. Filter input scaling knob
  11. Filter input (AC INPUT)
  12. Filter stage 1 output (AC OUTPUT)
  13. Filter stage 2 output (AC OUTPUT)
  14. Filter stage 3 output (AC OUTPUT)

Notes:

5Pulser Waveshaper

The 5Pulser Waveshaper, like the Wavolver II, is one of Fritz’s waveshaper designs inspireed by “West Coast” synthesizer modules by Tcherepnin and Buchla. The circuit is designed to take a sawtooth input and output pulse trains at different frequency combinations (set by switches). The resulting sound is an overdriven kind of effect. Like all waveshaper circuits, the 5Pulser is amplitude dependent, so a wide variety of effects can be acheived by using other input waveforms or sounds that change dynamically over time.

5Pulser Waveshaper

  1. Signal input (AC INPUT)
  2. Waveshaper output (AC OUTPUT)
  3. Waveshaping strength knob (sums with 4 x 5)
  4. Waveshaping CV scaling knob
  5. Waveshaping CV input (sums with 3, scaled by 4) (DC INPUT)
  6. Waveshaper harmonic switches

Notes:

Dual 2Q/4Q Multiplier

Fritz’s Dual 2Q/4Q Multiplier is a module that multiplies a pair of AC or DC signals for use as either a standard VCA (“two-quadrant”) or as a ring modulator (“four-quadrant”). A bias control allows for amplitude modulation effects such as tremolo. The module contains two identical circuits.

Dual 2Q/4Q Multiplier

  1. X signal input (AC or DC INPUT - set by 6)
  2. X signal scaling knob
  3. Y signal input (AC or DC INPUT - set by 7)
  4. Y signal scaling knob
  5. 2-quadrant / 4-quadrant mode switch
  6. X AC/DC switch
  7. Y AC/DC switch
  8. Signal output (AC OUTPUT)
  9. Y signal bias knob

Notes:

Mixer

The Mixer on the Fritz panels, like the Mixer on the Random*Source Serge, allows for the buffered scaling and mixing of multiple AC signals. On this Mixer module, four inputs can be mixed with attenuation knobs, and the module offers both a regular output and an inverted one with the signal 180-degrees out of phase.

Mixer

  1. Signal input 1 (AC INPUT)
  2. Input 1 gain knob
  3. Signal input 2 (AC INPUT)
  4. Input 2 gain knob
  5. Signal input 3 (AC INPUT)
  6. Input 3 gain knob
  7. Signal input 4 (AC INPUT)
  8. Input 4 gain knob
  9. Mixer output (AC OUTPUT)
  10. Inverted mixer output (AC OUTPUT)

Notes:

Panel 2 (Chaos Theory)

Ian Fritz Panel 2

Teezer TZFM VCO

The Teezer Through-Zero FM VCO is Fritz’s design for a sawtooth-core oscillator that can do true, bipolar (or “through zero”) frequency modulation, using an entirely analog signal path. Typical analog FM circuits were designed to create sonic effects ranging from vibrato to noisy, warped timbres using a second oscillator as a modulating source. These signals typically summed into the existing DC voltage chain controlling the oscillator’s frequency, meaning that they only modulated the oscillator in a positive direction. To generate “true” FM synthesis, as developed by John Chowning and most famously implemented on digital synthesizers such as the Yamaha DX7, the frequency of the primary oscillator needs to be able to go negative as well.

The Teezer VCO, by allowing for bipolar FM, can be used to synthesize sounds with the full repertoire of FM effects, including rich sidebands that behave in a nonlinear fashion that can be used to create brassy tones, bell sounds, and other rich, time-varying spectra. The VCO has outputs for triangle, sine, and sawtooth waveforms, and ten-turn precision dials can be used to set the base frequency of both the primary oscillator and the FM circuitry.

Teezer TZFM VCO

  1. Coarse frequency knob (sums with 2 and 11)
  2. Fine frequency knob (sums with 1 and 11)
  3. Sync scaling knob
  4. Sync signal input (scaled by 3) (AC INPUT)
  5. Linear FM scaling knob
  6. Linear Frequency Modulation (FM) input (scaled by 5, sums with 8) (AC INPUT)
  7. AC/DC switch for linear FM input
  8. Initial FM frequency knob (sums with 5 x 6)
  9. Exponential Frequency Modulation (FM) input (scaled by 10) (DC INPUT)
  10. Exponential FM scaling knob
  11. 1V-per-octave input (sums with 1 and 2) (DC INPUT)
  12. Triangle waveform output (AC OUTPUT)
  13. Sine waveform output (AC OUTPUT)
  14. Sawtooth waveform output (AC OUTPUT)

Notes:

4x4 AD/AR / Dual VCA / Mixer

The 4x4 (All-In Plus) Attack-Decay/Attack-Release is an extension to the All-In EG module, and in many ways is Fritz’s answer to the Serge Dual Universal Slope Generator - a multi-function circuit that can be used as an envelope generator, an oscillator, or a monostable delay. The module as designed by Akin also includes a Dual Voltage-Controlled Amplifier and a four-input Mixer.

The 4x4 AD/AR has four input modes and four output signals. A trigger/gate input will generate an envelope with an attack and decay (trigger) or release (gate) time set by the knobs. A manual trigger button can be used to generate an AR envelope as well. A pulse is generated at the end of the envelope, and a “cycle” switch allows the module to run as an oscillator either as an LFO or in the audible frequency range.

In addition, the module contains a pulse delay circuit, which can be used independently or to trigger the envelope generator. The delay is monostable, so a new trigger sent into the circuit before a delayed pulse is completed will reset the delay circuit.

The Dual VCA circuit consists of a pair of signal amplifier circuits with AC input and output, CV envelope input, and a bias control. The Mixer on this side of the panel has no attenuation knobs and will mix up to four input signals at unity gain, with regular and inverted signal outputs.

4x4 AD/AR

  1. Envelope delay time input (DC INPUT)
  2. Envelope delay time scaling knob
  3. Pulse width knob
  4. Pulse-to-EG enable switch
  5. Delayed pulse input (Pulse INPUT)
  6. Delayed pulse output (Pulse OUTPUT)
  7. Trigger/gate input (Pulse INPUT)
  8. Attack time knob
  9. Decay / release time knob
  10. Envelope CV output (DC OUTPUT)
  11. End-of-envelope trigger (Pulse OUTPUT)
  12. Cycle switch
  13. Manual envelope trigger button
  14. VCA signal input (AC INPUT)
  15. VCA CV input (DC INPUT)
  16. VCA bias knob
  17. VCA signal output (AC OUTPUT)
  18. Mixer input 1 (AC INPUT)
  19. Mixer input 2 (AC INPUT)
  20. Mixer input 3 (AC INPUT)
  21. Mixer output (AC OUTPUT)
  22. Mixer inverted output (AC OUTPUT)

Notes:

ChaQuO

The Fritz Chaos Generator and Quadrature Oscillator is designed to generate chaotic signals, defined by Fritz as “signals that have varying degrees of interesting irregularity without actually becoming random.” The circuit developed by Fritz uses a quadrature oscillator - which generates a sine and a cosine wave - to drive a circuit that simulates a double potential-well problem in quantum mechanics, which exhibitss chaotic behavior. The module outputs three chaotic signals as well as the raw and inverteed signals for the quadrature oscillator.

ChaQuO

  1. Chaos rate knob
  2. High/low frequency switch
  3. Chaos damping knob
  4. Quadrature oscillator coarse frequency knob
  5. Quadrature oscillator fine frequency knob
  6. Loop gain knob
  7. Drive scaling knob
  8. Drive CV input (scaled with 7) (DC INPUT)
  9. X-coupling strength knob
  10. X chaos output (DC OUTPUT)
  11. Y chaos output (DC OUTPUT)
  12. Z chaos output (DC OUTPUT)
  13. Sine quadrature output (AC OUTPUT)
  14. Inverted sine quadrature output (AC OUTPUT)
  15. Cosine quadrature output (AC OUTPUT)
  16. Inverted cosine quadrature output (AC OUTPUT)

Notes:

Dual TGTSH

The Dual Threshold/Gate/Trigger/Sample/Hold is a Fritz circuit that combines a sample-and-hold circuit with a trigger/gate output that actuates based on comparing a timing signal crossing a threshold. This allows you to use an LFO signal to sample a secondary signal, drive a sequencer, or trigger an envelope. The module contains two identical halves.

Dual TGTSH

  1. Threshold CV input (DC INPUT)
  2. Threshold CV scaling knob
  3. Threshold knob (sums with 1 x 2)
  4. Timing CV input (DC INPUT)
  5. Main CV input (DC INPUT)
  6. Gate output (Pulse OUTPUT)
  7. Trigger output (Pulse OUTPUT)
  8. Sample-and-hold output (CV OUTPUT)

Notes:

All-In EG

The All-In Envelope Generator is a simple attack-decay or attack-decay-release envelope generator that can be driven by a trigger/gate signal or, through a secondary circuit, by any input signal that crosses a positive 1.5V threshold. The DC input, in addition, runs through a monostable delay circuit, allowing an envelope to be triggered some time after a threshold event.

All-In EG

  1. Monostable delay CV/triggeer input (DC INPUT)
  2. Delay time knob
  3. Pulse width knob
  4. Delayed pulse output (Pulse OUTPUT)
  5. Envelope generator trigger/gate input (Pulse INPUT)
  6. Attack time knob
  7. Decay / release time knob
  8. Envelope signal (DC OUTPUT)

Notes:

Chaotica

The Chaotica circuit by Ian Fritz generates complex control voltages through a series of nonlinear elements that can be controlled independently via a variety of parameterss to create three chaotic CV signals.

Chaotica

  1. Chaos rate knob
  2. Chaos CV scaling knob
  3. Chaos CV input (scaled by 2, sums with 1) (DC INPUT)
  4. Gain CV input (scaled by 5, sums with 6) (DC INPUT)
  5. Gain CV scaling knob
  6. Gain knob
  7. Damping knob
  8. Damping CV scaling knob
  9. Damping CV input (scaled by 8, sums with 7) (DC INPUT)
  10. Offset CV input (scaled by 11, sums with 12) (DC INPUT)
  11. Offset CV scaling knob
  12. Offset knob
  13. Non-linear drive amount knob
  14. Reset trigger (Pulse INPUT)
  15. Tame/wild switch
  16. 1 eye / 2 eyes switch
  17. X chaos output (DC OUTPUT)
  18. Y chaos output (DC OUTPUT)
  19. Z chaos output (DC OUTPUT)

Notes:

4x4 AD/AR / Dual VCA / Mixer

The 4x4 (All-In Plus) Attack-Decay/Attack-Release is an extension to the All-In EG module, and in many ways is Fritz’s answer to the Serge Dual Universal Slope Generator - a multi-function circuit that can be used as an envelope generator, an oscillator, or a monostable delay. The module as designed by Akin also includes a Dual Voltage-Controlled Amplifier and a four-input Mixer.

The 4x4 AD/AR has four input modes and four output signals. A trigger/gate input with generate an envelope with an attack and decay (trigger) or release (gate) time set by the knobs. A manual trigger button can be used to generate an AR envelope as well. A pulse is generated at the end of the envelope, and a “cycle” switch allows the module to run as an oscillator either as an LFO or in the audible frequency range.

In addition, the module contains a pulse delay circuit, which can be used independently or to trigger the envelope generator. The delay is monostable, so a new trigger sent into the circuit before a delayed pulse is completed will reset the delay circuit.

The Dual VCA circuit consists of a pair of signal amplifier circuits with AC input and output, CV envelope input, and a bias control. The Mixer on this side of the panel has attenuation knobs and will mix up to four input signals, with regular and inverted signal outputs.

4x4 AD/AR

  1. Envelope delay time input (DC INPUT)
  2. Envelope delay time scaling knob
  3. Pulse width knob
  4. Pulse-to-EG enable switch
  5. Delayed pulse input (Pulse INPUT)
  6. Delayed pulse output (Pulse OUTPUT)
  7. Trigger/gate input (Pulse INPUT)
  8. Attack time knob
  9. Decay / release time knob
  10. Envelope CV output (DC OUTPUT)
  11. End-of-envelope trigger (Pulse OUTPUT)
  12. Cycle switch
  13. Manual envelope trigger button
  14. VCA signal input (AC INPUT)
  15. VCA CV input (DC INPUT)
  16. VCA bias knob
  17. VCA signal output (AC OUTPUT)
  18. Mixer input 1 gain knob
  19. Mixer input 2 gain knob
  20. Mixer input 3 gain knob
  21. Mixer input 4 gain knob
  22. Mixer input 1 (AC INPUT)
  23. Mixer input 2 (AC INPUT)
  24. Mixer input 3 (AC INPUT)
  25. Mixer input 4 (AC INPUT)
  26. Mixer output (AC OUTPUT)
  27. Mixer inverted output (AC OUTPUT)

Notes:

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CGS Panels

Black Swamp Serge panel

CGS Programmer-Sequencer panel

The Black Swamp and Programmer are Serge panels with a complex pedigree, consisting of a variety of sequencing and logic modules designed to create rhythmic CV and trigger patterns.

Ken Stone, one of Australia’s best-known synthesizer designers, developed a series of DIY modules in the late 1980s. Dubbed CGS (for Cat Girl Synthesizer), these were available as mail order kits and were among the first DIY synthesizer projects to be published on the World Wide Web. Many of the kits were licensed copies of Tcherepnin’s original Serge designs, and were for many years the only way to acquire Serge DIY kits. However, most of the modules were of Stone’s invention, and several (such as the Pulse Divider and Boolean Logic) were licensed and adopted in commercial Serge panels (including our Random*Source Serge).

Elby Designs is the Tcherepnin-licensed manufacturer of Serge kits and synthesizers in Australia. Founded by Laurie Biddulph (L B = Elby) in 2003, Elby manufactures and sells DIY kits for Stone’s CGS modules alongside licensed Serge modules in both 4U and 3U (so-called “EuroSerge”) format. Beginning in 2010, Biddulph began offering full panels of curated CGS modules under the moniker BoCGS (“Best of Cat Girl Synth”). One of these panels was called the Sequencer With Arbitary Manipulated Pulses (or SWAMP), and consisted of four CGS modules - CGS31 (Digital Noise), CGS13 (Gated Comparator), CGS36 (Pulse Divider and Boolean Logic), and CGS59 (Programmer-Sequencer).

In 2015, Jon Peters, a California-based DIY synth designer and builder, created and published a modified SWAMP design called the Black Swamp, which took Biddulph’s panel layout and Stone’s PCBs and added a variety of modifications and extra features, mounted onto a black (rather than silver) aluminum plate. A year later, Charlie Kerr at Loudest Warning - the Tcherepnin-licensed Serge manufacturer for the UK - did a limited edition run of fully built and tested Black Swamp panels; we have one of these panels.

Another of Stone’s designs, CGS359, is an update of Stone’s earlier Programmer-Sequencer (itself adapted from Tcherepnin’s Serge Programmer module), designed to be built out in an arbitrary number of stages. Our Programmer, built in 2020 by Finlay Shakespeare at Future Sound Systems in the UK as part of a limited run of panels, is a 16-stage version with a number of additional features.

The Black Swamp and Programmer are incredible examples of the iterative design made posssible by open-source, DIY synthesizer communities such as those working around the Serge modular format.

Black Swamp

Black Swamp panel

Boolean Logic

The unlabelled leftmost module on the Black Swamp is Ken Stone’s Boolean Logic module (one half of CGS36). One of his designs that is often incorporated in Serge panels, it was intended to expand on the comparator modules in the original Serge systems (such as the Triple Comparator on the 73-75 Serge). This version of the module consists of two submodules that set output voltages HIGH or LOW based on pairs of control voltage inputs:

Finally, a basic inverter at the bottom outputs the inverse of its input, acting as a NOT gate.

Boolean Logic

  1. Output for the AND comparator (Pulse OUTPUT)
  2. Input 1 for the AND comparator (Pulse INPUT)
  3. Input 2 for the AND comparator (Pulse INPUT)
  4. Output for the OR comparator (Pulse OUTPUT)
  5. Input 1 for the OR comparator (Pulse INPUT)
  6. Input 2 for the OR comparator (Pulse INPUT)
  7. Output for the inverter (Pulse OUTPUT)
  8. Input for the inverter (Pulse INPUT)

Notes:

Digital Noise

Ken Stone’s Digital Noise module (CGS31) differs from the standard Serge Noise source (as used in the SSG and Random Source modules) in a few important ways. First, it is a digital, rather than analog, noise source, which means that the oscillator core of the module is a pseudo-random digital pulse train generated by a phase-locked loop IC, a trio of XOR gates, and a shift register. This allows the module to provide filtered white and pink noise outputs, but also random gate signals and the ability to be externally clocked to generate random values at any frequency.

The Black Swamp version of the module has a number of modifications compared to the original, including two random gates instead of one, direct access to the internal oscillator clock, and the ability to operate at a much lower frequency (below .01Hz) to create slow random pulse trains / digital “dust” effects.

Digital Noise

  1. White noise output (AC OUTPUT)
  2. Pink noise output (AC OUTPUT)
  3. Random Gate 1 output (Pulse OUTPUT)
  4. Random Gate 2 output (Pulse OUTPUT)
  5. External clock input / internal clock output (Pulse INPUT / OUTPUT)
  6. Internal / external clock switch
  7. CV rate input for internal clock (DC INPUT)
  8. CV rate knob for internal clock (summed with 7)

Notes:

Pulse Divider

The Pulse Divider module (the second half of CGS36) is another of Ken Stone’s modules that appears regularly on Serge panels from other manufacturers (including our Random*Source Serge). The module takes a pulse input and outputs triggers on numerical subdivisions, allowing the user to have, e.g. a clock signal input generate a polyrhythmic output. The Black Swamp version of the module contains two additional switches as well as LED indicators for the subdivision outputs.

Pulse Divider

  1. Reset switch for the division counters on the module
  2. Pulse input for divider (Pulse INPUT)
  3. Outputs a pulse every 2nd pulse (Pulse OUTPUT)
  4. Outputs a pulse every 3rd pulse (Pulse OUTPUT)
  5. Outputs a pulse every 4th pulse (Pulse OUTPUT)
  6. Outputs a pulse every 5th pulse (Pulse OUTPUT)
  7. Outputs a pulse every 6th pulse (Pulse OUTPUT)
  8. Outputs a pulse every 7th pulse (Pulse OUTPUT)
  9. Outputs a pulse every 8th pulse (Pulse OUTPUT)
  10. “Syncopate” switch that resets the division counters every 7th pulse

Notes:

Gated Comparator

Ken Stone’s Gated Comparator (CGS13) is one of his more novel designs. In Stone’s words:

The idea for this project came when I was listening to some music in which part of the background was jumping between octaves in a semi-random fashion. Feeding noise into a comparator was my immediate thought, but I soon realized this wasn’t going achieve what I wanted. I needed to be able to control when these jumps could occur. As such, some form of memory element was required, into which the level could be clocked when required.

I have used an 8 stage digital shift register as the memory element. Each clock pulse, the remembered level (logic 0 or logic 1) is moved into the next stage “bucket brigade” fashion, and the new value stored in the first memory cell. The result is a random level (on or off) at a predetermined time at the first output, plus time delayed versions of previous levels across the remaining outputs.

At its core, the module takes in a CV input and a clock signal. When a clock trigger arrives, the CV signal is compared against a reference voltage, and sets the first stage of the comparator “high” or “low” (this is similar to the Onebang module on the Shelfisizer). The previous value for stage 1 is then shifted down to stage 2, the stage 2 value to stage 3, and so forth, giving 8 bits of comparator memory. These values can be used to trigger different modules elsewhere in the system; they can also be combined as bits in a “random” signal output and mixed together using the knobs next to each stage to create a CV output. The module also has functions for looping the recorded states.

Jon Peters made a number of modifications to the Gated Comparator on the Black Swamp, including the addition of an interface to manually load the comparator’s memory and a push-pull switch on each knob to bypass individual bits in the signal outputs.

Gated Comparator

  1. Loop enable switch - “on” disables new input signals at 11 from being loaded into memory
  2. Disable jack - a high gate signal will temporarily disable the loop and allow new input (Pulse INPUT)
  3. Load momentary switch - allows for the manual loading of the comparator at the bit set by the rotary dial 6
  4. Comp output - outputs the raw comparator value based on input 11 as a square wave / gate (Pulse OUTPUT)
  5. Loop input. When the loop enable switch 1 is on, this can receive a gate signal to set bit 1
  6. Rotary switch for manual loading - selects which bit the load switch 3 or the loop trigger 7 will load
  7. Loop load input for manually loading bits into the memory (Pulse INPUT)
  8. Range knob that acts as a master attenuator for the module’s CV outputs
  9. Sensitivity knob for the comparator threshold (adds to 16 x 10)
  10. Sensitivity scaling knob for CV threshold (multiplies with 16, adds to 9)
  11. CV input to the comparator (DC INPUT)
  12. Random output of the comparator - treats each stage as a bit in an 8-bit signal that is converted to noise (DC OUTPUT)
  13. Inverted random output - same as 12 but with the bit order flipped (DC OUTPUT)
  14. Mix output - the eight comparator states are scaled by knobs in row 19 and summed (scaled by 8) (DC OUTPUT)
  15. Inverted mix output - same as 14 with the signal inverted (scaled by 8) (DC OUTPUT)
  16. CV input for setting a varying comparator level (multiplied by 10, added to 9) (DC INPUT)
  17. Clock input to load the comparator and shift the bits (Pulse INPUT)
  18. Individual stage outputs of the shift register (Pulse OUTPUT)
  19. Attenuator knobs for each stage when sent to the CV outputs- pulling a knob will disable its bit from being used in either the mix (14 / 15) or random (12 / 13) outputs

Notes:

TRK / Programmer / Sequencer / Random / Vertical Sequencer

The final module in the Black Swamp consists of a heavily modified version of Ken Stone’s Programmer / Sequencer module (CGS59), itself a variant on the Tcherepnin’s original Sequencing Programmer modules, such as the Sequencer / Programmer on our Random*Source Serge.

Stone’s 8-stage Programmer / Sequencer consists of 8 stages of presets, with rows of knobs to set four values for each preset, similar ot the TKB. Unlike the R*S TKB and Sequencer / Programmer, however, the module has trigger inputs for each preset stage as well as outputs, allowing it to be used as a general-purpose recall system, as well as a conventional sequencer.

Jon Peters added substantial functionality to the Programmer / Sequencer in the original SWAMP, merging in a number of other CGS modules including a Sequential Switch and Quad Logic Gates, allowing for vertical sequencing and different behaviors of the gate outputs; a Noise module to allow for random sequencing; and an 8-pad Touch Responsive Keyboard (TRK), replacing the stage select buttons and allowing the module to be used as a keyboard in a manner similar to the TKB. In addition, he added expanded output voltage range to the preset knobs, along with a “solo” mode to allow three rows to remain sequencing while the fourth is controlled by the keyboard.

Programmer / Sequencer

  1. “A” row of CV knobs for each preset stage. Pulling a knob out puts the column into high range mode.
  2. “B” row of CV knobs for each preset stage
  3. “C” row of CV knobs for each preset stage
  4. “D” row of CV knobs for each preset stage
  5. Gate outputs for each stage of the sequencer (Pulse OUTPUT)
  6. Stage select inputs for each preset stage (Pulse INPUT)
  7. Three-way select switch for each stage’s gate output behavior - the right position causes the gate to last for the duration of the clock pulse; the center position causes no gate to be output; the left position starts the gate output when the clock pulse goes low
  8. Three-way switch for the stage’s behavior when selected by an “up” sequence trigger - the down position causes the stage to run, which outputs its preset values; the center position sets the stage to stop, halting the sequencer until it is reset; the up position sets the stage to skip to the next preset in the sequence
  9. Three-way switch for the stage’s behavior when selected by an “down” sequence trigger - the down position causes the stage to run, which outputs its preset values; the center position sets the stage to stop, halting the sequencer until it is reset; the up position sets the stage to skip to the next preset in the sequence
  10. Capacitive touch pads (the “keys”) for the TRK - touching a key selects its corresponding stage
  11. CV output for the “A” row of presets (DC OUTPUT)
  12. CV output for the “B” row of presets (DC OUTPUT)
  13. CV output for the “C” row of presets (DC OUTPUT)
  14. CV output for the “D” row of presets (DC OUTPUT)
  15. “ABCD” 32-stage output, caussed by wrapping through the rows, with the reset row selectable by switch 16 (DC OUTPUT)
  16. Reset selection switch for the vertical clock, allowing the user to select whether output 15 wraps through two, three, or all four rows on the sequencer
  17. Momentary toggle switch to reset the vertical clock
  18. Trigger output for the TRK - sends a pulse when a key is pressed (Pulse OUTPUT)
  19. Gate output for the sequencer - sends combined gate values based on the settings of each stage’s switch 7 (Pulse OUTPUT)
  20. Random input - causes the sequencer to jumb to a random position (Pulse INPUT)
  21. Up input - pulses will advance the (horizontal) sequencer to the right (Pulse INPUT)
  22. Down input - pulses will advance the (horizontal) sequencer to the left (Pulse INPUT)
  23. CV output for key “pressure” on the TRK - in reality, this corresponds more to the surface area of the pad covered by finger contact than actual pressure (DC OUTPUT)
  24. Gate output for the TRK - sends a high value as long as a key is pressed (Pulse OUTPUT)
  25. Solo mode switch - in solo mode, rows A, B, and C are sequenced while row D is controlled by the TRK
  26. Stop input - a high voltage at this jack will disable the sequencer and park it at the “ghost” stage - CV outputs will continue at their last value (Pulse INPUT)

Notes:

Programmer

CGS Programmer panel

The CGS Programmer, like the Serge TKB, is a 16-stage combination sequencer / preset manager with four rows per stage. Unlike the TKB, the Programmer has no keyboard, and instead can trigger stages by manual buttons (like the R*S Sequencer / Programmer) or by trigger inputs available for each stage. Like the Programmer-Sequencer in the Black Swamp (also based on Stone’s core Programmer design), the Programmer has Run/Skip/Stop functionality for each stage, as well as trigger inputs for seqeuencing in either direction.

CGS Programmer panel

  1. Gate outputs for each stage of the sequencer (Pulse OUTPUT)
  2. Trigger selection switch for each stage - enabled will cause the stage to also output a trigger at 17 when selected
  3. Stage select inputs for each preset stage (Pulse INPUT)
  4. “A” row of CV knobs for each preset stage
  5. “B” row of CV knobs for each preset stage
  6. “C” row of CV knobs for each preset stage
  7. “D” row of CV knobs for each preset stage
  8. Three-way switch for the stage’s behavior when selected by an “left” sequence trigger 12 - the up position causes the stage to run, which outputs its preset values; the center position sets the stage to stop, halting the sequencer until it is reset; the down position sets the stage to skip to the next preset in the sequence
  9. Three-way switch for the stage’s behavior when selected by an “right” sequence trigger 11 - the up position causes the stage to run, which outputs its preset values; the center position sets the stage to stop, halting the sequencer until it is reset; the down position sets the stage to skip to the next preset in the sequence
  10. Preset selection buttons for each stage
  11. Right input - pulses will advance the sequencer to the right (Pulse INPUT)
  12. Left input - pulses will advance the sequencer to the left (Pulse INPUT)
  13. CV output for the “A” row of presets (AC OUTPUT)
  14. CV output for the “B” row of presets (AC OUTPUT)
  15. CV output for the “C” row of presets (AC OUTPUT)
  16. CV output for the “D” row of presets (AC OUTPUT)
  17. Trigger output for the TRK - sends a pulse when a stage is selected and that stage’s selection switch 2 is enabled (Pulse OUTPUT)
  18. Push output for the programmer - sends a high value as long as a button is pushed (Pulse OUTPUT)

Notes:

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The Shelfisizer

2019 Shelfisizer Shelfisequencer

The Shelfisizer is an open-source project by Luke DuBois inspired by Serge modular systems but also hybrid analog synthesis / microcontroller systems such as the Buchla 200e. These modules use 16mHz Adafruit Metro Mini microcontrollers and simple monolithic IC chips to handle much of the logic that definies the module’s behavior, leaving discrete components for the parts of the modules that actually generate analog signals. The use of microcontrollers makes it simple to prototype modules that require an understanding of “state”, such as pattern memory or hysteresis, and the use of CMOS ICs allows for a design that has a much lower part count than typical analog synthesizer modules.

Shelfisizer designs, including microcontroller software, circuit diagrams, and panel graphics can be found on the Shelfisizer GitHub page.

2019 Panel

Shelfisizer 2019

Pulse

The Pulse module on the Shelfisizer is a 16-stage, 4-row sequencer with boolean (on/off) states for each stage of each row. The Arduino in the module saves the current sequence as long as the module has power, and a 4-button interface allows you to dynamically program in patterns for the 4 output rows, as well as a numbe of other functions. The module generates pulses in response to an external clock which advances the current step in the sequence.

Pulse

  1. “A” sequence (Pulse OUTPUT)
  2. “B” sequence (Pulse OUTPUT)
  3. “C” sequence (Pulse OUTPUT)
  4. “D” sequence (Pulse OUTPUT)
  5. “Page” button
  6. “Select” button
  7. “Up” button
  8. “Down” button
  9. External clock (Pulse INPUT)
  10. Interface LEDs

Notes:

Onebang

The Shelfisizer’s Onebang module generates rhythmic output by comparing up to six input voltages (labeled as A-F) against a threshold, sending out pulses on a clock input. There are 12 modes of operation, which change the way in which the input voltages generate pulses.

Onebang

  1. CV inputs A-F (DC INPUT)
  2. Trigger outputs A-F (Pulse OUTPUT)
  3. External clock (Pulse INPUT)
  4. Mode button
  5. Mode indicator LEDs

Notes:

Dust / Dirt

The Dust / Dirt module is the one part of the 2019 Shelfisizer that generates AC voltage (“audio”). It has two modes, allowing it to act either as a pulse triggered, noisy 6-voice drum machine (DIRT), or as a six-channel noise generator with specific characteristics for each channel (DUST).

Dust / Dirt

  1. Trigger inputs for each channel (Mode 0 only) (Pulse INPUT)
  2. Drum / noise outputs for each channel (AC OUTPUT)
  3. Knobs to control channel parameter
  4. LFO rate knob
  5. LFO depth knob
  6. Mode switch

Notes:

Lookup

The Lookup module contains a circle of 16 preset knobs (numbered 0-15) that can be accessed by three independent channels of input voltage (A, B, and C). The input voltage switches which preset voltage will appear at the output using a 74HC4067 CMOS multiplexer, making the module work like a sequencer that can be arbitrarily indexed by control voltage. Two mode switches allow for four different behaviors from the module.

Lookup

  1. CV inputs for channels A, B, and C (DC INPUT)
  2. Preset voltages for channels A, B, and C (DC OUTPUT)
  3. Preset value knobs 0-15.
  4. Mode switch 1.
  5. Mode switch 2.
  6. LED display to show which preset knob is currently being output on which channel. This is a 4-bit display in Gray code.

Notes:

Square

The Square module is a simple, six-channel “square up” circuit using LM393/LM339 comparators. Any positive AC voltage input will be raised to 5V, with negative voltages pulled up to 0V.

Square

  1. Voltage inputs 1-6 (AC INPUT)
  2. “Squared-up” outputs 1-6 (Pulse OUTPUT)

Notes:

Shift

The Shift module is a dual, 4-stage Analog Shift Register, inspired by the 1975 Serge ASR and borrowing a low parts count sample-and-hold design by Chris McDowell for each stage.

An analog shift register functions as a cascading sample-and-hold, where a sampled input voltage appears at the first output; when a new voltage is sampled, this first voltage moves to the second output, while the new voltage appears at the first output, and so on. The Shift module uses LF398 sample-and-hold ICs with polypropylene hold capacitors. It has four stages on two sides (L and R), which can be combined for an eight-stage system. Tcherepnin’s ASR was, along with the ÷N COM, one of his most obviously “musical” designs, as the cascaded outputs could be patched to different oscillators to create pitch delays, canons or so-called “Arabesque” melodies.

Shift

  1. CV input to be sampled (DC INPUT)
  2. Sample trigger (Pulse INPUT)
  3. “Carry” pulse (Pulse OUTPUT)
  4. Manual trigger button
  5. ASR stage 1 (DC OUTPUT)
  6. ASR stage 2 (DC OUTPUT)
  7. ASR stage 3 (DC OUTPUT)
  8. ASR stage 4 (DC OUTPUT)

Notes:

Shelfisequencer

Shelfisequencer

Shelfisequencer

The Shelfisequencer is a three-row trigger/gate sequencer panel, modeled after the original 1973 Serge “gate” sequencer and successive designs by Ken Stone. The panel has three trigger inputs and three CV inputs which, depending on the selected mode of operation, allow it to be used as a standard step sequencer or a CV-controlled triggering device, with three different firing patterns. The red and white jacks on the right send out 5 volt pulses in turn - by stacking banana cables in the outputs you can design complex rhythmic patterns.

Shelfisequencer

  1. Trigger inputs for rows A, B, and C (Pulse INPUT)
  2. CV inputs for rows A, B, and C (DC INPUT)
  3. Three-way mode switch 1 (Gate, trigger, unique trigger)
  4. Three-way mode switch 2 (Index, direct drive, direction)
  5. Three-way mode switch 3 (Horizontal scroll, regular, vertical scroll)
  6. Sequence stage outputs (Pulse OUTPUT)
  7. Reset button

Notes:

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