Quantity: 2

About Ken Stone’s CGS 75 VCS:

This is a licensed adaptation of the classic Serge DTG/DUSG

The Serge VCS module released in conjunction with from bananalogue.com is an extremely versatile control voltage generator and audio source. In the early 1970s, Serge Tcherepnin developed the Positive Slew and Negative Slew modules for the original Serge synthesizer. In time these merged into the classic Dual Universal Slope Generator. The Bananalogue VCS and CGS75 are an adaptation of Serge’s original circuit with a few new features.

The VCS is a unity gain voltage follower. The rising and falling slopes are independently and jointly voltage controllable over a wide range.

VC Transient Envelope Generator

A pulse at the trigger input will start the envelope, or a gate input will sustain the level and the envelope will fall when the gate goes low. Rise and fall are independently and jointly voltage controllable, with variable linear and exponential wave shapes.

VC Portamento

Voltage is slewed according to the rise and fall times.

VC LFO

When the cycle switch is thrown, the trigger input is connected internally to the end trigger output, creating a VC clock with variable waveform and independent rise and fall times.

VC Oscillator

While not as wide ranged, or accurate as a dedicated oscillator module, the VCS is still an excellent audio source. The Exp CV input is scaled approximately to the 1v/oct standard. The Output wave can be swept from triangle to saw with linear and non-linear waveforms. End Out also produces a pulse waveform.

VC Non-Linear Audio Processor (Low-Pass Gate)

If an audio rate signal is slewed, the module responds like a VCF, and a rough VCA. The signal is low-pass filtered down to silence, similar to a low-pass gate.

Envelope Follower

Positive and negative peak detection envelope follower.

VC Pulse Delay

Trigger input starts the envelope and a trigger will be produced again at the End Out when the envelope completes its cycle.

Sub-Harmonic Generator

If a series of triggers are applied to the VCS faster than the total rise and fall times, the module will divide the incoming signal by a whole number. In the audio range the output will be the sub-harmonic series.

I used the Bridechamber panel and a 2-pot Bridechamber bracket which fits the board out of the box.  I am especially happy to have these, because I am lucky enough to have used a Serge in the seventies and experienced the Negative and Positive Slew modules and the Dual Univeral Slope Generator.

I took the trouble to gain-match the NPN and PNP transistors in the lag processor, using a simple technique I found in Electronotes.  The 2N3904 pair are matched with each other and likewise for the 2N3906 pair.  Don’t know how important this is, but it couldn’t hurt.

Here’s a photo of my VCS assembly.  I ran a #20 stranded wire out from the power connector to the ground bus on the jacks.  I used twisted pair for most of the inputs and output, grounding the black wire back only at the jack, since there are but two grounds available on the board and those are dedicated to pots.