Serge Modifications and Enhancements
Dual Universal Slope Generator (DSG) :
The Dual Universal Slope Generators (DSG) from Serge Modular Music Systems are the ultimate patch programmable voltage generators: they are slew limited unity gain voltage followers whose positive and negative slewing rates are voltage controllable in an exponential manner.
Two VC inputs are provided, one calibrated at 1Volt/oct ,the other being fully adjustable in the positive and negative direction: this input can be switched to control either the positive or negative slope or both.
The DSG is a sort of "Universal module" which can be patched within itself to perform various tasks :
1. VC AR (or ASR )Transient Generator: the transient , with or without sustain level, may be started by a trigger or gate applied at the input.
2. VC LFO: the waveform is voltage controllable from saw to triangle.
3. VC Timing Pulse Generator.
4.VC Portamento Device.
5. Envelope Follower (Detector) with positive or negative detection.
6. VC Pulse Delay (Monostable)
7.Sub-Harmonic Series Generator
8. Audio Generator : from 0.1 Hz to 4000Hz with variable shape symmetry from saw to triangle.
9. Non-Linear Low Pass Filter.
Modifications and Enhancements to the DSG:
By adding two new switches to the module, the DSG becomes much more versatile for 'Live' performance and replaces advantageously one small patchcord.
Switch 2 : is an ON/OFF toggle switch which connects the 'END' to the 'Trigger IN' banana jacks .
What it does :When in the 'ON' position, the DSG oscillates and becomes a LFO or an Audio oscillator . Also, the 'END' output can be used as a Sequencer Clock
Switch 3: is an ON/OFF toggle switch which feeds back the "Output "signal into the "VC Input" banana jack.
What it does : The feedback transforms the "Attack"or "Release" (or both ) section of a linear transient signal (see Example A) into an exponential or logarithmic one.
For example, with the VC potemtiometer turned clockwise (+), one can obtain exponential style AR(Attack/'Release ) envelopes 'such as the ones used in percussive instruments (see Example B) . Similarly, with the VC potemtiometer turned counter -clockwise(-), one can obtain logarithmic style AR (Attack/'Release ) envelopes such as the ones used in Brass Envelopes (see Example C ).
Serge Modular Music Systems, is manufacturing a module called "Wave Multiplier (VCM): it is a sort of Wavetable generator entirely Voltage Controlled that you insert between the VCO's and the VCF in a patch. In general, Wave Multiplier affects the 'timbre' of a sound dramatically : They are used to dynamically process the sine input waveforms to produce new harmonically-related overtones. There are three different Multipliers per module :
-the upper section(VCM1) functions as a standard VCA, but with the switch toggled to 'High' the sine waveform input is "clipped" at the output. This is not the same as a simple comparator squaring function : there is a rounded flattening of the signal peaks - an effect somewhat similar to overdriving a tube amplifier - and, of course, this process is voltage controllable.
-the middle section (VCM2) provides a sweep of the odd harmonics (1,3,5,7,9,11, 13) when a sine wave is applied to its input and the knob is turned up or a CV is swept from low to high (This effect is similar to overblowing a wind pipe closed at one end). This module can also be used to produce the sound of various wind instruments. A second input is included ,to allow two signals to be mixed before processing. The VCM2 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 lower section(VCM3), performs a non-linear waveshaping known as "full wave rectification" but with sophisticated level-compensating conditioning as well. Indeed, 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 (2,4,8). As many other partials are present in the sound, the sonorities are rich and varied. A notable feature of this multiplier is that the full wave rectification is not accompagnied by a reduction in the output amplitude. There are two inputs to provide mixing before processing, and two outputs (One output is the 'squared up version of the other: the effect ressembles VC Pulse-width modulation but much more interesting.
Modifications and Enhancements for VCM modules:
Regretfully, the VCM does not provide any attenuation of the VC inputs at all . If you want to have a much subtiler control of the multiplier's range, proceed as follows :
Drill two 1/8" inch holes in the middle of the panel to accomodate the two VC input banana jacks (Use the old pre-drilled holes for the 10KLin potemtiometers you are going to add).
Multiplier n° 2 (Middle) :Connect the VC Input banana jack wire to the input of a 10KLIN Attenuation potemtiometer (P3) and the 'wiper output ' of the potemtiometer to the old VC input banana jack solder point. on the PCB.
Multiplier n°3 (Lower) : use the same procedure to add new potemtiometer P5.
(Excerpts of Chapter 3 and 4 of my tutorial " The Art of Analog Modular Synthesis By Voltage Control" , Copyright 1997 by André C. Stordeur - All Rights Reserved).