Schematics / VCA-Mixer
VCA/Mixer by Nyle Steiner visit the Synthasystem page for more info on construction , calibration and pcb offer http://user.xmission.com/~dingebre/Project.html ,from the original Synthasystem manual :
Audio signals are fed into inputs one, two and/or three, and levels of relative mixing are set with the three input pots.
The overall gain can be controlled by adjusting the pot labeled GAIN and or by feeding control voltages into the V.C. input jacks.
For use in conjunction with the envelope generator, use the following steps.
Plug the audio signal (from one of the oscillators) into one of the VCA Mixer inputs and turn up the pot for that channel about half way. Feed the out jack into an audio amplifier, guitar amplifier, or whatever sound system is being used. Turn up the master GAIN pot until a signal is heard. Turn the envelope generator output level pot for Env #1 all the way down. Turn the GAIN pot on the VCA Mixer counterclockwise until the audio signal just barely disappears. Turn the output level pot on the Env Gen #1 to about 12 o'clock. Now a signal should be heard in accordance with the setting of Env. Gen. #1 whenever a KBD trigger or other trigger is fed into the trigger jack of the envelope generator.
Envelope generators #2 and #3 can be used to control other modules while #1 is controlling the VCA Mixer. For example, to sweep the V.C. Filter and/or Ocs. Frequency.
On final note: Overdriving the VCA Mixer overrides control voltage rejection. You should keep the control voltage pot at about the 12 o'clock position, generally. Lack of control voltage rejection makes a "popping" sound.
Synthasystem subforum : http://www.electro-music.com/forum/index.php?f=189