Quad Voltage Controlled Amplifier Board

From MMM Wiki

Jump to: navigation, search

Qua VCA PC board

The Quad VCA is designed as a utility module for providing four basic VCA's to be grabbed for a patch.

If wired according to the wiring chart, the four identical VCA's include:

Channel input: The VCA's are DC coupled to allow for signal processing of CV or audio signals.

CV input: The amplifier stage responds to a 0 to 5V control voltage.

         5V for full output. 0V for fully attenuated.
         All of the CV inputs are cascaded. 

The CV applied to channel 1 will control the gain of all four VCA's. Inserting a CV into another CV input will interrupt the cascade and apply the new CV to the selected and subsequent channels. No CV input will allow the internal reference to control the maximum user-set gain on channels prior to the first CV input.

Level control: Allows for adjusting the gain stage of the channel from 0 to maximum gain. On-board trimmer potentiometers allows for the user to adjust the maximum output gain for each channel up to just below the power supply limits. The level control is an input signal attenuator.

The trim pots on the left from top to bottom:

Top: Channel 2 level trim

2nd down: Channel 1 level trim

3rd down: Channel 4 level trim

Bottom: Channel 3 level trim

The channel trim is set first using a 5VDC reference inserted into the channel CV input and a reference waveform or voltage inserted into the channel input with the panel level control turned fully CW. All four channels can be set for whatever gain the user desires up to the limits of the power supply.

With no CV inputs, the internal gain level is set using the same channel input reference and adjusting the trim pot on the upper right for the desired gain.

This allows for the user to use the Quad VCA as a true Voltage Controlled amplifier if desired compared to a typical VCA which most people refer to as Voltage Controlled attenuators. With the internal reference increased, each channel can independently be used as a preamp for weak signal levels. Higher channels can still be selected as a unity-gain VCA by patching in a CV to the CV input.

I was factory calibrating them for unity gain on the first 6. Now, I set the Channel trim for unity gain and the internal reference for a gain of 1.5x.

Channel output: Output jack for the channel.

Wiring information:


Click for Adobe PDF version.


This module is available


To order, visit the MMM Store

Go to board dimensions and mounting

Go to general wiring conventions information

Back to DIY main menu

Personal tools