Dual and Quad Voltage Controlled Amplifier and Mixer

PCBs for this project have been discontinued

The suggested front panel for the double width Oakley Quad VCA with 20mm control knobs.

This voltage controlled amplifier (VCA) module can be built either as a single width two channel VCA or a double width four channel VCA. Each VCA stage is identical and each features a high quality analogue VCA based around the 2164 chip with very low noise and very low CV breakthrough.

If the output socket of any VCA channel is unused then that signal will be mixed with the output of the final channel. That is, in the four channel version this module can be used as a four channel voltage controlled mixer. However, any VCA channel can simply be taken out of the mixing process by inserting a jack lead into its respective output socket.

Each VCA has two controls. Firstly, there is GAIN, a fixed bias to set the initial gain of the VCA, it can also be used a volume control. Secondly, the CV pot allows you to alter the sensitivity of the external CV that controls the VCA's gain. The pot is a 'reversible attenuator, so you are able to control not only the depth of the modulation but also the polarity. With the CV pot set straight up no CV signal reaches the VCA. With it fully right the CV is applied so that positive CVs increase the gain of the VCA. With the pot fully left then increasing positive CVs reduce the gain of the VCA. A single D-VCA module can used to crossfade between two signals, or pan one signal to either the left or right audio output.

Each VCA can be set with its front panel switch to respond either as a standard linear VCA, an exponential VCA, or with the switch in the middle position, as a mixture of the two responses. Each VCA is direct coupled and can therefore process CVs and audio signals.

The spacing between the pots is our smaller standard of 1.375" (34.9mm). Used in conjunction with smaller 20mm (13/16") diameter knobs this still allows for an attractive module design and finger friendly tweaking.

The suggested front panel for the single width Oakley Dual VCA with 20mm control knobs.

Power (+/-15V) is provided to the board either by our standard Oakley 4-way header or Synthesizers.com header. Current consumption is approximately 35 mA per rail.

The PCB is 85 mm (deep) x 124 mm (height). The four pots are normally board mounted for speed and simplicity. The main PCB is a four layer design with through plated holes, tough solder mask both sides, and bold component legending for ease of construction.

The Oakley Dual VCA built with the issue Dual VCA-X board as a single width MOTM format module in a natural finish Schaeffer panel. Note also the use of the optional Sock6 socket board to help keep the wiring to the sockets neat and tidy . The unfitted 2 x 5 IDC header at the bottom of the board is the BUS connector that joins this module to another Dual VCA board to create the Quad VCA.

Project Downloads

Builder's Guide

Dual and Quad VCA User Manual

Construction Guide Our handy guide to building Oakley DIY projects

Parts Guide Our handy guide to buying parts for Oakley DIY projects.

Schematics are only available to purchasers of the PCB(s) and will only be sent via e-mail when the board(s) are shipped.

Front Panel database

A Schaeffer front panel can be made for this module. The databases can be found by downloading the following links:

5U format 1U wide Dual VCA module in traditional black

5U format 2U wide Quad VCA module in traditional black

5U format 1U wide Dual VCA module in natural finish

To read, edit and print these files you will need a copy of 'Frontplatten Designer' from Schaeffer. Panels can be ordered via the program using its secure online ordering system.

Schaeffer are based in Berlin, Germany and can send panels to anywhere in the world. Delivery to the UK normally takes around ten days. For North American users you can also order your Schaeffer panels from Front Panel Express.

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Copyright: Tony Allgood.
Last revised: February 12, 2024.