Dual and Quad Voltage Controlled Amplifier and Mixer

This project has been discontinued.

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

This 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 with low noise and 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 you have in this module 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.

Each VCA can be either direct coupled (DC) or high pass filtered (AC). The former allows DC and low frequency signals to be processed. While the latter provides a DC block to process only alternating audio frequencies.

To allow all the functions required by this module we have had to reduce the spacing between the pots. Instead of our usual 1.625" (41.3mm) we have opted for the smaller 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 26mA per rail.

The PCB is 99mm (deep) x 123mm (height). The four pots are normally board mounted for speed and simplicity

As with all Oakley projects the PCB is double sided with through plated holes, has tough solder mask both sides, and has bold component legending for ease of construction.

The issue 2 Oakley Dual VCA 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 BUSS connector that joins this module to another Dual VCA board to create the Quad VCA.

Project Downloads

Builder's Guide for issue 2 PCBs

Builder's Guide for issue 1 and 1.1 PCBs

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

Use 'save as...' button to download and view the files. IE users need to right hand mouse click and then choose 'save as'.

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

5U format 1U wide Dual VCA module in traditional black (old design)

5U format 2U wide Quad VCA module in traditional black (old design)

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: May 05, 2020.