Quad channel volume control

Hi folks,

I've finished and testet the first prototype of my 4-channel volume control. It is designed to be used in my 4-way active speaker project, but can be used for any other project. It features optocouplers for the digital control connection to decouple the circuit from the controller.
It uses a PGA4311 and a OPA1664 input buffer. No output buffer is used, because the circuit should be located near the power stage.


Control has been tested from an Arduino and from the RaspberryPi - both work well. I'm thinking about a specific controller board designed just for this project.

Any comments?


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I'm not sure about the power supply. For the tests I'm using a small LM317/LM337 based supply: SimplePower | Crazy Audio. Right now I'm creating a similar circuit with an integrated mains transformer and 100mA LM317L/LM337L which are powerful enough for this circuit (it uses < 20mA).

The Optocouplers are standard KB817 compatible. They are rather slow, but for this application that doesn't matter. Data traffic are only 32 bit per volume change. With the current configuration they should work up to 10-30kHz, but I'm using 1kHz at the moment to be on the safe side.
For remote control using an mobile device, you could use the Raspberry Pi as an interface. The code to control this device from a Raspberry is just a few lines of Python code. A web app to change the volume should be not a big deal. Is anybody interested in it?
Here is the code to control it from a Raspberry Pi:
Controlling QuadVol with the Raspberry Pi | Crazy Audio