Powering a DIY active audio mixer

Thread Starter


Joined Jan 24, 2016
Hi, everyone. I want to make a 3.5mm audio mixer so I can input from my guitar amp and my computer to my computer speakers. I found a description of one on http://www.circuitlib.com/index.php/tutorials/product/39-how-to-build-an-audio-mixer
with a few useful schematics.

The above picture shows the overall mixer. I'm going to skip the tone control modules. I'm planning on breadboarding everything so I can add them later if I want. For now I only want input modules and the summing amplifier.

This is a picture of an input module with separate left and right channels.

And this is the summing amplifier.

I've got a few questions, mostly related to powering the op-amps. In both modules of interest, each op-amp only has one power channel shown. Should I assume that every op-amp has both +15V and -15V power lines, each grounded through a 100nF capacitor?

I'll need a +-15V power supply. Can anyone recommend something cheap? If not, I was thinking I could invert a +15V line from a standard 15V adapter with an op-amp and leave ground alone. Would that be noisy?

To split 3.5mm to left and right channels, can I just make contact at the tip and the middle section? Do I need audio ground for anything?
Last edited:

blocco a spirale

Joined Jun 18, 2008
U2A and U2B are in the same package so the representation is correct; each package requires +15V and -15V.

How about powering it with one of these, it looks like a good implementation and is suitable for your application:


You will also need a small 2x18V transformer to go with it, 10VA should be ok.

You must use the audio ground, it is the return path for the audio signal.

Last edited:


Joined Aug 1, 2013
If you look at the LM833 datasheet, you will see that it is a dual part. There is no "standard" way to show a single power connection to a multi-stage component on a schematic like a dual or quad opamp. The first schematic has an error. U2B should be marked U1B, the other half of U1A on the schematic.