Electronic – How to split audio signal into 3 separate channels

audiocircuit-designsignal

I have been working with the following circuit:
enter image description here

to build a audio mixer where you can take multiple line inputs, cd players, computer, phone, synthesizers, etc… and mix them together to a single stereo "master" out.

The "master" out can be a power amplifier or powered speakers. So far tested powered speakers and works good and I expect this to work with "professional" grade amplifier/speakers. I.e: Mackies, Adams, Bryston etc… I will test with as much gear I can get my hands on…

So what I want to do is split the "master" out to 3 outputs: master, room and record and each with their own volumes.

  1. I'm thinking of taking R8A, R8B (the master POT) and replacing with a regular 22K resistor.
  2. Split the stereo signal after R9 and R10 and add 3 22K POTs there
  3. Finally line to 3 separate "stereo" jacks/channels

I'm going to do some testing. But I don't have enough gear to test it all, I'm thinking it will be ok so long the input impedance of the destination devices is bigger enough then the total out?

Does my plan sound sane or do you think I should add buffers to each of the split signal?

Update:

Pots are log.

Sample impedances:

Update 2:

Using TL072 as the op-amp.

Best Answer

1) Since users are pretty good at finding the weak point in any design, I'd recommend just using a buffer for each channel (yes that's 6 total opamps but they're cheap). For example, what if a user wants to temporarily disconnect your high impedance equipment to check the sound using their nice low impedance headphones?

2) High output impedance (compared to a low impedance buffered output) will make your transmission line more susceptible to noise, so if you're using high end equipment you're not doing yourself any favors by skimping on the output stage as long as you choose a decent quality opamp.

My recommendation would be to move your master potentiometer to the output of the summing stage (instead of R9 and R10), and splitting that into three different paths to feed each buffer opamp circuit. I think it would be a good idea to put a medium sized resistor (10k??) between the master potentiometer wiper lead and each buffer input too, that way the buffers don't interact with each other.