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I'm currently working on an audio circuit.

I'm using a simple mixer to mix two audio signals together. It works well enough for now.

Here is the circuit :

schematic

simulate this circuit – Schematic created using CircuitLab

Yet, I would like to be able to have an unmodified version of my in1 signal.

  • Maybe this is because I'm a newbie, but am I wrong to consider that this circuit makes it impossible to keep my in1 signal intact?
  • Do I need to split it before mixing it or use a more complex mixer?
  • Is there an easy way to do that?
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  • \$\begingroup\$ That's a pretty poor way of mixing. A summing amplifier would be better and if you use a quad opamp you could use two of those to buffer your input signals first, making the question moot. \$\endgroup\$ – Unimportant Feb 4 '19 at 11:20
  • \$\begingroup\$ @Unimportant what op amp would you use for a simple buffer/unity gain circuit ? \$\endgroup\$ – Vincent Perez Feb 4 '19 at 16:16
  • \$\begingroup\$ I'd use a ne5532. Because that used to be the go to audio opamp and I have a lot of them. There's probably some better ones out there by now tough. \$\endgroup\$ – Unimportant Feb 4 '19 at 16:32
  • \$\begingroup\$ @Unimportant I'll try to get my hands on some to test it out. I might have TL072 lying around, would that be ok ? \$\endgroup\$ – Vincent Perez Feb 4 '19 at 17:26
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Just take the signal from where you have put your in1 label. Audio signals are typically very low impedance, much lower than your 4.7 k divider. The divider will not affect in1 in any significant way, so the signal at the in1 point should remain as it were before modification.

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You could try something like this:

Op amp summing mixer

You said you want it "intact", this will invert it but you can always add another simple inverting amplifier stage at its output.

You will have less loss this way and you can even apply gain if you want to (determined by Rf/Rin). If you add a potentiometer for each input, you'd have individual volume control for each one. You can add more inputs if you like as well.

Hope this helps!

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