So basically, I designed a mixer panel for monitoring my band when we play live. However, some of us play with a stereo in ear monitoring system and some of us use a mono speaker by their feet. I don't want things that are panned to the right not to be heard on the mono speakers when they are connected to the left output.

This means I need my mixer to have a mono/stereo switching system. I'm not sure if I want to use switched jack ports to have it automated. If I want that, how do I do that?

The other option is to make a button to switch the system to mono or stereo. This schematic I made very quickly and not very clean will do that? Or will it not mix both channels to the left output correctly? Schematic


2 Answers 2


Your scheme is overly complex. First of all, the left input is always connected to the left output, regardless of the switch position, so you might as well just connect them directly.

And there's no reason not to leave the right input connected to the right output even if you're not using it, so just wire that through, too.

So the whole thing boils down to a single SPST switch that shorts the left and right channels together.

However, this might be a bad thing if whatever's connected to Lin and Rin have low source impedances, so it might be a good idea to include some series resistance between each of those jacks and the switch. The value of resistance required would depend on the load impedances connected to the output jacks, which you haven't mentioned.

An even better approach would be to add some unity-gain buffers between the switch and the output jacks. Then the resistance used for mixing won't depend on the load impedance.

The whole thing ends up looking like this:


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ The mixer already has opamps just before the output jacks. The input source is line level, since this mixer is supposed to get input from insert ports on the mixer that's at the front of house. They already have 10k resistors at both left and right before all 8 channels mix together and are going through the opamps. So in that sense, you basically say that I just need to put a normal open switch between the left and right channels after those resistors? \$\endgroup\$
    – Hendriks3D
    Jan 27, 2019 at 13:10
  • \$\begingroup\$ Yes. You didn't show any of that in your original schematic -- just connectors. \$\endgroup\$
    – Dave Tweed
    Jan 27, 2019 at 13:22
  • \$\begingroup\$ Yeah, I meant to put this in the already working mixer. So I assumed you got that. I wasn't clear enough then. \$\endgroup\$
    – Hendriks3D
    Jan 28, 2019 at 15:33

Will it work - maybe. Your scheme relies on the left and right inputs being high-impedance if they are not you could get inter-modulation (which generally sounds terrible) when you switch to mono output.

I'd recommend a 1 kilo-ohm resistor in series with each input before the signals meet. You could put these on pin 16 an pin 13 of the mono-stereo switch. located there they would not participate in the signal path when switched to stereo.


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