TL;dr - will a Stereo to Mono RCA adapter tolerate the same channel from two different sources (Left from Device 1, Left from Device 2)?

I have a bit of a weird use case that I am looking to create an elegant solution for. I think I have found it bit I don't know enough about the tech to understand if it will work or potentially damage equipment.

I have two sources of audio that output via L/R RCA into L/R RCA. I have one output device. I'm not looking to introduce a mixer, ideally

I want to play audio from both sources, through the one output.

Gear is as follows:

Source 1 (S1): Audio Interface

Source 2 (S2): DAC (audio from PC)

Receiver (R): Headphone Amp that outputs to headphones (duh).

For the purposes of my question, channels will be referred to as gear prefix followed by L/R channel, so Left out of the Interface would be S1.L and right channel input of the receiver would R.R

Here's what I am thinking:

      >--S to M cable- R.L\
S2.L/                      \
                             > Headphones 
S1.R\                      /
      >--S to M cable- R.R/

Will this even work? Will a stereo to mono accept a Left in Left AND Left in Right, and then play both in LEFT provided the mono end is connected to the Left input?

  • Hi MattB. Can I ask why you're doing this?
    – n00dles
    Commented Feb 7, 2022 at 14:45

1 Answer 1


It will possibly work without too much sound degradation. Simply try it, things will not break.

But, you run into a number of possible things , which in your exact case may be problems or not.

  • Ground loop hum: as the ground cables are interconnected you may get enough ground hum to be noticeable.
  • Interference from computer electronics: the computer is full of electronic interference from power supplies, CPU and GPU clock, USB connections and so on.
  • No control of relative volumes: well, you could probably do that other ways.
  • Degradation of sound quality: as two outputs will "compete" they will influence each other. The reason is that the outputs are low impedance while they expect to be connected to a high impedance input. Most probably some of the very low frequencys, possibly not hearable, may be decreased sligthly.

So, go ahead and try.

  • Yeah, I'd just try it tbh, but with everything turned down at first. And not with the headphones against your ears, just in case. Slowly turn things up - do it all gingerly and ready to unplug.
    – n00dles
    Commented Feb 7, 2022 at 14:38

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