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I am building a passive audio splitter that takes in two balanced mono signals (on TRS) from an audio interface and then it should be able to switch the routing of the signal using a DPDT switch.

I think the main function should work in my current schematic (feel free to correct) but I would need to incorporate two headphone outputs and volume knobs for them. I would also need a volume knob for the signal going through the switch.

enter image description here

The monitors are these ones.
Dont know about the other pair yet that is then switched between with this device.
The audio interface is this one.

Daniele Tampieri
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Keijo Kunnari
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  • Are the TRS input and outputs stereo signals or balanced? If you don't know, we can probably work it out based on the audio interface you are trying to connect to. – Graham Jun 03 '23 at 09:21
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    This is a lot to ask for a passive interface. As well as editing the question to let us know whether the TRS connections are unbalanced stereo or balanced mono please also add the signal levels and the impedances for each connection from their manuals/datasheets. As a starter the two input connections a and b are shorted together which is unlikely to end well. – Graham Nye Jun 03 '23 at 09:32
  • Thanks for the response. Could you elaborate what u mean by the signal levels and impedances? Of each component like the switch and such and TRS jacks? The TRS ins and outs are balanced mono. – Keijo Kunnari Jun 03 '23 at 10:37
  • Signal levels describe how big the voltage signals are, either in terms of peak voltage or an rms value. They might be described in volts, dBu, or dBV, which are just different ways of describing the magnitude of the output. Most datasheets or product manuals will describe the expected input and output levels. – Graham Jun 03 '23 at 10:52
  • Impedances describe the input and output resistances for each signal. This is importan because input and output resistances form potential dividers, which will reduce your signal level, particularly if not chosen properly. – Graham Jun 03 '23 at 10:53
  • I also think that it would be useful if you posted the equipment that you are trying to join up. The reason I mention this is because even though your signals are balanced, many interfaces can work unbalanced too with a TS cable, which will simplify your switching and volume control. – Graham Jun 03 '23 at 11:00
  • It's also worth noting that one of the core advantages of actually using differential signalling is that you don't need to have the exact same ground on all your equipment, greatly reducing chances for ground loops etc. Now, you decide to just bridge together all shieds – that can be very well OK, but it can also negate any positive effect you've gotten through using professional differential signalling. – Marcus Müller Jun 03 '23 at 11:27
  • Thanks. This is all a lot of new information for me. I added information about the main devices. Do I also need to consider the signal levels and the impedances of the parts used in my device like the TRS or TS jacks and the switch? The Apollo Twin accepts TS cables too and anything that makes this project simpler is most likely the best way to proceed. However, my friend who I am building this for, mentioned that he uses balanced mono at the moment and that the integrity of the signal is everything as he is quite professional. – Keijo Kunnari Jun 05 '23 at 12:49

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