I am a bit stumped with this one. Unfortunately there are a few variables involved, but I will do my best to ask an answerable question....
I just built a DIY synthesizer. It functions absolutely fine. This is the pcb design:
plugged into a small guitar amplifier, it functions normally, and the on/off switch functions to disconnect power from the synthesizer.
However, when I plug it into my mixing desk, any audio lead attached to it disables the on/off power switch and the synth is always powered up. The synth continues to work properly, I just cannot disconnect the power with on/off.
I had the idea that this is occurring because it is somehow providing an alternate ground (because I don't believe it can be supplying a voltage, especially not one that would not have destroyed the synthesizer) when the ground is disconnected by the on/off switch.
With that in mind, I put a Ground Lift "hum remover" in between the synth and mixing desk. Sure enough, this solves the issue and the on/off switch operates again.
The mixing desk itself is connected to an audio interface as both input and output, plus several other synthesizers, and a microphone.
is there something obvious causing this that I am missing? I am a bit stumped as to what is happening (I would assume an error in the assembly of the synth, but the issue does not exist with other inputs!)