Susan_B_Good

Susan_B_Good, 2 years ago

I’m puzzled - you describe wanting to add a headphone jack (eg an output jack socket into which headphones can be plugged) - yet you seem to actually want a socket that provides auxiliary input.

However, if you are indeed trying to add external input and are disconnecting the inputs to an amplifier - you might want to tie those disconnected inputs to ground.

Susan_B_Good, 2 years ago

It’s usually a good idea to look at what’s normally connected, when breaking a circuit, and replicate that. Which I seem to remember is a 10k resistor with a parallel capacitor (being too lazy to go back and look again). You could try the same combination, in place of the added input cable, on the lines that you plan to use and see if it whines. If not, add the cable(s) and try again. That may stop it happening on all channels.

There are two muting methods - open circuit the input (via a switch or a gate) - in which case there will probably still be some signal transfer through capacitive coupling - especially if the amp side of the open circuit is high gain. Or short the signal path to ground - and that short will have some impedance and thus the signal is only attenuated and not removed all together.

Turning the amp gain to far higher than it ever would be in practice is hardly a fair test. There aren’t many amps that will be noise free under those conditions - and, in this case, there will be a signal to amplify, albeit highly attenuated.

It’s good to be cautious - cascade failure can be waiting to bite. Never direct connect unless unavoidable - add a series capacitor, if you can. Yes, not usually a good idea to provide a dc path unless essential and, even then, current limit it if possible.

Susan_B_Good, 2 years ago

Thanks for the suggestion - I think that there are inline adapters to a different plug, but finding a different coaxial plug that will handle that current could prove challenging.