I don't know if this is the correct forum to ask this, but I have a problem with my audio set up.
The setup goes as follows: PC -> external audio card (via usb from pc) -> stereo equalizer mixer (via headphone output from audio card) -> speakers (via rca audio outputs from equalizer).
I want to add my guitar amp as a speaker and the only available output in the equalizerbis the one for headphones (the equalizer allows to play the sound from rca output and headphones at the same time).
But my problem is that when I connect the amp, the speakers start a high frequency humming sound (which is also heard from the amp).
To be clear, the setup works with no problems when the amp isn't connected.
I tried to put actual headphones in the equlaizer and there was no humming.
When the humming is heard and I move the cursor around, the humming sounds a bit louder.
The amp that I am trying to connect uses a 6.5mm jack
The humming is heard whether the amp is on or off.