[sdiy] Humming noise in JH reverb circuit

[ganesha]

Hello,

I have a small problem. I made Jürgen Haibles synthi reverb http://www.jhaible.de/tonline_stuff/hjsc_vcr.gif
Everything works, but I can hear a loud humming noise in the circuit.

I only hear it when I turn the mix knob to wet signal. When it is set to dry signal (no reverb) there is no humming anymore and I hear the original audiosignal perfect.

If I disconnect the reverbtank from the PCB the humming gets louder as soon as I disconnect the wire coming from the output of the reverbtank. That connector on the pcb even starts acting as an antenna.
If I move my hand closer to the connector without touching it, the humming gets louder.

I've shielded all the audio wires, including the ones going to and from the reverbtank.

I've never debugged a circuit for hum before. Is there a way how I can find the problem by using my oscilloscope for example? Any other tips on what I can do to find the problem?


Thanks!
Best regards,
Kris