induction loop amplifiers..

a well known cause of grief to electric guitar players, usually in the form of feedback.

Does your Laney amp have a spring reverb unit in it, and do you use it?
Are the leads connecting everything up screened?

Did you try my suggestion of keys-->mixer-->stagebox, and using the control room outs of you local monitor?

Reading you latest message:
I'm wondering if the intermediate box is a passive DI box working backwards.. that is taking the balanced out of the main desk (aux 1 going from what you said), and converting to a unbalanced high impedance source for the loop amp.
Unplugging the leads to the main PA amps will make the system go quiet!
Touching them onto any metal work of the stagebox (odd the main returns being on jacks, and not XLRs) and the signal re-appearing tells me that someone before you doesn't know how to wire a 3 pin XLR from the main mixers main outs.
Pin 1 Screen ------> Jack screen
Pin 2 Signal hot --> Jack tip
Pin 3 Signal cold -> Jack ring

I think Pin's 1 and 2 have been switched.

If you can provide some info of the main mixer it would be very helpful, as some mixers made in the US of A (Peavey, Mackie) have been know to swap 2 and 3, but that would only effect the phase of the signal , as pin 1 is still screen.

Does the venue have an in house engineer?
If so I suggest you get together, possibly re-wire the lot!




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