Nasty high pitches tone

[Shevans]

Whatever you do,don't ask Russ Andrews,or he will sell you something for ten grand that all his customers swear by,,or swear at...

However shorting out the inputs (which you can do with a bit of wire) may help and Russ has just the product...

http://www.russandrews.com/shorties-57359990000/

[Dr Bunsen Honeydew]

"Nasty high pitched tone" - Do you have a wife or girl friend

[guydarryl]

stand the boxes on their sides? Daft idea - but if orientation of an aerial affects sensitivity to signal, would orientation of components, to the waves from interference, in amp matter?
I hasten to add that I am a chemist!

[jammy395]

Have you tried a good old thump.

[Ed345]

I tried the tin foil with an acrylic case. Maybe I'll try agin with it inside a big cardboard box...

I've tried the amps in different locations and positions but it doesn't seem to make much difference - which made me think it might be something on the mains input.

I've just desoldered the input to the volume control and moved all the input cables away from the boards, but the tone is still there. Is it strange that the volume control still controls the tone even though there is no input connected to it?

No Jammy I haven't resorted to hitting it yet. At first I thought that it had been damaged in the shipping process, but I've got 3 NVA amps here and they're all doing the same thing.

[Ed345]

I've tried the amp in a big cardboard box wrapped in tinfoil. Didn't seem to make much difference (apart from I need to buy new tin foil).

[jammy395]

Time to re-locate.

[Ed345]

Time to re-locate.

That is the plan, but staying here for a few more months at least.

I'm going to try some ferrite rings on th mains cable to see if that makes any difference.

Don't really want to go buying expensive mains regenerators etc as it's only a temporary location.

[terrybooth]

The tone stays on when the power is turned off. Fades away after about 10 seconds.

This indicates that the interference is not mains borne - the interference remains with no mains power. (Try pulling the plug rathen than turning the switch if you want to convince yourself.) I have no idea whether ferrites will work at all, but I'd try them on the signal cables. https://en.wikipedia.org/wiki/Choke_(electronics)