Ghost Sound LondonPower StandardPreamp

[Strelok]

Hi all!

We all know the song "Ghost Town" by "The Specials".
I have a problem with a ghost sound, but it is not coming from that town.

I built a Standard Preamp a long time ago, using circuit card and the
layout from the kit.
The gain channel has an extra sound that is a shrill and thin version of the gain channel.
It does not listen to any tone controls, neither on the clean nor on the
gain channel.

When I turn up the volume of the gain channel the sound remains the
same, same volume, but the normal sound comes up like it is supposed to.
So of course you cannot hear it anymore but it is still there.
I can tell because annoying buzzing is much worse in that preamp, so
those frequences get amplified more.
I have to turn op the volume (Pump Up the Volume) way too high to swamp
out the ghost.

A while ago I built another Standard Preamp and it has the same thing.

I don't have this issue with single channel preamps I have built, like
the Vintage and High Gain variations and the single channel "Y".
They are also on circuit card.

What can this be?

I remember somehting about electro-magnetic coupling, but I'm not sure
where I read that.
That would occur near tone controls or channel switches.

Or maybe I just dreamed that.


Kind regards,

Strelok