Bright Switch/Presence Oscillation on Express

[mumford]

I know I saw a thread on this somewhere, but I can't seem to find it.

My ceriatone express I built has very high pitched oscillation when the presence or bright switches are engaged. It completely goes away when I pull back the volume on my Hot Plate.

Any ideas what would fix this? Using a shielded wire from the presence knob to the 8 ohm output on the switch?

I remember in the other thread someone mentioned using long speaker cables and arranging them until it went away, but I'd prefer a solution rather than a cover-up.

[LeftyStrat]

Do you have shielding from the volume control to the second gain stage?

Even though the problem manifests itself with the bright switch or presence, the fix is usually found around v1 or v2.

[mumford]

Nope, I think my only shielded wire is the input. I'll try that. Thanks!

[markr14850]

Do you have a metal closing plate for the bottom of the chassis?

[mumford]

Not yet-- I haven't built a cabinet at all so far, so it's just sitting on top of a blanket on top of the speaker cab.

[markr14850]

If my speaker cables pass anywhere near the input end of the preamp without a closing plate, I get whistling...

https://tubeamparchive.com/viewtopic.php?t=3601