Marshall jcm900 squeal at power off

[hollisdevillo]

I have a jcm 900 dual reverb 100w that works fine. everything seems good, BUT, when i turn it off it gives a little squeal. like a chirrup. or a lightsaber sound. what would that be? capacitor? if so, which one? how can i check it? how can i find out what part of the amp is causing the problem?

thanks for the help!

[R ski]

I have incorporated integrated circuitry into my home brew Marshall like tube amps, when the power is shut down, I experienced some similar sounds. Looking at the schematics at http://www.schematicheaven.com/index_HTML.htm I noticed a lot of IC's used as buffer stages in that model.

Probably one of the chips are the cause while the DC rail diminishes when the power is shut down. If you are experienced at poking with electronics the VCC rail capacitors should be checked for good connection or if one broke off from what ever. If opening up electrical components and circuit cards with electronics is not your thing, I wouldn't worry to much about messing with it, as long as your happy with the performance when your playing