JCM 800 - Combo - Channel Bleed

[Scatterwound]

Hi All,

I own a JCM 800 4210 model. It is plagued by the infamous channel bleeding. I did some research on the net that this was a Marshall design flaw.

Does anyone know of a fix? Is there some modification to the schematic that would fix this? Or am I doomed?

Thanks!

[glassman]

Re: JCM 800 - Combo - Channel Bleed

9 times out of 10, changing C47 (50uF @ 450v electrolytic) for a new one of the same value will do the trick. Sometimes you have to add additional capacitance to the 50 (up to 100uF) to get the bleed to stop.

The design flaw in these amps is there are too many gain stages on one power supply node(there are 7...usually 4 is really pushing it and invites cross-talk); you can split the power supply and add another node but that's kinda difficult unless you know what you are doing. Either way, I'd leave it to a tech unless you are comfortable pulling the board out of the amp and know what you're doing around high voltage...too much heat and you WILL pull a trace from the board.

In rare cases, you may have to replace the 16 pin IC.

[Scatterwound]

Re: JCM 800 - Combo - Channel Bleed

Thanks glassman....I do have a tech I can get this done....I will pass this info on to him...Thanks a bunch!