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Hi, I have been looking for a forum to post questions about working commercial amps and this was suggested. I won't be able to check back till this afternoon but I'll throw this out and see if anyone has any ideas. I have a Marshall 6100 that is noisy on the crunch and lead channels. The noise comes in on the 1st stage for these channels, V2A. Since it's a commercial amp, there are no lead dress issues because the design works. Everything seems to be ok componentwise and I went through the ground solder connecs with no luck. Now I'm thinking of pulling the socket cause there might be something going on under it where I can't see. But it will be a bitch to get out and I have to reuse it. The noise sounds like hiss with a little crackling, and looks like a mess on the scope. Seems to track ok with my scope set to line triggering so it might be 60 cycle harmonics. Anyhow, I am stumped. Any suggestions? Thanks in advance!
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Probably a resistor gone noisy.Education is what you're left with after you have forgotten what you have learned. -
Hi Enzo, I will replace the components in that circuit before I pull the socket. Are you talking the plate and cathode resistors? The input seems to be very touchy, I can press on the board and make the signal jump. But can't find any obviously bad solder joints. Re-flowed everything no change.
Here's the link to the schematic http://www.drtube.com/schematics/mar...6100-61-04.pdf
If I pull V2 the noise is gone and I can see it with the scope on the output.Comment
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Still need help with this Marshall 6100 noise issue
Well, this is the worst amp I have worked on yet. I replaced cathode, plate, and grid resistors, even the grid stop. Still makes noise that goes away when V2 is pulled. I pulled the socket and it looked ok, cleaned up and reinstalled and the thing still makes noise. I removed the cathode bypass cap and no change. I am out of ideas. The noise is 60 cycle related, it will track with my scope set on line triggering. Like a distorted sine wave with a lot of hash all over it. Anyone? This amp is killing me
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