Hi, I'm new to the forum, but I hope someone can help.
I have had this problem on a few solid state amps in the past, the current one is a Marshall "Reverb 12" (Model 5205)
This is with a standard humbucker equipped guitar going direct into the amp. Guitar and cables verified 100% good. This problem happens at any volume or gain setting.
Plug guitar in, play for a few seconds gently, everything is fine. However, if I hit a big chord or start playing aggressively, the amp has a fraction of a second at normal volume, then the volume drastically reduces when I smack it, and limps along with hardly any gain. Unplug, plug in again, its fine until I hit it hard, then it happens again. Something is cutting out under stress, regardless of whether the amp has been turned on 10 seconds or 1 hour. I have plugged into the headphone output and the same thing happens, so it is presumably a preamp issue. I have checked and cleaned the input jack surfaces and checked for dry joints, had the PCB out and gone over that really carefully for obvious problems, there were burn marks round the zener diodes on the +/- rails (had this before on small combos), so I changed them for higher wattage ones to be sure, but the problem still persists. Caps look good, no bulging or obvious deterioration. This is probably something stupid, but I have limited experience with solid state stuff, and would really appreciate some pointers as to what might be causing this, as I have had quite a few solid state amps do this to me over the years. This Marshall is an incredible little bedroom amp, and I'd really like to fix this myself if I can. Is there a common cause for this sort of behavior?
Many thanks, and sorry for the long post!
Pete
I have had this problem on a few solid state amps in the past, the current one is a Marshall "Reverb 12" (Model 5205)
This is with a standard humbucker equipped guitar going direct into the amp. Guitar and cables verified 100% good. This problem happens at any volume or gain setting.
Plug guitar in, play for a few seconds gently, everything is fine. However, if I hit a big chord or start playing aggressively, the amp has a fraction of a second at normal volume, then the volume drastically reduces when I smack it, and limps along with hardly any gain. Unplug, plug in again, its fine until I hit it hard, then it happens again. Something is cutting out under stress, regardless of whether the amp has been turned on 10 seconds or 1 hour. I have plugged into the headphone output and the same thing happens, so it is presumably a preamp issue. I have checked and cleaned the input jack surfaces and checked for dry joints, had the PCB out and gone over that really carefully for obvious problems, there were burn marks round the zener diodes on the +/- rails (had this before on small combos), so I changed them for higher wattage ones to be sure, but the problem still persists. Caps look good, no bulging or obvious deterioration. This is probably something stupid, but I have limited experience with solid state stuff, and would really appreciate some pointers as to what might be causing this, as I have had quite a few solid state amps do this to me over the years. This Marshall is an incredible little bedroom amp, and I'd really like to fix this myself if I can. Is there a common cause for this sort of behavior?
Many thanks, and sorry for the long post!
Pete