Re: Practice amp.. Marshall Valvestate 8040 ..Volume Problem
- From: Jim <askme@xxxxxxxxxxxxxxxxx>
- Date: Wed, 05 Dec 2007 17:43:40 -0800
how would i go about doing that, the fx loop suggestion? you think if i opened it up and clean the posts out with some electronics cleaner it would fix the problem? Any chance it could be a bad pre amp? The amp works, but when you play longer than 5-10 minutes all the volume cuts out.. when you turn it on an off it make a crackling sound; turning it on and off doesn't fix the problem.. if you turn it off, and leave it be for 10 minutes it works fine when turned on, but the volume eventually burns out the same way it did the first time.. i just bought it today, so i still have a chance to return it, but if it's an easy fix.. than i'd keep the amp.
I'm a hobbyist that has built, modified and repaired tube and SS amps and effects. I am not a pro and don't claim to be an expert. Other than that...
My crystal ball tells me that it's probably a broken solder joint. When there's enough heat from the power transformer and output devices, the board expands and you get an open circuit. Either that, or there could be some sort of overheat protection tied to the heat sink for the output devices (probably a chip in that amp, but I don't know). If that's the case, something is wrong, causing it to overheat. I'll assume that you meant cleaning the POTS, not the posts. That ain't gonna fix it.
My crystal ball is not always right. But why did you buy a broken amp? What did you pay? For perspective, I think I paid $20 for a 8020 with scratchy pots. Gave it to my nephew. Kind of a mistake, because now I get to clean the pots on a regular basis. ...and direct replacement pots are oddballs that aren't that cheap!
If you have electronics skills, or at least a good soldering iron and the ability to solder, you might try resoldering all of the pots and jacks to start with. But this design is NOT a good one. Look forward to more problems like this, and dirty pot hassles. IIRC, you gotta pull all the knobs, take off all the hex nuts, pull the board... HASSLE!
My advice: BRING IT BACK.
"jh" <jh-audiop_NOSPAM@xxxxxxxxxxx> wrote in message news:fj2s9m$oj5$01$1@xxxxxxxxxxxxxxxxxxxx
if you fell i love with the 8040 (*), check it out again and patch the FX loop with a short cable. If the symptoms are gone then, it´s a corroded or dirty switch contact of the return jack..
You could either use it till the end of our days with the patched loop, or have it fixed for about 40-50 $.
(*) although I can´t understand why
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