Marshall amp problem with sound going up and down

[kerrmit13]

Hi All,
i sent an amp recently to Davis for repair. Problem is that the sound goes up and down after a while. The tech mentions that there is a sudden drop in the voltage and a fuse has been changed the some circuits have been cleaned. The amp was brought home and the problem resurfaced and it was sent back to Davis. It was tested on the spot and the problem with the going up and down surfaced during testing. The amp was left with the tech for a month and I was told that there is no problem with the amp. The tech did not change any parts and the amp was allowed to run for long periods to check for the problem. Verdict is that there is no problem with the amp. I took it back and realized after playing for about 30 minutes, the problem will resurface. Any experienced tech here who is able to advise? Thanks!

 

[hidetox]

Hi there. It may be helpful if you could let us know the model of the amp.

If it happens to be a YJM or AFD, chances are that this volume fluctuation is due to the EPA set at low volume combined with a non consistent power supply. I had experienced this with the afd and sent to Davis for check up. Tech found nothing suspicious and got it back with nothing changed. So far so good for me.

 

[kerrmit13]

Thanks Hidetox for the reply! I am unable to understand some terms. What's YJM,AFd and EPA? Mine is a 30 watt solid state amp.

 

[hidetox]

hi. AFD and YJM are the different models from Marshall. you mentioned that yours is a 30 Watt solid state. hmmm... I guess other amp experts can chip in on this one. If not, you can send in you amp to Scott from Sound alchemy... all e best!

 

[Vax]

When exactly does the problem surface? If you wobble the volume or gain knobs, does it make the amp stutter in volume? How's the condition of the speaker cable connection with the speaker?

I ask because one of my solid state amps happens to have a similar problem, and I found that when I give the gain knob a nudge up/down, the amp crackles and it momentarily resumes its normal volume. However, I decided not to do anything about it since the "lower volume" is still useable.

 

[Nicholasim]

i have the same problem with my marshall mini stack. Think its a voltage problem. Could be our house power supply cause lesser volts to pass through sometimes thus the fluctuation of volume

 

[ShredAddict]

the lower end marshalls use terrible parts. have the tech to check the capacitors. IMO they are just not built to last.

 

[puremilk]

is your amp problem being fixed?maybe i can take a look for you.