Marshall Amp Hum

[ido1957]

I usually have my amp master and pre at 10:00 (1/3 Volume). I don't play really loud. Last night I heard a slight hum coming out of the speakers. I turned the master up full and it's a pretty loud hum. This is even without any guitar plugged in. Is this normal to have noise/hum coming out of your amp with nothing plugged in? Or even with something plugged in (besides that pickup noise). I just fully re-tubed/re-biased the sucker about two months ago. I would have thought no signal = no hum....

 

[TelePaul]

Well all electronic devices have a noise floor of some sort....but it sounds like it's louder than expected; loud enough for you to notice it now but not in the past.

 

[ido1957]

I just finished playing a gig Saturday then carted the thing back home Sunday. I didn't notice it at the gig but then again, it was a little noisy venue. My basement is dead quiet so it would be more noticeable. I'm wondering if it bounced around too much in the back of the truck. Maybe I'm just being paranoid...

Any Marshal JCM900 4100 model owners out there care to open up their master volume to see if they too get a hum?

 

[espskully]

Is this when it's in hi gain mode? Or at any setting?

 

[ido1957]

Is this when it's in hi gain mode? Or at any setting?

Any setting. I tried a bunch of things...speaker cable, unplugging line out, high/low gain, speaker output, speaker input, stereo/mono, impedence.

 

[espskully]

Any setting. I tried a bunch of things...speaker cable, unplugging line out, high/low gain, speaker output, speaker input, stereo/mono, impedence.

Might be a problem then. Time for the amp Doc? You have anyone good up in 'chuck?

L&M here is always backed the hell up. My Mesa has a reverb connection problem. I have been putting off bringing it in because it'll be gone forever.

 

[ido1957]

Might be a problem then. Time for the amp Doc? You have anyone good up in 'chuck?

L&M here is always backed the hell up. My Mesa has a reverb connection problem. I have been putting off bringing it in because it'll be gone forever.

L&M did the tube replacement a few months ago. Guess that's where I'd take mine for repairs too.

 

[ggunn]

I usually have my amp master and pre at 10:00 (1/3 Volume). I don't play really loud. Last night I heard a slight hum coming out of the speakers. I turned the master up full and it's a pretty loud hum. This is even without any guitar plugged in. Is this normal to have noise/hum coming out of your amp with nothing plugged in? Or even with something plugged in (besides that pickup noise). I just fully re-tubed/re-biased the sucker about two months ago. I would have thought no signal = no hum....

All tube amps, in my experience, hum a little. As the filter caps on the power supply go bad, the hum increases. If the hum is bad enough that it hinders your playing, then it may be time for a cap job. If not, ignore it until it does.

 

[dementedchord]

All tube amps, in my experience, hum a little. As the filter caps on the power supply go bad, the hum increases. If the hum is bad enough that it hinders your playing, then it may be time for a cap job. If not, ignore it until it does.

+1... i'ld be checking those filters for sure... but at the same time if it seemed to change after moving it i'ld also check the tube sockets... try to tighten them.... with the power of and drained... take a small screw driver (i use a dental pick) and close up any that look too open...

 

[ido1957]

mjhamil came over to check out my other amp and I asked him what he thought (he's an electronics journeyman). He said it was 60 cycle hum. What do you do to reduce 60 cycle hum? I turned off lights and stuff and plugged it into different plugs and it still hums. Will a power conditioner help? Like a Furman?

 

[JCH]

bad tube?

When you had it re-tubed you could have got a bad one. I does happen fairly often with all the cheap Chinese, and Russian tubes being re-branded. Unless the amp is pretty old it's unlikely, but not impossible that you could have leaky filter capacitors. That would cause a 120 cycle hum. Take it back, and tell them that you think it's a bad tube. That way you can have it checked out for free.