JCM 800 Hum

[SeanMichael]

Ok all, I think I have a problem. When my JCM 800 (2204) is on, its produces this loud hum. It feels louder than the natural hum of a tube amp should be. What can I try to try fixing such a problem?

This is a clip of the sound. The MV is at 12 o'clock. This recording sounds a bit buzzier than it actually sounds, mind you. And this is with nothing plugged into the amp.

[SC]https://soundcloud.com/seantremel/jcm-800-hum[/SC]

 

[StratoMarshall]

Without some troubleshooting it's hard to say, but it sounds like it may be filter caps. Does it play ok?

 

[SeanMichael]

Yea, it plays fine.

The hum increases and decreases in intensity consistent with how high the master volume is set.

It has gotten progressively worse since I bought it. It hadn't been used much before I bought it.

 

[StratoMarshall]

Yeah, that probably is the filter caps. This is something you want to look into immediately before it goes "POOF"! What year was it made?

 

[SeanMichael]

1987

 

[Alabama Thunderpussy]

I wouldn't go doom and gloom about filter caps yet. Did this hum arise suddenly or has the amp done this since you got it? Backstory is important. If this is a recent development, it could just as easily be a preamp tube issue, or dirty input jack.

Does the hum occur with nothing plugged into the input?

 

[GtT]

I've read and been told by techs that 2203s and 2204s are inherently noisy and can get bad radio interference. I've heard humming 2204s myself. Is this true?

 

[john l]

Im with Bama, sounds like a tubes on its way out to me.

 

[Micky]

Put in your spare set of tubes and see if it still does it...

 

[damienbeale]

Can't diagnose ANYTHING until you are sure that the tubes are good. Always keep a spare set of known good tubes.

 

[SeanMichael]

The tubes are brand spankin new (about a month old). 2 Mullard EL34s in the power, and 4 Sovtek 12AX7WBs in the preamp section. The problem was there even before the tubes were replaced.

Like I said, it has been a gradual development ever since I got the amp.

Yes, the hum in the clip is without anything plugged into the front of the amp.

 

[Alabama Thunderpussy]

The tubes are brand spankin new (about a month old). 2 Mullard EL34s in the power, and 4 Sovtek 12AX7WBs in the preamp section. The problem was there even before the tubes were replaced.

Like I said, it has been a gradual development ever since I got the amp.

Yes, the hum in the clip is without anything plugged into the front of the amp.

Okay in this case the next place I would look is the input jack, then the tube sockets. A dirty input jack or tube socket can cause issues with noise and hum. Clean them. If you still have hum, then you can begin looking at Electrolytics.

If the caps are original, chances are good that this issue is related to them. In truth, you should just replace them anyway on principle. But it helps to rule out simpler causes before jumping into larger solutions just as a matter of good practice.

 

[supershifter2]

I decided to do some research on JCM800 hummmmmmmmm ! I have 3 2205. 1-1988 , 2-1989. They have all new tubes and ps caps. One of the 1989's has a low level hum. The other 1989 and 1988 are quiet ! Swapped tubes , ps caps from one and still hums. Looked up hum problem with the 800 series and found lots of hum problems with these amps on the web. Hmmmm ! I donno but they sure sound good when playing a strat through them. This poor guy never got the hmm out > http://music-electronics-forum.com/t38597/

 

[neikeel]

Kind of a necro post as the OP has not been here since 2014 and did not bother to check back in with a solution which is very rude if people have bothered to think about a problem and post replies.

 

[MarshallDog]

I had a similar hum on my 1980 JMP. Nothing I did fixed it so I took it to my Amp Tech and he spent some time with it. It wasnt the filter caps vecause they were new. He ened up doing a bunch of maintenance to it including some new resistors, various caps, changed it to a star ground, changed some shielded wires, twisted a few wires and diffierent preamp tubes and this amp is perfect now. This amp did not like Mullard 12ax7s, ery noisy in v1. Matter of fact, I have since gotten rid of the Mullard preamp tubes in all my amps and they are much guieter, ive been using EH 12ax7s.

Just saying you could waste alot of time and money chasing this with no luck...

 

[Kris Ford]

I had a similar hum on my 1980 JMP. Nothing I did fixed it so I took it to my Amp Tech and he spent some time with it. It wasnt the filter caps vecause they were new. He ened up doing a bunch of maintenance to it including some new resistors, various caps, changed it to a star ground, changed some shielded wires, twisted a few wires and diffierent preamp tubes and this amp is perfect now. This amp did not like Mullard 12ax7s, ery noisy in v1. Matter of fact, I have since gotten rid of the Mullard preamp tubes in all my amps and they are much guieter, ive been using EH 12ax7s.

Just saying you could waste alot of time and money chasing this with no luck...

Which is why I want my '74 JMP to have a fine tooth comb ran through it..HOPING it's the caps for me, as they are the original Dalys, but I want everything checked.

 

[ampmadscientist]

Ok all, I think I have a problem. When my JCM 800 (2204) is on, its produces this loud hum. It feels louder than the natural hum of a tube amp should be. What can I try to try fixing such a problem?

This is a clip of the sound. The MV is at 12 o'clock. This recording sounds a bit buzzier than it actually sounds, mind you. And this is with nothing plugged into the amp.

[SC]

Pull out the first 2 preamp tubes, V1,V2. Leave the PI installed.
Now crank the master to 10, is the HUM still there?
Follow along and make the tests one by one.

 

[ampmadscientist]

Which is why I want my '74 JMP to have a fine tooth comb ran through it..HOPING it's the caps for me, as they are the original Dalys, but I want everything checked.

Unless somebody has a high voltage cap analyzer tester, it's pretty useless compared to just swapping out w/ new ones... low voltage tests mean very little.

 

[neikeel]

http://www.ebay.com/itm/Semcor-RC11...828426?hash=item41b74813ca:g:DA8AAOSw44BYIMF8

One of these

 

[supershifter2]

I had a similar hum on my 1980 JMP. Nothing I did fixed it so I took it to my Amp Tech and he spent some time with it. It wasnt the filter caps vecause they were new. He ened up doing a bunch of maintenance to it including some new resistors, various caps, changed it to a star ground, changed some shielded wires, twisted a few wires and diffierent preamp tubes and this amp is perfect now. This amp did not like Mullard 12ax7s, ery noisy in v1. Matter of fact, I have since gotten rid of the Mullard preamp tubes in all my amps and they are much guieter, ive been using EH 12ax7s.

Just saying you could waste alot of time and money chasing this with no luck...

All 5 of the 12AX7 are EH. I tried swapping them around and that didnt take the hum away.