Unexplainable amp hum

[sublimerules9604]

Ive noticed that even with my guitar unplugged and my amp (blues jr) turned all the way down, I still get a fairly good sized amout of hum. It seems to do this regardless of the tubes, because I have JJ's in mine and a bandmate has the stock ones in his and they both hum like crazy. I read on Billm's blues jr mod page that adding a strip of sheet metal will make a noticible difference, are there any other opinions on this?

He also mentioned that changing the output transformer would make a huge difference not only in hum, but in tone, well thats how i took it... Again what do you think?

Thanks

 

[drpietrzak]

Re: Unexplainable amp hum

BillM is the man when it come to the Blues Jr. to me. I would suspect there are other mods but his page covers most of the main ones. Also, as I recall, the hum repair you are discussing was for the greenboard version I think. It was to correct a reverb circuit issue. I believe the creamboard (newer - after to 2000) have a different circuit and are brighter.

Try the amp without any reverb and it should quiet down if that was the issue. Also, what do you have running on the same electircal circuit? Or does it do it on all circuits? Are you hitting the amp with a pedal?

 

[sublimerules9604]

Re: Unexplainable amp hum

You can have every knob turned off and no volume at all and absolutely nothing plugged into the amp, and still get it. I just tried the reverb thing, and turning it all the way up or all the way down didnt make a difference. As for the circuit, it has the same amount of hum running into a power conditioner or straight into the wall. Someone also mentioned a while ago that switching the wires around on the input (I think) would help, but the guy I know who did it is gone for a month.

Thanks

 

[Empty Pockets]

Re: Unexplainable amp hum

Well if your amp is on and your guitar is unplugged and all the knobs are at 0, aren't you just about to turn the amp off anyway?

 

[Fresh_Start]

Re: Unexplainable amp hum

Unfortunately the Blues Jr. is not noise-free. I've read Bill Machrone's stuff, and he's got two or three "solutions" to the noise problems. One is a piece of sheet metal shielding the OT from the PT. Another does have to do with moving the reverb on green board (older) versions that was corrected by Fender for the cream board (newer) versions. He also blames the OT, and there's a lot of discussion about alternative OT's on the Fender Discussion Page in the "Blues Jr. Mafia" thread and others.

Someone at Allen Amps told me there was a design problem with the grounding method and replacing the transformers wouldn't help with the noise. Given that I was asking in terms of "would your transformers fix this problem", I tend to believe them.

I still like my Blues Jr. despite its imperfections.

Chip

 

[WhoFan]

Re: Unexplainable amp hum

good to know these amps are noisey... i hate noisey amps... my JCM 800 is extremely noisey... lots of hum when the standby is on and no cord in the jack... Bad mod done to mine... But i have often thought about buying a Blues Jr to mess with...

 

[Fresh_Start]

Re: Unexplainable amp hum

good to know these amps are noisey... i hate noisey amps... my JCM 800 is extremely noisey... lots of hum when the standby is on and no cord in the jack... Bad mod done to mine... But i have often thought about buying a Blues Jr to mess with...

Yeah, I have the caps for a tonestack mod and came across a neat way to turn the un-used half of V2 into a cathode follower in front of the tonestack. Got fix the reverb insertion point. Backing off the extra-hot bias and adding some bias adjustment would be good. A replacement OT. Then a slightly bigger wood cab (instead of whatever crap this is)... Wait, maybe I should just build a new amp!

Chip

 

[drpietrzak]

Re: Unexplainable amp hum

I think the Blues Jr is the single most used amp I have. It is the jack of all trades. It is not a quiet amp, but it is not really any noisier than most of the amps I have here, and have vntage to higher end. The noise shoud not be a serious issue realtive to any other lower cost production amp. If it is there is something not right.