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Tube Amp Buzz/Hiss

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Postby dl0571 » June 21st, 2008, 3:20 pm

Lately I've been getting a strange hissing buzzing sound from my Fender Blues Jr. It usually occurs when I'm playing on the lower strings and muddies up the sound quite a bit. It does not occur on the higher strings at all. The volume is pretty constant and is very noticable at bedroom levels. Not so much at higher volumes. I know it's not normal single coil hum because I've gotten the same buzz from a single coil and humbucker guitar. It does not occur when no note is played and as I said, usually only on the E and A strings, sometimes the D. It almost sounds like something is vibrating inside the amp.

Any ideas? I don't really have the money to have the local shop look at it as their tech prices are outrageous. I will get it looked at if I can come to a conclusion and am not comfortable DIYing it I'll take it in.
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Postby Ricochet » June 21st, 2008, 3:29 pm

How long have you been playing the amp? "Power tubes" (the EL84s in your amp) do wear out gradually, and it starts showing up as unwanted distortion. I'd expect more of it at higher volume, though. You may simply have something loose in your amp. Finding what to tighten can be challenging. Tubes can develop loose parts inside that vibrate and make noises. Called a microphonic tube. That's why you want to be extra careful not to drop, bump or jar your amp. Gently tap each tube with a pencil or something with the amp on and see if it reproduces the noise. Every tube will make some noise when you tap it, but you'll know if it's too much.
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Postby dl0571 » June 21st, 2008, 4:09 pm

Thanks Ric....I've only had the amp about 3 months and haven't had the time to put too many hours on them. I did check all the tubes before, took 'em out and popped 'em back in. No change.

If it helps, oddly enough the noise starts to dissipate as the amp heats up...

Hmm
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Postby Ricochet » June 21st, 2008, 4:59 pm

That's possible with a microphonic tube. Parts expand and change position as they heat. Might jam into their supports better. Try tapping the tubes. Can't hurt, and might turn up your problem. Finding something with a loose screw, etc. can be a tough hunt.
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Postby dl0571 » June 22nd, 2008, 1:55 pm

I think I found the problem on accident...

I usually have my amp set up in the living room but last night decided to move it to another room so as not to bother anyone else. As soon as I moved it the hiss went away. Turns out the socket I had it plugged into was improperly grounded.

Who would've thunk it?
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Postby Ricochet » June 22nd, 2008, 4:49 pm

That's not too uncommon. Glad you found the problem! Really ought to get the socket fixed.
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Postby jackss565 » June 23rd, 2008, 11:51 am

Glad you found the problem
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Postby tylert » June 17th, 2010, 8:15 pm

I have a Vox AV 100, and it is very temperamental. Sometimes I turn in on, and it sours and other times it is very buzzy. It drives me crazy because I have had the amp only two years, replaced the tubes already, and I still get the unwanted buzz. It is only slightly audible on the dirty channel but very evident on the clean channel.
I want to be confident that the amp will be in proper working condition for gigs. I would hate for this to happen when I'm trying to play live (which already happened once). Does anyone have any suggestions or possible solutions?
Thanks for any advice.
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Postby Ricochet » June 18th, 2010, 5:59 pm

Does it happen just in one place (suggesting a problem like the one above), or does it do the same when you take it somewhere else? Does using a different guitar and/or cable stop it?
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Postby thembones88 » June 29th, 2010, 5:23 pm

I have a similar problem:

I own a Marshall TSL100, and it sounds amazing (tone-wise, but there are other issues). It (like those posted before me) recently started a little hum/buzz, and like those before it is much more audible on the clean channel. I know it is not the outlet or any cable, because I've tried several outlets (even at different houses) and also the hum occurs even when there is no cable plugged in the input.

I am going to try tapping the tubes as was suggested, but I was wondering if there was anything else that could be wrong, like my input. Sometimes I notice I have to jiggle the cable plugged into the input to get sound, and I don't think every cable I own is just crapping out, I think it that might actually be my input (although none of my cables (planet waves) have been purchased in the last year/year and a half).

So I'll check the tubes, but if I don't discover anything could my input be the source of the problem with the hum???

Thanks
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Postby tomfoy » July 20th, 2010, 6:37 pm

Yeah man, sounds like either your jack is dirty, or the jack is coming disconnected from the PCB (if it's a board-mounted jack). You should replace the jack, or re-solder it to the board. This could definitely be causing your noise problems, and I'd check it first.
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