Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 12AX7 on February 22, 2012, 12:29:21 am
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My 2204 (similar, not exact) home brew has a buzz. It doesn't hum like a PSU issue, but a buzz like a SC pickup or a bad ground. Problem is, i have checked and rechecked the grounds and nothing in the ground scheme has changed since this started. I've chopsticked it to death, tho i think thats more for hum issues if i'm not mistaken. What other things would you suggest i check? I can upload a sound file if need be, tho i'd need someone to point me to a free upload site. But really all you need to know is what the buzz from a SC pickup sounds like and you already know.
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Which knobs change the buzz loudness or tone?
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it's coming from the preamp from what i can tell. Turn the gain or master off and it's gone so it would seem to be before the gain pot, but that leaves little i haven't yet checked. Also, turning the guitar pot all the way down makes it go away. I've tried 3 HB guitars and all the same buzz.
Any pot affects it to one degree or another except the bass pot which i take it is because the buzz is well above it's freq range.
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> turning the guitar pot all the way down makes it go away
Then between guitar pot and first grid. Cable?
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No, i've tried 3 including one short 2' patch cable. i also thought maybe the jack lost isolation and maybe getting a loop, but nope. Gonna try a new jack and 1m resistor next.Maybe all new....cable from jack to grid and grid stopper too. That'll leave nothing left to be suspect between the jack and grid.
I did find something very very odd tho, and i don't know whether this could be connected to the noise or what on earth could cause it. If i touch the signal path with my finger (yes, i know, but i'm old anyways and wouldn't lose too much time :icon_biggrin:) anywhere after the 1st coupler all the way to the next grid, it of course as expected makes a loud buzz. If i do the same after the second coupler to the 3rd stage grid, ZERO noise ! As tho i'm not even touching it. This is with gain and master up and guitar plugged in. What could cause that? I replaced the plate R and coupler even tho i can't see how those could cause this when the amp is fully functional and sounds great. WTF?
EDIT: did it, replaced all things from jack to tube pin and no diff.
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uhhhhh....well, i guess i'm done with this issue. It's too bizarre. I unplugged the guitar and left the cable in the amp and the buzz stops. Now remember, i tried 3 guitars and 3 cords. Somehow the guitars, all of which are the same i've been using long before this started, are i guess allowing the noise in the amp, but they must be connected. Maybe this is a clue, but i can't figure it out so i think i will have to live with this one.
EDIT: Wow, never woulda thought this...it was the BELTON socket, V1. Beltons are great, but apparently when you resolder them one too many times they can give up. I was staring at the amp about to give up and throwe it back in the cabinet when it hit me thats the only thing i hadn't swapped out at some point. Realizing i had a old chassis i'd cannibalized with relatively new beltons i tried it and success. Whew....load off my mind !