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Alright this is driving me insane. I'll get some pics shortly. Basically once I turn up my OD past 75% I get a super high pitched squealing even when the guitar has the volume off. I do not have the footswitch mod.

1. Changed tubes to known working tubes (from a Sovtek Mig50H with no problems), still get it
2. Moving the grounded wire going from the OD pot to pin 2 affects the amount of squeal but won't eliminate it. reduced by volume significantly when it is not running along the bright volume pot..
3. The mid control effects when it comes on. turning mids way down lets me turn the OD up another %2-3. Same-ish with treble.
4. Gets worse when master is turned up - although I'm in an apartment so I can't say how bad it gets

searching online its hard to tell what the root causes are. I tried to follow layouts/pictures - the zaphod phil pictures have the footswitch though so that makes it harder

Try moving the shielded wires around, they are very sensitive.

Without seeing a pic I'd say your lead dress (wire route) is the cause of the oscillation.

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Is there anything in particular that might make it worse for some positions? ie: near an input jack = feedback loop, or near some other signal route in particular that I would want to stay away from?

all the pushing around has made my wiring look EVEN messier

Try the coax lead above the board.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

rewired with coax/shielded cables above the board - virtually no change - moving around the coax above the board doesn't really change anything

I notice if I push on the ground bus with my chopstick, the squeal is reduced/eliminated but then if I push the OD knob up another 2-5% its back, so it maybe just gets me a little further and that's it - but maybe there's a bad connection there somewhere, would that do it?

It's a really really high pitched squeal.

Try rerouting those shielded wires around the terminal strip with the 2 470K resistors. Just move them around with a chopstick and see if you can find a place where the noise stops.

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it does get better when I bring them close to/flush with the strip that those resistors are on, but still not eliminated. Anyone have pictures of how there's is routed, maybe I can start there and then try to eliminate other problems that could be impacting?

I spent 15-20 mins just moving them around with no real change, at any point it maybe improves or degenerates 2-5% but I can't get much higher than 75% of the knob without it squealing

maybe I'll just go through and resolder all ground connections..

viewtopic.php?f=14&t=2959


That purple wire that goes from the tag strip to the OD switch I'd make it as short and direct as possible. Avoid having it close to any other wires.

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rewired that purple wire, now it's hissing too - great. I think I might rewire that whole section because I think I'm making it messy.

Weirdly, if I turn up the master the squeal goes away from like 2-4, and then when the master is passed 5 the squeal comes back but it cycles off and off.

I had the same issue. I think I ended up using shielded wire for that purple one. Also, it still squealed a bit after that, but once I had it in the cab with shielding on the bottom of the chassis it stopped squealing altogether. That area with the purple is crazy sensitive to lead dress.

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SG + Brit tube head = Nirvana

still have the squealing issue after replacing it with shielded wire - but I'm going to put a panel on the bottom of the chassis (self made cab) and see if that helps. It DOES seem to be better after putting shielded in that location. might try rerouting again now

Almost a year later haha.. my own laziness of not completing right away, and geting frustrated (not to mention it still sounds incredible so long as you don't crank the OD)

I've virtually eliminated the squealing unless everything, OD and bright channel is cranked. I think if I spent more time on it I could get it out all together

1. cleaned up some of my lead terminations
2. shortened some leads (this is probably the biggest issue)
3. Ran most leads under the board.

My entire build now when I look back at it looks messy and I should've just taken the time and re-cut leads to be as short as possible. I'm bad at estimating so I often had them just a little bit longer so I didn't to keep recutting but in the future I'll just go till I get it as clean as possible.

Thanks for the update. Glad you got it worked out. Lead dress is critical and always worth spending time on.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps