Genz-Benz GBE250C

[jessenator]

IDK where this goes...

So maybe a year ago I made an impulse purchase on a used bass head to accompany my forlorn Ampeg cab. It played great in the store, but getting it home it had the hum, and I was either too stupid to take it back or it was sales final. Have a Furman conditioner power strip and it's still there. Come to find that my long unused Deluxe-inspired guitar Head also hums. Dinky solid state combo practice amp, no hum, and no other anomalies from other devices.

I'm not really in the mood to pitch the bass head unless it's a total goner. I want to repair or at least diagnose it, since it doesn't appear to be the house wiring. If anyone has the GBE 250C schematic, I'd be much obliged.

I have a feeling it's something on the power board, but having never worked on something like this, I have nothing but that hunch to go off of. Hell, I don't even know how to test it, schematic or not. I'm guessing I'd audio probe it to see where the noise gets into the signal...

Okay epiphany time while composing this message: it's definitely post preamp. I want to say I DI'd it into my DAW (balanced output is right out of the preamp IIRC) and there wasn't any noise, but I'll have to try again just to be sure.

I asked about it on a bass forum, and an actual former GB tech answered. His replies implied that my asking for the schematic would go nowhere, and that shipping to him would be cost prohibitive—oh and he hinted that the only thing worth keeping on that particular was the combo speaker assembly...  go figure. If diy fix is going to cost up to half of what I paid (overpaid more likely), or even up to the price of a decent replacement head, then maybe I do ditch it and go with something else. ¯\_(ツ)_/¯

[jimilee]

Wait, so you have two heads and they both hum?


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[jessenator]

Wait, so you have two heads and they both hum?

Gah, sorry, I knew writing that late has consequences  : P

Yes. I have a GBE250C hybrid bass head, and a hand-wired Fender Deluxe like head a friend built.

Both hum with or without the conditioner power strip.

Both of these are used with my ampeg 4x10, and from everything I've read, it's definitely not the cab, because cabs don't do that.

I also have a dinky line6 practice combo amp but its signal is totally clean, with or without the conditioner. That's why I want to say it's not my house's poor wiring, but I could be wrong.

It's just weird that both heads hum in the same way. I mean, the GB head has like half and half on yhe preamp stage only: so the amp is mostly FET.

I'll test out whether the preamp is clean by DI'ing into my DAW later tonight.

[jimilee]

Since it didn't hum in the store, I would go somewhere and plug it in there, or grab a ground lift adapter and see if that helps. They are Pennies on the dollar and can be picked up damn near anywhere.


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[lars]

Both hum with or without the conditioner power strip.

No surprise there. I've never had a situation where plugging into a fancy "conditioner" power strip fixes anything. But the manufacturers really like you to think they will help.

[BrianS]

Both hum with or without the conditioner power strip.

No surprise there. I've never had a situation where plugging into a fancy "conditioner" power strip fixes anything. But the manufacturers really like you to think they will help.

Ain't that the truth.  Either that or Furman strips just amplify it lol.

[jwin615]

Is it 60 cycle hum or more of a white noise?
Does the noise go away without a cable plugged into the input?
If so, bad cable is a possibility. Also RFI. Try turning light off in the area and unplugging other electronics. Cheap LEDs make a ton of RF noise.
Also, if it has an effects loop that has latching/half bornalled jacka, those can get funky and cause noise, volume dropouts and other issues.
Stick a short patch cable in the effects loop nd see if it changes.
Try another outlet elsewhere in the house as well, or get a ground lift  could have noise on your ground on that circuit but the Furman *should* have fixed that if it's an actual conditioner and not just a glorified surge protector with rack ears.

[jessenator]

Heyo

Yesterday was crazy, and I didn't check the DI again. It on its own has a ground lift, and it was engaged probably from the last time I tested it, but then again, my spawn might've had a time pushing buttons and twiddling dials on it since, so that's not a for sure thing.

I haven't bought a ground lift (at some point a neighbor and electrical engineer told me to get rid of them all, so I likely did), but I'll get on that hopefully today.

I have tried extension cording (orange, outside type) to most of the other circuits in the house to no change in results. If I had a smaller cab I'd just move it manually, but sucker's heavy  : P

Tried patching effects loop, no change

Hums, that wonderful 60Hz buzzy hum, instrument or not.

No other appliances on the main circuit I'm using, no lights on (or rather, no difference with lights on or off)

Looks like my strip is just a surge strip with "attenuation" for higher frequency RFI/EMI, so that explains that. Whatever, it was inexpensive what what it was and I needed one. Still, good to know it's not really doing anything.

Thing that puzzles me is that there's no hum from that dinky practice amp at all. Oh well.

[jessenator]

Alright, had a smidge of time and Ace was close. Got the lift/cheater plug and there's no difference :/  except for a pop when it was going straight into the wall  : P

Welp, sounds like there may be issues with the transformer, I take it?

[jimilee]

Yep, it's new isn't it?take it back.


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[jimilee]

Yep, it's new isn't it?take it back.


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[jwin615]

Alright, had a smidge of time and Ace was close. Got the lift/cheater plug and there's no difference :/  except for a pop when it was going straight into the wall  : P

Welp, sounds like there may be issues with the transformer, I take it?

How old is the house? Any chance that room is missing it's ground? Or the outlet is inverted?
You could kill the breaker to it and ohm out the neutral(bigger slot, left side)to ground.
Could also add a big honking ferrite bead to your next tayda order

[jessenator]

How old is the house? Any chance that room is missing it's ground? Or the outlet is inverted?
You could kill the breaker to it and ohm out the neutral(bigger slot, left side)to ground.
Could also add a big honking ferrite bead to your next tayda order

1990, so no post-construction ground retrofitting. Can't imagine a singular outlet is missing a ground, or anything else on the circuit, tbh.

Not sure if the outlet is inverted. What sort of resistance am I looking for?

I always thought ferrite beads were more for data/digital signal cleansing, but I'll look into it.

[jwin615]

How old is the house? Any chance that room is missing it's ground? Or the outlet is inverted?
You could kill the breaker to it and ohm out the neutral(bigger slot, left side)to ground.
Could also add a big honking ferrite bead to your next tayda order

1990, so no post-construction ground retrofitting. Can't imagine a singular outlet is missing a ground, or anything else on the circuit, tbh.

Not sure if the outlet is inverted. What sort of resistance am I looking for?

I always thought ferrite beads were more for data/digital signal cleansing, but I'll look into it.

Resistance should be in the ohms rating, shooting from the hip, 2-12 depending on wire gauge and length.
As far as the ground, never underestimate the hunger or a mouse or the haphazardness of a hungover electrician or framing apprentice.
Ferrites filter emi and rfi, critical for digital, but can be helpful in audio. If you're dealing with 60 cycle, no use trying. If it was hiss, maybe.

[jessenator]

I want to have strong words or perhaps smack a fool, because whoever labeled my breaker box labeled everything not a major appliance as "bedroom" and the "master bedroom" as not the master bedroom, till I was prepared to shut them all off, except we had something critical going on.

it's a bloody mess... eventually I'll figure out which h*cking breaker goes to the basement.