Can a Bad Transistor...

[Paul Marossy]

cause hum? I've exhausted every other possibility for my humming wah...  the only thing I can think of is that one of original transistors may be faulty.

[hank reynolds 3rd]

i think transistors can get @#$%ed...i've had a few ...dont know what i did to screw them tho

sam

[Paul Perry (Frostwave)]

What kind of hum is it?
If it sounds like 'mains' hum, it almost certainly isn't the transistor.

[Paul Marossy]

It does sound like mains hum, but I can't figure out how it's getting into the circuit. Where should I look? I've tried adding a 1M pulldown resistor on the input, still got hum. I tried adding a 100ohm resistor in series with the power supply and a 100uF cap across the power supply, still got hum, but slightly less. I tried powering it up on the same power supply as the rest of my pedals, still got hum. It hums with a battery in it, too. I thought maybe I had a ground loop, tried messing with the shielding, still got hum. I just don't get it, why?!?

Here is how my pedal board is setup:
http://home.att.net/~u2p0j0m4/PedalBrdDiagram.pdf

I am a little stumped on this one....  :x

[Mike Burgundy]

transistors can be damaged (hooking them up wrong way round will make them noisy for ever) but it doen't sound like mains hum, more like hiss, pink noise or spluttering.
You're sure it's the wah? Make absolutely sure the cables to and from the wah are good, and the internal wiring is ok, without ground loops or unecessary lifts. Is there something like fluorescent lighting, computer monitors, routers close by? Is the supply filter cap in the wah ok? Etc.
Borrow a similar wah and see what that does. See if your wah does the same hum-thing in a different location, etc.
hih

[Paul Marossy]

Well, it didn't have a supply filter cap originally. The first thing I tried is adding one of those (100uF).

I made sure all lighting with dimmer controls were off, computer was off, too. Nothing seems to make a difference. Perhaps it will bahave differently if I move it somewhere else... I'll try that, too. It maybe could be my doorbell transformer which is about 8 feet away from where I keep my amp.  :shock:

I'll give that a try and see what happens. Thanks for the ideas.

[Paul Perry (Frostwave)]

Does it hum when a battery is hooked up?
that will tell if it is a power supply problem.

[Paul Marossy]

Yep, it hums wth a battery, too.
I am running 7 other things on my board with a Boss power supply. Maybe a bigger cap across the power supply might help?

[hodad]

Does it hum when the Boss power supply is not plugged in (or in another room?)  My guitars pick up wallwart hum pretty easily--don't know if the wah might too.

[Paul Marossy]

Yep, it will hum even when taken out of the pedalboard and when it is all by itself - guitar-->wah-->amp. Just for for, I stuck a 2000uF cap across the power supply, still no reduction in hum.  :cry:

[Rob Strand]

What you have so far is, it hums with,
- batteries
- power supply
- when used in the pedal configuration and alone

So basically if you connect it like,

Guitar-> cord -> Wha -> cord -> amp

where the wha is powered by batteries *and* you have no other connections like wall-wart leads hanging out of it,   you still get hum, yes?

and so there is no possible connection you can make which has no hum, yes?

If so then I can only suspect a wiring problem in the wha.  Some wha's have kind of weird ground wiring and if one of the jack connections is corroded, or there is corrosion between where the jack metal bites into the paint etc of the metal case then it could very well give you hum.   I'd expect the hum to have a bit of buzz as well but it something to persue.  Perhaps unbolt and rebolt the input and output jacks, and clean them up a but with a cutex or something.

[Rob Strand]

Something else, try lifting it 1 meter or so off the floor and try orientating it in different directions left, right upside down and see if it has any effect.  The  wha inductor could be picking up field from mains wiring under the floor.

[Paul Marossy]

Well, I know that there is no electrical wiring under the floor, it's a concrete slab on grade.
One of the first things I tried was cleaning the input and output jacks with a .30 caliber gunbore cleaning wire brush dipped with some solvent because I had noticed that the brass contacts looked nearly black! But that didn't help anything at all.
I also did try moving it around here and there, three feet in any one direction, but still get a hum.
I guess I'll have to look at how the grounding is done and see if I come up with anything there. Maybe I have a bad solder joint in there somewhere, although I don't see anything that looks suspect...

[RDV]

Paul:

Have you tried the old 100uF cap and 100 ohm resistor trick for filtering?

HTH

RDV

[Paul Marossy]

Yep, I tried that, too. I tried a 220uF cap, too. Still get hum.  :evil:

What's funny about this whole thing, is that my new manufacture GCB-95 circuit has absolutely no hum at all. It's on the same place on my pedal board, connected exactly the same way as when I was doing my testing with the humming &#%&%^ circuit. But, when I try the old vintage ciruit in its place, I get major hum.

I just don't get it...

[RDV]

I'm guessing again, but I'm fearing you have a broken wire in your inductor. It happens to all my pick-ups on all my guitars in the bridge position because of my foul disgusting acidic sweat.

Regard-a-mundo

RDV

[Paul Marossy]

Now that would make sense. I'll look into that. Thank you!