yes, yet ANOTHER wah thread

[eleanor296]

sorry guys...
I really feel bad about all this wah talk, but I can't seem to find the info I need.

Here's my problem:
http://www.yourfilehost.com/media.php?cat=audio&file=wahnoise.wav

As you can hear, the noise increases as I move the wah to the toe down position.
Any idea why this could be?  Is this what a "scratchy" pot sounds like?  If not, I'll get you guys some voltages.  I had to remove it to clean everything, and put it back in without any "fine tuning", so maybe it's just adjusted wrong?
The wah is from the 80's, the circuit is basically the "newer" Dunlop one (in respect to parts values), but it doesn't have the buffer or protection diode.
Here's some pics:
http://s20.photobucket.com/albums/b206/eleanor296/wah/


Thanks!
~Andy



The previous owner tried to install a DC jack and LED, but didn't in the end for some reason... all of the wires on the pot were just clipped off, so that's why I had to solder 2 wires together on the middle lug.  I'll clean up the wiring once I fix it, true-bypass it, and install an output buffer.


Thanks!
~Andy

[R.G.]

Before you get too far in mondo mods, replace the transistors with 2N5088 or 2N5089 and replace all of the electrolytic caps with same-value but new caps.

It is likely that the input transistor has gone noisy. Toe-down position passes more treble hiss.

[eleanor296]

  the 5117's... worthless?   
ok, will do!

[eleanor296]

wow... old thread.
So I changed the transistors... same issue.  Sound is the same too.  Plus, as I said, the hiss in the toe down position 
so today I got it back out and changed the pot... still nothing.
Is something wrong with my inductor?
I changed the electrolytic cap too, by the way.


Thanks
Andy

[R.G.]

Here's the poop - toe down position passes through any noise that exists in the circuit, toe-up filters it out. The noise is there always, but the filter makes it inaudible. Given that it was not the transistors and not the caps, then it is likely one or more of the resistors; wires and copper traces don't produce much hiss. 

I would replace the 68K input resistor with a fresh carbon film; if that didn't help, I'd change the 1.5K going to the first transistor's base. It's almost got to be an input resistor. Not absolutely, but almost.

[eleanor296]

Thanks R.G.,
I'll try that.
Though right now it won't work again with the old pot... grrrr....
I'll report back.

[eleanor296]

replaced the 68k with a 20k and 47k in series, and the 1.5k with a 2.2k and 5k in parallel (both metal film).
Still... same issue.  Man.. this sucks.  Audio probe doesn't really bring anything else up either.

Thanks for the help though, R.G., it's really appreciated.  Learned a lot from your articles. 

~Andy

[R.G.]

If you've changed the wah pot, changed the transistors, and changed the electrolytic caps, you're left with the following:

- Bad solder joint (just go remelt them all)
- Noisy resistor other than the one I mentioned.
- Leaky non-electro cap.

Unless there is a bad solder joint or almost broken wire inside it, the inductor is not likely to be the source of hiss.

Frankly, I'd get a new batch of resistors for every one and just start replacing them one by one. There aren't enough to spend more debugging time on.

[eleanor296]

ok.. will do!
OZr try at least, hehe

[Dai H.]

there appears to be a bare (uninsulated) splice going to the pot. Looks awfully close (touching?) to the enclosure.

[eleanor296]

there appears to be a bare (uninsulated) splice going to the pot. Looks awfully close (touching?) to the enclosure.

Hey Dai H,
that's been insulated.
I had to somehow "lengthen" the original wires, so I attached a little bit of new wire to each, so they'd reach the pot.  It's all insulated now though.

thanks
Andy

[Dai H.]

I'd try R.G.'s suggestion of remelting solder joints (or at least check over all the newer ones that were made when and after the problem appeared) since I think a bad joint can help to make it sound like you have a scratchy pot. I think I've had that problem before.

[eleanor296]

I'd try R.G.'s suggestion of remelting solder joints (or at least check over all the newer ones that were made when and after the problem appeared) since I think a bad joint can help to make it sound like you have a scratchy pot. I think I've had that problem before.

Yeah, will do.
I've bought the wah use and the pot was disconnected... some other stuff too.  It's been like this since I hooked everything up again.

~Andy

[petemoore]

  When in doubt, start with a schematic.
  Try the usual quick-over [well, you've been over this thing], then do the 'dogmatic' debug, test that every value is correct, and that every connection of the circuit is made and that there are no 'extra' connections.
  Since you got it like that, I would guess either something on the board is shorting or somehow became open, or even more likely the offboard wiring has an issue.

[roknjohn]

Just out of curiousity, are you using a power plug or a battery? You stated that the previous owner tried to install a DC jack, but didn't say if you were trying to use it or not. I've also had power supplies cause all kinds of strange noises. If you haven't already, try a fresh battery.

Roknjohn

[eleanor296]

yeah,
I'm using the DC jack...
should I try some power supply filtering?
my power comes from a dunlop dc brick.

~Andy

[eleanor296]

  so I put in a battery clip and tried it with battery... hum gone.  Yay.
But... new home.  Nooooo.
Before I put in the battery clip, I replaced the new resistors with the old ones (since they were fine and I had to use 2 in series or parallel as replacement) and reflowed all switch and jack connections.  Now I got what sounds like a ground loop with the pedal off.  With the pedal on, I only got very faint sound.  This pedal really hates me.
I'll get to it with the audio probe tomorrow.

~Any

[eleanor296]

still nothing new.
Checking everything out again, reflowed every solder joint.  The thing with the power was false alarm.  Actually, it didn't work at all for a while haha.
Now it's working again.  But nothing new.  Man...
I'll post some more pics.
Audio probe doesn't really give me anything, believe it or not.