Fender Fuzz-Wah issues

[Unlikekurt]

Hello all,

I have a first issue Fender Fuzz-Wah that is exhibiting some issues; I hope perhaps someone has some insight or advice.

I replaced C1, C11 and C12 with new electrolytics to start.

First, I was getting much much less than unity output with either the Fuzz or the Wah engaged.
I first looked at the output of the fuzz.  I looked at the voltage divider between R8 (470K) and R9 (100K) and changed R8 to 100K.  On the scope this gave me much much closer to unity output when the fuzz is engaged.

Now I'm still having issues with the wah circuit.  I have a big decrease in signal output when the wah is engaged and frankly speaking it's hard to see whether or not it is working properly. 
The hFE on the three PNP germaniums was a little on the low side (sub 100) so I tried replacing all with transistors in the gain range of 300.  No change.

Looking at the schematic the voltage on the PNP transistors from left to right are:
E: -.055
B: -.181
C: -2.525

E: -.786
B: -.940
C: -2.45

E: -.210
B: -.339
C: -2.92

The battery voltage is: 8.17

Any help would be greatly appreciated.
Thanks!

[thermionix]

Do you have an in-focus version of the schematic?

[Unlikekurt]

Unfortunately not.  I would utterly love having an easily readable schematic with sharp edges and crisp lines to share.

[pinkjimiphoton]

haha, thats the best copy of this schematic i've actually ever seen.

the fuzz etc on this is a little below unity on all the ones i had of the original series. since it wasn't truebypass nobody really noticed the volume difference back then.

the cat to talk to with this one is probably Gus Smalley, he helped me clone this years ago but i don't remember what we did. i do remember i encountered a phasing problem with it... that may have been the later unit. wish i could help more.

i would start with an audio probe on this one... when the signal drops, that will likely be the culprit.

[Unlikekurt]

Was able to get back on this for a little bit.
The schematic is awful, but yes, the best version I have been able to track down as well :/

I traced my way through and have some findings; the fuzz side of things is fine and has decent tone as well.
On the wah side, surprise - surprise, the problem arises at the inductor.  Signal looks "ok" at the start of the coil (indicated on schematic as "blk start") and at the "finish" (indicated on schematic as "Finish green" the signal is pretty much vanished).

I took the indcutor out of the circuit entirely and jumpered from the "start" to the "finish" and not surprisingly, now that circuit acts as a rather large boost.  More reason to suspect the coil itself.

Took some measurements of the inductor:
Start to Finish =48.6 Ohms / .47H
Start to CT = 41.5 Ohms / .375H
CT to Finish = 7.2 Ohms / 8mH

So the "finish" is pretty much shorted to the center tap and per the schematic the center tap is grounded.
I do not have any other coils around to take readings off of, are these suspect of a faulty coil?

Thank you for any further assistance.

James

[pinkjimiphoton]

i dunno man, that coil's dc resistance looks like it may be ok. and the tap is probably right. is this the one with the rotary knobs on the top of the treadle, or the huge chrome behemoth where ya twist your foot for volume/fuzz and wah is "normal"?

i have one of the chrome ones if its that model.

i would suspect a bad cap or resistor, but i gotta see the schematic to look at it. i mean.. not much in an inductor to go bad, really, if it shows continuity thru i would think its good... but other folks here are a lot smarter than me.
any numbers on the inductor we can try and match up?

[antonis]

I'm also very close to Jim suspection for bad cap or resistor..

Wah resonator is actually a RLC 2 pole filter (high-pass by its own but effectively low-pass due to its NFB loop placement..)

It creates a band-pass filter in conjunction with input cap HPF..

IF resonator Q and frequency are "deviated" due bad to cap/resistor, band-pass filter upper and lower frequencies might overlap resulting in signal level decrease..

[Unlikekurt]

Thank you for the feedback.
The pedal is indeed one of the giant chromed out metal version and a nice selection of small diameter rope to turn the potentiometers.
There are bypass switches for the fuzz as well as the wah.  They are located to the outside of the pedal, one on each side.
The volume function is horizontal movement of the pedal and this is non-bypassed.
I will go through the wah circuit and take a look at component values versus their markings.  In the process I may go ahead and draw a clean schematic as well
In the mean time i'm going to attach the image I have the best I can here.
As you can see such a low resistance (7 Ohms) between the CT and the Finish of the inductor would seem to serve to short the signal straight to ground, nearly entirely.

[pinkjimiphoton]

7 ohms is plenty in this case, as the inductor kinda needs to be grounded.
i really doubt thats your problem.
i'd start by checking all them shitty tropical fish caps. replace all/any electros. but odds are ya got bad r/c netwrork somewhere.
i will try and dig mine out today if i get a chance.

[Unlikekurt]

I have gone through the board and tested each component.  Didn't find anything unexpected; but thought I've gone this far so why not replace as well.
Summation: no parts on the board showed any fault but now all have been replaced.

With that being said, things are working a bit better now than they had been.  My suspicion is that there must have been a bum solder joint somewhere that I didn't see in my visual inspection that was remedied when soldering the new components into place.

I marked up the schematic as I went with the values and will do a little JPG editing to upload for you guys. 

Now the only issue i'm experiencing is on the sweep of the wah there is a spot where there is some crackling.  My suspicion is that the pot is at fault (as everything else has been replaced).  However, these appear to be sealed pots so I'm not sure i'd be able to clean it.  And taking one out and replacing it would be a bugger to get all the ropes in JUST the right place with JUST the right number of loops and the collet in JUST the right place with the shaft turned to JUST the right spot of resistance...

[thermionix]

I've never had any luck cleaning the sealed pots.  Yeah I can get the back off but the typical cleaners seem to just make them noisier.  My theory is that is has something to do with the wiper, which has a black chunk of carbon-based something, instead of just bare metal contacts like you see in most pots.  But I don't know, could be the resistive track, or both.

[pinkjimiphoton]

check the last cap before and after the wah. sounds like some dc may be getting passed.
the wah isn't very great on these, but the fuzz is fairly good.
suspect another solder joint for the crackle.  you CAN clean these pots, but its a pain in the ass.
if you do opt to open it, pay attention to how it goes together, where the stop fits etc or you'll have even MORE shenagans to deal with.
damaged track? no prob. #2 pencil is your friend. use your pencil eraser on the carbon track, then lightly go over it with the pencil. put a little of that conductive grease stuff in there <or soak it down with some caig or something similar> and CAREFULLY put it back together. it will work for a while, the pencil lead will fill in any damaged parts of the track. if you're lucky it will work. if not... guess what the drill will be wear rubber or cloth gloves, and be quick and as clean as you can. try not to  breathe on it too much.
i DO have a "how to restring fender wahs" pdf somewhere or other i can upload to ya if you end up needing it.
but i am betting its a crackly solder joint somewhere. keep us posted bro!

[Unlikekurt]

Thanks!
And, I can REALLY use that how to restring PDF at this point and would be very very grateful.
When this came into my hands the movement was very rough for the wah.  I watched a few videos and it looks like it should be able to stay in the toe down or toe up position on its own.  However, I can only seem to figure out how to make this "spring back" to toe-down (and a few ways to string it so it does that as well...)
All components are new, so I don't think i'm leaking DC. 
I'm going to try to get some contact cleaner in down the shaft (forunately the volume pot had a nice opening to get cleaner in on the rear).  I started looking for a replacement and surprisingly I had several reverse log 50K potentiometers BUT none of them had a long enough shaft to mate with the collet.

[pinkjimiphoton]

soon as i can get to my other computer. pm me an email addie to send it to
i MAY have it on my facebook... gimme a sec

god i hate facebook. let me poke around i know i uploaded it there, but... they suck, they suck, and not only that?

you guessed it.

[pinkjimiphoton]

sent bro, hope it helps...

hey, where's a good place to share files these days, anyways? someone else may need it one day, too