Wah'ing around - need help

[aron]

I'm trying to work on a wah pedal and I can't figure out why it doesn't wah as good as another one which has identical values and in fact has the same numbers on the board and stamped in metal. It's a Crybaby wah and for some reason, it just doesn't sound as intense as the other "identical" wah.

Of course I've read R.G.'s article and referencing this pic:



I've put a 1K trimmer on RE1. Now turning it closer to zero will make the sound fatter and more distorted as well as move the wah frequency lower. It does make the wah seem "more intense" but it mainly adds more distortion once you get past a certain point.

I put a 100K trimmer on Rq and it does seem to affect the "wah" depth, but not nearly enough. It goes from not much to acceptable. There is no hint of "feedback" in this wah.

I socketed Cf and it does work indeed. By changing the capacitor value I can move the sweep up or down. Different types of capacitors seem to change the sound in different ways.

The elusive missing component is the "depth" of the wah. Like the resonance depth of an analog synthesizer filter. This would seem to be Rq, but Rq doesn't seem to affect the sound nearly enough.

Any ideas how to increase the "intensity" of this wah? They both have TDK inductors - the "good" wah has a round one, the "problem" one has a TDK but it's square. Both are brown.

I have no problem changing the inductor, but will that increase the intensity of the wah?

BTW: Yes, I did change Cbp to a brand new 4.7uF electro. Yes, I did play with the pot sweep mechanically.

Thanks,

Aron

[RobB]

If this was my problem, I'd be swapping components between the good wah and the problem wah.  
The inductors could have different characteristics in terms of value in mH and the DC resistance.  Try swapping those first.

[aron]

Good suggestion. The good wah is mine. The bad one is a trashed one of my friends. The only thing is I might not want to take mine apart since it sounds so good  

[Lonestarjohnny]

I would replace the electro's first, you may have an old cap that's causing a problem.
Johnny

[Fret Wire]

Sound like your basically down to transistors or the inductor. You could try some MPSA18's, 5089's, or 3904's to see if the originals have gone bad.

[petemoore]

I count 8 non resistor parts, I doubt any of the resistors failed.
 If everything is wired correctly, which I assume it must be, and al the caps are 'alive', I would be questioningly eyeing the *inductor.
 Probably has good MPSA18's, but these aren't hard to swap out for to test.
 I would do the 8 parts tests, starting with the caps or inductor, transistors, Checking any 'open' resistances of the board, say Q1 is out, you can definitely and easily check that Re1 IS what it says it is, all the way from ground to the tranny socket. replacing one by one with testing after each replacement the caps and tranny might tell you which one was the culprit, or that none of them were.
 other resistances can be taken also, but you have to look at the alternate current path that may be there, and regard/disregard or compute the readings....or just pull one end off the board and see exact how much the R value of that resistor is.
 Does one of the wahs boost more than the other?
 Does it have reverse polarity protection?
 I put my chips on the inductor as the main differentiator.

[R.G.]

Try changing Rfb. That changes how much of the resonant signal gets mixed back into the straight signal.

The resonance of the classic inductor wah is limited by the inductor's internal Q (that is, how "pure" an inductor it is versus how much resistance is there as well) and Rq, and to a lesser extent the ESR of the 4.7uF cap, the output impedance of the follower transistor, etc. That's why a big resistance at the 4.7uF cap position makes it into a volume pedal - the Q of the resonant circuit is dropped all the way to zip. It's also why you want a low-resistance inductor.

But try Rfb first.

[aron]

OK, I tried replacing Rfb with a 10K trimmer. Hmmmm..... It makes a difference but not that much. I also tried replacing Q1 to a 2N5089, and it didn't make much of a difference.

The wah works, just that it doesn't sound very special at all.

[Arno van der Heijden]

What transistors does the 'good one' have?
Maybe try some lower gain ones, like BC10x?

[aron]

Maybe, but R.G.'s article implies that higher gain will "stabilize' the circuit. If I can fix this pedal, I can probably fix any Crybaby after this.

[Fret Wire]

Did you take voltage readings off Q1 & Q2? Or readings elsewhere, especially at the harness plug? Bad soldering connection on the jacks, switches, pot, and main wiring plug? Even the factories screw up  once and a while.

[Aharon]

I have built two very similar ones,one is throaty the other is less pronounced.
The only diference I can see is the inductor,one is a stack of dimes and the other is generic.
I also used a 5117 transistors and Doug's fet input.
I swapped pots but no dif,even using a 50K was good.
Aharon

[aron]

I'm going to take transistor readings tonight.

Thanks!

Aron

[Hal]

I think it _might_ be the inductor.  Honestly, I have little wah experiance myself, but everything i read says that most of the "tone" of the wah comes from the inductor.  try to make everything about the bad one identical to the good one, except for the inductor, then swap them, and see what happens :-D

[aron]

I guess I'm going to try and get some Dunlop Fasel re-issues. I can't decide whether to get the yellow or red?

I looked back in the archives and most people got the Red - which is the "cleaner" tone version.

Any thoughts on this??

[Fret Wire]

Red is the clean, and Yellow is the classic sound. I've only tried the Yellow, and I like it. If you have to get  them from the mainland, Antique Electronics has the best price.

[aron]

Hmmm ok, they are biased very close to each other:

Q1 - mine

B .552
C 3.451
E 4.3mv

Q1 - his

B .561
C 3.582
E 16.8mv

Q2 - mine

B 2.963
C 7.37
E 2.533

Q2 - his

B 2.973
C 7.39
E 2.552

so they are close. BTW, those silver caps... what type are they? They have a red stripe on one end. Does the stripe mean anything? They are not electros right?

Thanks,

Aron

[Lonestarjohnny]

I agree with Fretwire, I've tried the red and yellow, the red for me was to bright for the kind of rig's i've been hammering on lately, My peavey classic, a Traynor Guitar Mate, and a JTM 45, with the yellow i get a better break on my E.Q. to where if I want it with more treble it's easy to adjust, anyway i like the yellow too !
and CD distribution has a great price on them.      
Johnny

[Fret Wire]

The emitter on his Q1 is a little off from your's.
Do the caps look like these? They're metal axial tants.

[Fret Wire]

JD, do you have a link for CD distribution? I gotta check em' out.