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DIY Stompboxes => Building your own stompbox => Topic started by: aron on August 22, 2004, 05:28:11 AM

Title: Wah'ing around - need help
Post by: aron on August 22, 2004, 05:28:11 AM
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:

(http://geofex.com/Article_Folders/wahpedl/wah8.gif)

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
Title: Wah'ing around - need help
Post by: RobB on August 22, 2004, 06:41:20 AM
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.
Title: Wah'ing around - need help
Post by: aron on August 22, 2004, 06:54:29 AM
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  :)
Title: Wah'ing around - need help
Post by: Lonestarjohnny on August 22, 2004, 10:42:47 AM
I would replace the electro's first, you may have an old cap that's causing a problem.
Johnny
Title: Wah'ing around - need help
Post by: Fret Wire on August 22, 2004, 11:12:15 AM
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.
Title: .
Post by: petemoore on August 22, 2004, 11:13:16 AM
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.
Title: Wah'ing around - need help
Post by: R.G. on August 22, 2004, 11:25:00 AM
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.
Title: Wah'ing around - need help
Post by: aron on August 23, 2004, 03:33:41 AM
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.
Title: Wah'ing around - need help
Post by: Arno van der Heijden on August 23, 2004, 07:34:40 AM
What transistors does the 'good one' have?
Maybe try some lower gain ones, like BC10x?
Title: Wah'ing around - need help
Post by: aron on August 23, 2004, 03:44:19 PM
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.
Title: Wah'ing around - need help
Post by: Fret Wire on August 23, 2004, 03:55:53 PM
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.
Title: Wah'ing around - need help
Post by: Aharon on August 23, 2004, 04:26:17 PM
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
Title: Wah'ing around - need help
Post by: aron on August 23, 2004, 05:00:01 PM
I'm going to take transistor readings tonight.

Thanks!

Aron
Title: Wah'ing around - need help
Post by: Hal on August 23, 2004, 05:20:20 PM
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
Title: Wah'ing around - need help
Post by: aron on August 23, 2004, 06:48:24 PM
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??
Title: Wah'ing around - need help
Post by: Fret Wire on August 23, 2004, 07:38:56 PM
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.
Title: Wah'ing around - need help
Post by: aron on August 24, 2004, 02:32:06 AM
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
Title: Wah'ing around - need help
Post by: Lonestarjohnny on August 24, 2004, 02:47:56 AM
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.   :D  :D  :D
Johnny
Title: Wah'ing around - need help
Post by: Fret Wire on August 24, 2004, 02:48:51 AM
The emitter on his Q1 is a little off from your's.
Do the caps look like these? They're metal axial tants.
(http://i10.ebayimg.com/02/i/02/37/0f/21_1.JPG)
Title: Wah'ing around - need help
Post by: Fret Wire on August 24, 2004, 02:52:37 AM
JD, do you have a link for CD distribution? I gotta check em' out.
Title: Wah'ing around - need help
Post by: aron on August 24, 2004, 02:56:11 AM
No, they are weird plastic looking types.

I'm going to get a number of the yellow in and make them available. Yes, they will be less than Antique Electronics.

As for the emitter, that's based on the 1K trim pot, I can make his or mine identical.
Title: Wah'ing around - need help
Post by: Fret Wire on August 24, 2004, 03:11:15 AM
Quote from: aronI'm going to get a number of the yellow in and make them available. Yes, they will be less than Antique Electronics.

Aron, that would be great! And you can beat their already low prices? Any chance of the Fulltone pot also?

Santa Claus ain't got nothing on you! :)

It's really starting to look like the inductor, huh? Sounds like you've eliminated every thing else. The caps sound like some sort of tant. In any regard, the stripe must mean they are polarized.
Title: Wah'ing around - need help
Post by: aron on August 24, 2004, 03:26:33 AM
Yes there is the Fulltone pot. Fulltone's parts don't usually discount that much though. I will try.

Here's the type of cap:

(http://www.diystompboxes.com/pedals/photos/wahcap.jpg)
Title: Wah'ing around - need help
Post by: Fret Wire on August 24, 2004, 03:30:33 AM
It's got radial leads. Hmm..? With an older pedal like this, did you check the trace side of the board?
Title: Wah'ing around - need help
Post by: aron on August 24, 2004, 03:50:11 AM
Yes I did. It looks ok. The only reason I ask about the stripe is that particular cap is oriented backwards from all the rest. I don't think it's an electrolytic though.
Title: Wah'ing around - need help
Post by: Fret Wire on August 24, 2004, 03:57:33 AM
My upside down isn't so good...what's it say on the cap. Does it have a value code? You don't have a capacitance meter do you? That's one sure way to find out it it's polarized. Maybe tomorrow morning, someone will recognize what it is.
Title: Wah'ing around - need help
Post by: aron on August 24, 2004, 04:03:36 AM
Yes I do have a capacitance meter and I don't remember anything different about one of the caps I removed.

Hehehe you can see the value in my pic. It's a .22uF cap. I suppose it _could_ be tantalum... I guess.... I doubt it though.
Title: Wah'ing around - need help
Post by: aron on August 24, 2004, 05:04:43 AM
You know all these years, I've loved the sound of wahs, but I've never been picky - you know. I use it and I've always had Crybabys and the've always worked for me. I just step on em and use em.

I've always kind of ignored the wah circuit because after reading R.G.'s article, it looked so easy and well, after modding my wah it WAS easy!

Only after working with these "bad" wahs do I realize this simple circuit is sneaky!  :shock:
Title: Wah'ing around - need help
Post by: Geoffrey Teese on August 24, 2004, 05:26:24 AM
Hi Everybody,

Those funky looking silver caps were made by ITW.  Simple mylar wrap and fill.  Non-polarized.  They look funky but there is nothing wrong with them.  Unless they are way out of tolerance, there is no need wasting your precious time changing them out.  Folks who get a buck saying the caps are inherently bad and should be changed are just selling snake oil.

I can't offer any specifics about the wah in question as I rely on my ears to tell me what is "wrong" with any wah that comes in for service.  I don't have a stock set of fixes - it all depends on what is going on with the individual piece.

If you'd like specific help, please email me directly so we can sort of carry on a conversation and work through a host of possibilities.  I don't check in on sites as a general rule so I might miss a question you'd ask here.

Peace, Love, and Wah,
Geoffrey
www.realmccoycustom.com
Title: Wah'ing around - need help
Post by: aron on August 24, 2004, 05:33:48 AM
Yes, the caps that I measured were within spec. I'm thinking it's the inductor at this point. I will find out soon.

My "stack of dimes" wah I have - has a wicked sound. If I can get close to that sound with the other wah, I know I will have come a lot closer to understanding this circuit.
Title: Wah'ing around - need help
Post by: Boofhead on August 24, 2004, 06:49:33 AM
After ruling out the transistors I think RobB suggestion of swapping the inductors is a good thing to try.  If the sound swaps you can be pretty sure it's due to the inductors.

(PS: the DC test doesn't quite rule out the gain of the second transistor, not that I would expect it to be a big factor)
Title: Wah'ing around - need help
Post by: aron on August 24, 2004, 08:33:34 PM
OK, I ordered some yellow inductors and a few Fulltone pots. We will see how the inductor affects this wah.
Title: Wah'ing around - need help
Post by: Fret Wire on August 24, 2004, 09:01:21 PM
You'll like em' both. Actually, the Fulltone pot is cheap enough to use as a standard replacement.

It's funny.... in their ads, Dunlop says the Yellow inductor has the Clapton/Hendrix/Page sound (ok, I'll give em that), and the Red (clean) has the Frampton sound. Frampton? I think of funk players when I think of a clean wah sound.
Title: Wah'ing around - need help
Post by: Lonestarjohnny on August 25, 2004, 12:36:26 AM
http://www.cedist.com/
That's It,
Johnny
Title: Wah'ing around - need help
Post by: Fret Wire on August 25, 2004, 12:43:28 AM
Thanks JD, they look a lot alike, are they the same owner or outfit? Even the page with wah stuff looks the same. You just enter "wah" in the search field.

http://www.tubesandmore.com/
Title: Wah'ing around - need help
Post by: Lonestarjohnny on August 25, 2004, 12:56:26 AM
I don't think so, but who know's for sure anymore, they may all be owned by McDonald's, LOL, and I do have to disagree with cap's going bad, they can shape the sound of any circuit from good to bad, no more than it cost to replace the old one's, i can't see the Whodo, if you had to pay some snake charmer boofoo dollar's to do it, yes then it would be a pain, but this is a DIY site, I can do it myself, not be'in onery, just staten the fact's, have fun,  :D  :D  :D
Johnny
Title: Wah'ing around - need help
Post by: Fret Wire on August 25, 2004, 01:10:06 AM
:?:  :?: I think Aron's past caps, and has it narrowed down to the inductor. Is that what you meant?  And Santa...I mean Aron-Claus :twisted:  is going to be carrying Yellow Fasel inductors soon :D :D Thanks for putting in a good word for the Yellows. :)