Homebuilt Dunlop Wah- No Wah?

vfr800fiman · June 27, 2006, 01:02:55 PM

Hi all-
So I built the "Original Crybaby" Wah circuit after seeing as it was very simple, but I have a problem with
the circuit. In the meantime I've been reading R.G. Keen's web site on Wah technology, very interesting.

I get VERY low output from the effect, and the potentiometer just gives slightly more volume
in one direction than the other. I'm also using a small audio transformer for the inductor (temporarily so no comments please).
I also noticed that after swapping a bunch of transistors (2N3904's) I get slightly more volume with
some combinations that with others. I kind of expected this as the Hfe ratings are probably all slightly
different.

The circuit is the only thing in between the guitar and the amp. The amp I'm using (just on the bench)
is just a little 386-based Rat Shack unit. I started with the audio probe method of troubleshooting,
and I'm getting plenty of amplification from the collector of Q1 (2N3904).
However, I loose the signal on the opposite side of the .001uF cap going to the 100k pot, and this is where the
output is taken from.

Any ideas as to where to look next? My only thought is to try it with a "real" amplifier as maybe the 386-based
one is having some affect on the signal.

I kind of gave-up troubleshooting last night and will pick it up again tonight.

And no one give me that "It's cheaper to buy one than build one" crap. I don't learn anything that way

RDV · June 27, 2006, 01:46:49 PM

Pinout?

It should be wah-ing through that amp so that's not it.

A wah circuit was my 1st build. I had to troubleshoot a while till it worked.

What inductor are we using?

There's also been many a post about this very problem so the search function could very well turn up something that will help.

Good luck.

RDV

RDV · June 27, 2006, 01:58:26 PM

Check polarity of the 4.7µF cap, negative should go to ground.

HTH

RDV

vfr800fiman · June 27, 2006, 02:10:07 PM

Hi RDV, thanks for the response.

If you are referring to the transistor pinout, that was the first thing I checked (been known to do that on occasion)

Like I said in my post, I'm using the Radio Shack audio Xformer recommended by R.G. Keen (for now). Will this cause the Wah
not to work correctly?

I started with the search function (as I always do), and it was mostly about troubleshooting stock Dunlop pedals. I suppose
it might help me though, I'll re-scan the results.

I'll check the polarity of the 4.7uF cap again just to make sure. I did get it out of my "junk bin", so maybe it's not good.

Thanks for all the suggestions.
Glenn

kingkryak · June 27, 2006, 02:44:51 PM

when I built my first wah I used a radio shack transformer and it worked fine. I also noticed that when I removed the ground from the 4.7uf polarized cap it cancelled the wah and worked somewhat like a volume pedal. Also check the diagram of the transformer you used it should be on the back of the package. i got the most wah response by using the primary and secondary wired in series.

vfr800fiman · June 27, 2006, 03:23:48 PM

Okay, it's good to know that the Radio Shack xformer worked for you.
I don't have the windings in series, I will try that. I'm using the primary
winding (without the center tap).

Looks like it's time to look at that 4.7uF elect. cap closer.

Anyone ever wound their own inductor for this effect? I'm pretty good at
making my own inductors, although mostly air-core for amateur radio stuff like this:
http://webpages.charter.net/porkchop/radio/loose_coupler1.jpg

Thanks!
Glenn

RDV · June 27, 2006, 03:59:25 PM

The radio Shack transformer will work, but with limited results. It'll be a very mild wah, but it will wah.

The cap is definitely where to look. If it's not that then you'll have to do more troubleshooting.

You should definitely wind your own if you already do that.

Porkchop, eh? Cool handle!

RDV

vfr800fiman · June 27, 2006, 04:15:48 PM

Yes, I figured that the xformer was not the right thing, but good for experimenting.
Thanks for all the suggestions!

QuotePorkchop, eh? Cool handle!

Yes, My Father had quite the sense of humor (he thought)

Paul Marossy · June 27, 2006, 04:54:19 PM

I think you need to get a real wah inductor - that's what makes it a resonant circuit. It won't be very resonant with the wrong type of inductor in there.

vfr800fiman · June 27, 2006, 05:00:12 PM

Hi Paul-
Yes, I know it's not the "correct" thing, I'm just fooling around with
parts that I had on hand. I'll probably wind one pretty soon.
Thanks.
Glenn

Paul Marossy · June 27, 2006, 05:33:47 PM

QuoteYes, I know it's not the "correct" thing, I'm just fooling around with
parts that I had on hand.

I know. I'm just getting straight to the point.

alderbody · June 28, 2006, 06:21:49 AM

QuoteHowever, I loose the signal on the opposite side of the .001uF cap going to the 100k pot, and this is where the
output is taken from.

Excuse me, but should there be any .001uF cap in there?
All film caps in that design are .22uF and .01uF.
Is it a typo or ...not?

...but i would check the 4.7uF electro, too. (crybabies had a 4uF in there, right?)

and get a decent inductor

vfr800fiman · June 28, 2006, 07:18:31 AM

QuoteExcuse me, but should there be any .001uF cap in there?
All film caps in that design are .22uF and .01uF.
Is it a typo or ...not?

The VOX uses .22uF, but the Crybaby uses the .001uF (connects to one side of the Wah pot).
While I'm on this subject, does anyone notice any difference between the sound of the VOX
vs. the Crybaby? The component changes are few between the two. The big difference I see
are the 1k resistor, the .0011 cap, and the 1N4148 diode in the power rail.

Quote...but i would check the 4.7uF electro, too. (crybabies had a 4uF in there, right?)

The Crybaby also uses the 4.7uF, at least in the schematics that I've seen.

Quoteand get a decent inductor

Point taken

alderbody · June 28, 2006, 08:54:01 AM

i don't quite recall a wah with a .001uF
I have a schematic of the "original crybaby" and it doesn't show such a cap. (

?)

maybe if you posted your schematic...

btw, the old wah pedals used to have 4uF caps.

alderbody · June 28, 2006, 09:01:41 AM

OK, i found the schematic you probably used.

my bad on this...

...how about that inductor?....

waldo041 · June 28, 2006, 09:20:26 AM

check the resistance of the xformer you are using. ideally you want it around 30 ohm's. anything under 20 ohms may work but will not be good. also what is the mH of the transformer you are using?

hope this help's

peace,
waldo

vfr800fiman · June 28, 2006, 10:41:36 AM

Quote from: waldo041 on June 28, 2006, 09:20:26 AM
check the resistance of the xformer you are using. ideally you want it around 30 ohm's. anything under 20 ohms may work but will not be good. also what is the mH of the transformer you are using?

Hi Waldo-
I'll check the resistance, but I don't have an inductance function on my DMM.
I'll have to bring it to work to do that measurement.
Thanks for the resistance number.
Glenn

Paul Marossy · June 28, 2006, 11:11:44 AM

If it were me, I would dump that 0.001uF cap and use a 0.22uF - it'll sound fuller that way. I don't think there is much of a difference between the 4uF cap and the 4.7uF cap, but some people hear a difference. To me, it's not enough to be overly concerned about.

waldo041 · June 28, 2006, 12:05:27 PM

Quote from: vfr800fiman on June 28, 2006, 10:41:36 AM
Quote from: waldo041 on June 28, 2006, 09:20:26 AM
check the resistance of the xformer you are using. ideally you want it around 30 ohm's. anything under 20 ohms may work but will not be good. also what is the mH of the transformer you are using?

Hi Waldo-
I'll check the resistance, but I don't have an inductance function on my DMM.
I'll have to bring it to work to do that measurement.
Thanks for the resistance number.
Glenn

i am sure you know the inductance should be around 500mh or higher will be fine. you may need to string 2 or 3 together to reach the inductance you want. keep in mind these are optimium numbers for an inductor, so you don't need to be exact to make it work. in the ballpark is good. here is a great wah inductor chart.

http://homepage.ntlworld.com/s.castledine/greenfuz/inductor.html

also, i have wound my own halo inductor's from the kit and wire from small bear and the instruction's there. with the patience and practice anyone can do this.

is this the circuit you are using?
http://www.geocities.com/j4_student/crybaby.gif

peace,
waldo

vfr800fiman · June 28, 2006, 01:54:40 PM

Yes, that's the circuit I'm using.

My biggest concern is not the lack of wah, but the extremely low output on the potentiometer side of the
.001 capacitor (this is where the output is taken for the effect). The volume is VERY loud at the collector of Q1, which I would expect if the xsistor is working
correctly. I guess I just don't understand why the volume is reduced so much after it passes through the
.001uF cap. Shouldn't the cap allow the signal through and just block any DC?

BTW, I'm using those very tiny capacitors (~3/16"long X 1/8"high for the body) labeled 102, but I'm not sure of the construction material. I've used these on other effects projects with no issues, but I thought I'd just mention it.

Can I still use the 2N3904's and change the rest of the components to the VOX circuit? or do I have to also switch to MPS-A18's? I would assume the
bias is different for these xsistors, so maybe I have to change the resistor values as well?

Thanks, I will be winding my own inductor. Anyone ever try using a toroidal ferrite core for this component?

Glenn

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Homebuilt Dunlop Wah- No Wah?