Help with Clyde Mccoy Wah

[brown5629]

Hey,

I'm building a Clyde Mccoy circuit with an output buffer, using the schematics and layouts found at Fuzz Central. http://fuzzcentral.ssguitar.com/mccoy.php
Well, I've wired it all together, however only the original signal passes through. When the footswitch is pressed, the signal cuts out completly.

I tested the voltages of the transistors, checked for continuity and shorts about a million times, and have tested with the audio probe, but I am still not sure where the problem lies.

input voltage: 8.90
Here are the transistor voltages:
Q1:
C - 4.51
B - .63
E - .09

Q2:
C - 8.59
B - 2.77
E - 3.28

Q3 (JFET in output buffer):
D - 8.89
S - 8.14
G - 8.16

It looks like Q1 is fine. But I'm not sure about the other two.

Using the audio probe I noticed a couple of odd things. Right before the .05 uF in the output buffer, there is a clear signal, however a bit more bassy than
the original signal. At that same area, when I spun the pot, it acted like a volume pot. I've read that this is usually caused by a bad electrolytic, but can this be the only problem? I believe there must be something else. Thanks for all of your help.

[jonathan perez]

triple check your offboard wiring.

[brown5629]

Well I just checked all of the offboard wiring with a multimeter, and everything seemed to be in order and wired correctly. Any other ideas? Thanks again.

[tcobretti]

I would say to first double check your transistor voltages, and if they are corrrect, something is wrong.  The base should pretty much always be .6v higher than the emitter, so Q2 looks suspect.  I am thinking Q3 might be a problem also, but I haven't studied JFET biasing at all, so someone more educated will have to comment on that one.  I'd check very carefully for solder bridges around Q2.  Assuming you get Q2 fixed, I would then audio probe it before the buffer to see if the buffer is also a problem.

[brown5629]

Ok, so I double checked the transistor values I posted, and it looks like they are correct. Then, it looks like Q2's emitter is getting too much voltage. This seems to point to the 4 uF NP electrolytic to ground. However, I'm using 4.7uF polar, not the 4uF NP. Should I replace it for another polar, or attempt to find a 4uf NP? Also, is there anywhere else there could be a problem?

[tcobretti]

I don't think the type of electro is the problem, but you might try another of the same value to be certain it isn't bad.  Most wahs have polar electros in there, so the NP is not the problem.  I am not smart enough to troubleshoot what could be causing the problem, but I don't think the pedal will work til you sort it out.

My Vox's Q2 voltages are 7.8 C, 3.4 B, 2.8 E. 

[tcobretti]

Maybe a stupid question, but you did notice that the transistors are oriented in opposite directions, right?

[jonathan perez]

Maybe a stupid question, but you did notice that the transistors are oriented in opposite directions, right?

does the inductor work?

wire it up sans buffer, and see if it works.

[brown5629]

Hmm, Ill have to check that, thanks. Is the inductor directional? (I don't believe it is,  but just checking)

[brown5629]

Also, I replaced the electrolytic with another with the same value, but there was no change at all. It Looks like it might be the Whipple inductor... Ill have to check it.

[brown5629]

Thanks for checking, but yes, the transistors are in the correct directions.

[jaytee]

The jfet buffer voltages look all wrong. It should be more like, D - 9v. S - 4.5v. G - 0v. The gate is connected to ground through the 1M resistor. There should be hardly any current flowing so should read 0v at the gate. The buffer is isolated from dc by the 2 caps before and after it so even if you have other things wrong the buffer should still work. Check you have everything connected right to the jfet. If so I'm guessing you have it in the wrong way round. Check the pinouts from a datasheet.

[brown5629]

Hey, thanks for the heads up. It turns out the JFET was backwards. I changed it out, and the buffer is working perfectly. The JFET values are now:

D - 8.70V, S - 7.90V, G - 0V

Also, this seemed to have fixed Q2:
E - 3.29V, B - 3.72V, C - 8,5V

However, the circuit still acts like a volume pedal when the potentiometer is turned! I changed out the electrolytic already, so that can't be the problem. I don't know much about inductors. Does its orientation matter ( such as spinning it 90 or 180 degrees ) ?

[Paul Marossy]

Orientation doesn't matter on the inductor. Maybe you got a bad one? One way to check is to pull it off of the circuit board and test it for continuity and DC resistance.

Also, are you sure that it is actually in the circuit and not just soldered to a dead end?

[brown5629]

I took the inductor out (I'm using the Whipple from Mike from Brooklyn) and the circuit sounds exactly the same (essentially just a volume knob) I checked the resistance and continuity of the inductor (i was told it was supposed to be 30ohms but I don't really understand how the leads are wired, i don't know much about inductors) In any case, none of the leads are connected and they all have infinite resistance between them so it seems like the inductor is broken, I plan on returning it but i figured I'd check if anyone thinks there's something I'm missing. Thanks.

[Paul Marossy]

If you're getting infinite resistance, then your inductor is faulty. Are both of those tiny wires connected to the posts that you solder to? Sometimes you can fix those if they came off at the post.

[jaytee]

I have a 'whipple in my wah' it sounds great. Have a look at the pins on the inductor. Only 2 of them are connected. The other 2 arn't connected to anything. If you look carefully you can see the fine wire coming from the coil and connecting to each of the 2 pins. Test between those 2 for resistance. Sometimes you get a bit of crud on a pin and may have to scrape it a bit to get a reading even if it 'looks' clean. If you can get a reading off it you probably had the inductor in the wrong way round by 90 degrees.

[Paul Marossy]

The other 2 arn't connected to anything.

And if those two pins are soldered to the circuit board instead of the pins with the wires connected to them, the inductor won't be in the circuit... 

[brown5629]

Hey so I checked for/fixed those tiny wires in the inductor, and it worked great! Thanks to everyone for your help. I couldn't have finished it without you.

[Paul Marossy]

Hey so I checked for/fixed those tiny wires in the inductor, and it worked great! Thanks to everyone for your help. I couldn't have finished it without you.

Aha! That was the culprit after all. Wah on, dude!