Wah clone squealing at heel down position

[marcoharder]

Hi! I recently completed a McCoy wah clone that I got from this site: http://fuzzcentral.ssguitar.com/mccoy.php.

However, BC108's are very hard to find in the Philippines so I used a pair of 2N3094 NPN Silicon transistors. I was able to make the wah work, except that it emits a very loud squeal in the heel down position. Is this because I used a lower gain transistor? Or should I bias these transistors and change the values of resistors to work with the 2N3094's?

Your help would be greatly appreciated.

Marco
Philippines

[rockgardenlove]

I think somebody else has reported squealing with 2n3904s.  I would try some higher gain transistors.  The wah circuit isn't fussy, just sub in some higher gain BJTs.

Cheers!

[Paul Perry (Frostwave)]

First, I would try disconnecting the pot & trying it with another pot (connected by wires for the moment, and hand operated). Just in case the pot is faulty, and the wiper loses contact at one end of the travel.
Another thing: before it squeals, is it working OK? Can you hear a 'wah' filter sweep over the rest of the range?

[marcoharder]

First, I would try disconnecting the pot & trying it with another pot (connected by wires for the moment, and hand operated). Just in case the pot is faulty, and the wiper loses contact at one end of the travel.
Another thing: before it squeals, is it working OK? Can you hear a 'wah' filter sweep over the rest of the range?

Yea, it does wah and it did when I finished - with the squeals and all.


If you start at the heel down position, you'd hear a squeal even when you play then as you rock it the squeal dies out and the wah effect is becoming mor prominent. The sound of the wah is awesome - I just need to remove that squeal.

[marcoharder]

I think somebody else has reported squealing with 2n3904s.  I would try some higher gain transistors.  The wah circuit isn't fussy, just sub in some higher gain BJTs.

Cheers!

I see. Any common trannies you can suggest? How about an MPS-A13? 2N2222? 2N5088?

[tcobretti]

MPSA13 - probly not

2N2222 - might work.  Pretty low HFE if memory serves, so may squeal like the 3904s.

5088 - This is your best bet.  Should work fine if all is well in the pedal.

[Paul Marossy]

Here's some thoughts:

1 How did you build it? Did you use the PCB at that website?
2 Are you sure that maybe your inductor isn't microphonic?
3 Does it do this with a clean guitar sound?
4 How are you powering the circuit?
5 Are you sure that you have the input and output jacks wired correctly?

[marcoharder]

Okay, here are my answers:

1. I built it using the PCB diagram there.
2. I have no idea whether the inductor is microphonic or not but the inductor that I'm using is the Halo-clone that I bought from smallbearelec.com
3. No, it doesn't.
4. I'm using a new 9v battery.
5. I'm pretty sure I wired it correctly since it's wah-ing at a particular range and it only starts to squeal at heel down.

Thanks Paul!

Here's some thoughts:

1 How did you build it? Did you use the PCB at that website?
2 Are you sure that maybe your inductor isn't microphonic?
3 Does it do this with a clean guitar sound?
4 How are you powering the circuit?
5 Are you sure that you have the input and output jacks wired correctly?

[jonathan perez]

i dont think the trannies are the problem. make sure youve got the right values in the right places, and check the orientation of the electro.

[enigmur]

Are you using it into any other pedal?

Mine did exactly what yours is doing when going into my fuzz face at one stage. It wasnt the wah at all.

I assume you are testing straight into an amp though.

[Paul Perry (Frostwave)]

Making the 22K resistor smaller should drop gain, if that is the problem.

[marcoharder]

I did it straight through a tube amp.

Are you using it into any other pedal?

Mine did exactly what yours is doing when going into my fuzz face at one stage. It wasnt the wah at all.

I assume you are testing straight into an amp though.

[marcoharder]

Okay, will do that. BTW, when you say electro do you mean the electronic components? or something else?

i dont think the trannies are the problem. make sure youve got the right values in the right places, and check the orientation of the electro.

[marcoharder]

I see. I will try that out. Thanks man!

Making the 22K resistor smaller should drop gain, if that is the problem.

[rockgardenlove]

BOM means that 4.7uF electrolytic capacitor.

[R.G.]

I would put a BFC* across the power supply to start with. The classic wah has more gain at bass frequencies and it sounds like this could be getting feedback through the power supply.

In fact, a 1K between +9V and the collector of the second transistor and a BFC to ground from there would probably be better.

Start with that.



*BFC = Big Freaking Capacitor, 100 to 1000uF

[Paul Perry (Frostwave)]

Of course, RG is right. But, it raises the interesting point - if one deliberately adds a  switched resistor in series with the power supply, maybe this will give a 'siren' option!
"everybody, outta da pool!"

[marcoharder]

Thanks RG! I'll try that out later, one by one.

I would put a BFC* across the power supply to start with. The classic wah has more gain at bass frequencies and it sounds like this could be getting feedback through the power supply.

In fact, a 1K between +9V and the collector of the second transistor and a BFC to ground from there would probably be better.

Start with that.



*BFC = Big Freaking Capacitor, 100 to 1000uF

[marcoharder]

Thanks RG! I'll try that out later, one by one.

Just a few questions:

1. Would the BFC be in series and in between the +9v and the 22k resistor that goes to the collector of Q1?
2. The schematic shows that the collector of Q2 already has a 1k resistor that's connected to the +9v. Should I add another or just replace it with a 2k resistor?
3. In regard to the 2nd suggestion, where to I exactly put the BFC? I mean I know that one end will go to ground, but where should the other end go?
4. Should the BFC's be electrolytic and polarized? Or can I just use mylar caps?

Here's the schematic for everyone to refer to:

I would put a BFC* across the power supply to start with. The classic wah has more gain at bass frequencies and it sounds like this could be getting feedback through the power supply.

In fact, a 1K between +9V and the collector of the second transistor and a BFC to ground from there would probably be better.

Start with that.



*BFC = Big Freaking Capacitor, 100 to 1000uF

[Paul Marossy]

it sounds like this could be getting feedback through the power supply.

That was my hunch. I've had it happen to me when using a wall wart and a really high gain distortion pedal called a Boss Metal Zone. That sent it straight into oscillation whenever I tried to use it. It was OK with a clean guitar sound, however...