wah doesn't wah

[orangedrop]

I don't get any answers over at the BYOC forum - I thought maybe I could get some help here:

I built a BYOC Wah several years ago. I've been very satisfied with it. It doesn't get used very much (but a bit every other day).
Suddenly it's just dead - no wah. There is a volume drop when the wah is engaged, when rocking the pedal it's more like a volume pedal, but there is a small increase in treble as well. I swapped the 4,7 uF tantal and the 10 uF Elyt. No difference. I've poked around all components - no effect.

Is it the op amp? the inductor? Any ideas? 

All thoughts are much appreciated   

[R.G.]

1. We'll need you to post or give a link to the schematic. The circuit may have ideosyncrasies.
2. If it happens to be a semi-stock circuit like the Vox inductor-style wah, what you are describing is probably a bad solder joint letting go.

[orangedrop]

R.G - Thanks!

I'm trying to upload the image but I can't (How to do that?)
The schem is on the BYOC website - page 13 Could you please look there?
http://buildyourownclone.com/wahinstructions.pdf

I tried with another inductor (Fulltone Clyde) I then get the hollow sound but no wah effect when turning the pot.
It's like a fixed wah.

I also resoldered everthing - no difference. (Rather time consuming).

Bjorn

[R.G.]

I'm trying to upload the image but I can't (How to do that?)

You can't. It has to be somewhere on the web and then you can link to it - so the link works for what I need.

I tried with another inductor (Fulltone Clyde) I then get the hollow sound but no wah effect when turning the pot.
It's like a fixed wah.

Hmmm. New problem.

That is one complicated board to wire for a beginner. How do you have it wired, what options, etc?

If it's not soldering, then the next most likely thing is wiring. Both the "no wah" and "fixed wah" conditions have to do with the rocker pot and/or second transistor not working properly. Check wiring especially in that area.

It's funny - the use of an opamp buffer makes the second transistor  and the appurtenant resistors and caps completely redundant. But that's neither here nor there.

[Earthscum]

It's funny - the use of an opamp buffer makes the second transistor  and the appurtenant resistors and caps completely redundant. But that's neither here nor there.

So with the OPA buffer, you could take out the transistor, 470k, E resistor, C resistor, cap to base, and just connect the .01uF to the wiper of the pot, as well you should be able to lose the OPA's biasing network, and the decoupling cap, and take a DC coupled signal straight off of Q1's Collector. Correct?

I'm just asking since it was brought up... not trying to confuse you or anything, orangedrop.

[orangedrop]

Well, thank you both!

I didn't do any mods. Just tweaked it with the small pots inside. I changed the wah-pot some time ago - so it should be OK.
The wah actually sounds really good, it's worth bringing back to life again.

I AM confused as is - but nevertheless I've built several effects and amps as well (Tweed Deluxe, 18W, Deluxe Reverb) - but I don't have much understanding of electronics. I've read a lot of RG stuff BTW - thank you for all that info!

"It's funny - the use of an opamp buffer makes the second transistor  and the appurtenant resistors and caps completely redundant."
- When I look at the schem (with the buffer opamp) I can only see one trannie?? Does this mean that I can swap the trannies as a test?

One question - the opamp is solely for the buffer? and it's a singel opamp which means that I cant use a JRC 4558?

Bjorn

[DavenPaget]

Well, thank you both!

I didn't do any mods. Just tweaked it with the small pots inside. I changed the wah-pot some time ago - so it should be OK.
The wah actually sounds really good, it's worth bringing back to life again.

I AM confused as is - but nevertheless I've built several effects and amps as well (Tweed Deluxe, 18W, Deluxe Reverb) - but I don't have much understanding of electronics. I've read a lot of RG stuff BTW - thank you for all that info!

"It's funny - the use of an opamp buffer makes the second transistor  and the appurtenant resistors and caps completely redundant."
- When I look at the schem (with the buffer opamp) I can only see one trannie?? Does this mean that I can swap the trannies as a test?

One question - the opamp is solely for the buffer? and it's a singel opamp which means that I cant use a JRC 4558?

Bjorn

OH SHIT ! YOU SCREWED UP ! Dual's and single's have different pinouts . Try a TL071 or a LF353 or pretty much any single opamp you like , try to use JFET types like those i mentioned .

[Earthscum]

OH sh*t ! YOU SCREWED UP ! Dual's and single's have different pinouts . Try a TL071 or a LF353 or pretty much any single opamp you like , try to use JFET types like those i mentioned .

Lol! Maybe we should ask what he used before assuming that he dropped in a dual.    Nevertheless, I laughed and had about 100 personal moments flash through my head when I read that.

[R.G.]

So with the OPA buffer, you could take out the transistor, 470k, E resistor, C resistor, cap to base, and just connect the .01uF to the wiper of the pot, as well you should be able to lose the OPA's biasing network, and the decoupling cap, and take a DC coupled signal straight off of Q1's Collector. Correct?

Actually, I take that back. The buffer in this case doesn't buffer the wah output, just the output back to the filter. But a dual opamp would do the job.
Sorry. Too much Christmas dinner.    

One question - the opamp is solely for the buffer? and it's a singel opamp which means that I cant use a JRC 4558?

Yes. The pinout for duals and singles is different. I generally don't use singles at all, because duals cost about the same. However, once the PCB sets the pinout, you are forced to use a single, not a dual.

If you don't find a wiring issue, go read and follow "Debugging: what to do when it doesn't work."

[orangedrop]

Well, I did not "use" the dual opamp  I only asked if it could be done - I suspected not.

Anyway, problem solved - actually two problems.
1. I swapped the transistors and got it to work on a ON/OFF basis when pressing the trannie down into the socket (I always mount op amps and trannies in sockets).
2. I went trough all the solder joints again - and now it works, I've must have missed one bad sodler joint as RG suggested.

A follow up question: When I swap the trannies back - it still doesn't work. Why is that?

[paulyy]

A follow up question: When I swap the trannies back - it still doesn't work. Why is that?
[/quote]

Hmmm... What kind of trannies are they?

[orangedrop]

2 x CV10805

[R.G.]

1. I swapped the transistors and got it to work on a ON/OFF basis when pressing the trannie down into the socket (I always mount op amps and trannies in sockets).
...
A follow up question: When I swap the trannies back - it still doesn't work. Why is that?

It is very likely that there is another intermittent joint, or that one of your sockets is intermittent.

I used to use sockets for ICs and transistors. I kind of grew out of it because I developed the soldering skill over years to both put in and take out parts well enough to not need them. These days, good sockets cost as much as the devices you plug in in many cases, and bad sockets are worse than no socket at all.

But if you use them, get quality sockets. Use the machined-pin style, and be sure the size wires you plug in are within the size the socket is designed to accept. Too small and they won't hold firm. Too large and the contacts are deformed and can break or otherwise be intermittent.

[paulyy]

2 x CV10805

Hmm...Should work but you could do what R.G. was saying. I've had that issue before with sockets.

[orangedrop]

Thank you all for your help!

Happy New Year