Build Your Own Clone Message Board

Hello
I have put together a wah kit that isn't functioning. It works in true bypass, but not when engaged. Absolute silence. Not sure where to look first for what I've done wrong. I've looked over all my solder joints, and while not pristine do some to be working. I've taken a meter and checked from one to another.

After having trouble I came here for tips on what to look for. I realized I hadn't done 2 things. I didn't actually check the resistors before installing them. I just used the contents sheet. I also didn't preset the pots. Is that still possible or will the circuit throw the readings off? Here are some pics. Let me know what you see.

Thanks

Matt

More Pics

Your in and out wires from the switch to the board are switched. Also you need to reflow all of the solder joints at the off board wiring part of the pcb.
Resistors look good.

Yeah I soldered those wires with the board installed (on my lunch break in a hurry). Didn't even think about those being switched. Glad you noticed that. I'll fix that and report back. Will probably redo the switch to the new way mentioned on here also.

Btw what would it require to wire in a LED? I'm not worried about the mounting part. Just where would I power from and what resistors (ect.) might be needed?

Thanks again.


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4.7K to +9v
Other end of 4.7K to LED anode (longer lead on LED)
LED cathode to unused switch pole (lead next to flat on LED case)
Unused switch terminal (on the side opposite to the bypass link across the other two terminals) to circuit ground.

Be aware that adding a LED will increase the battery drain / shorten life a little (if you use battery power). You can minimise this by using a very high brightness LED and increasing the 4.7K to the point where the LED is still bright enough to see.

Awesome. That will be one of the next things. However.....

Well I got it to work. Kind of. It only works the first time I turn it on. After that I have to remove the power. Then it works again the first time. Until I remove power. Fwiw I am using a pedal board with power (footnote by skb). I'll try a battery and see if that changes anything.

And to clarify not working. It is passing the guitar signal. It just doesn't sweep. I'm playing through the 8" speaker in the pedal board so it's hard to tell what it's doing. It def changes the tone. Maybe like it's stick in the heel down position.

Also would re-wiring the switch change this? I haven't re-wired it as of yet.

Thanks again.

Matt


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When you corrected the input and output connections what did you actually do? Did you just flip the purple and orange wire connections on the PCB?

When you say it only works the first time you turn it on do you mean with it switched to wah mode on the foot switch you apply power and rocking the treadle sort of does something until you switch to bypass and then back again and .. then what .. no signal or just the treadle has no effect ?

Or do you mean something else entirely, like you power it up and it momentarily seems to do something ... then it doesn't?

All your components seems to be in the right place but of course we can't see if you have all the preset trimmer values in the right positions. There are so many parameters that are adjusted by trimmers in this pedal that the trimmer settings can make a big difference on what the pedal actually does. And then the values of the trimmers varies between a 1K and a 200K. You only need to have got two of those in the wrong positions and it would have a huge effect on how the pedal behaved.

I switched the wires at the pcb. I also desoldered and resoldered some of the other leads that had way too much solder. Now when I first turn on the wah it works fine. Can adjust the trim pots and hear them work. Sounds great. Click the switch and bypass works. Click the switch again and the treadle doesn't change anything. Sounds like it's in the heel down position regardless of where it actually is. Can adjust the trim pots but it sounds the same. No change. Click the switch again bypass works. Click again and it is stuck in the heel down sound.

The only way it "wahs" again is to disconnect and reconnect power. Then it works once and after that only heel down sound as described above.

Double checked the main pot to make sure it wasn't at the end of it's range with the treadle at either end of its range. Tried wiggle all the components to see if something was loose. Not sure what else to try.

If you need me to check anything let me know. I have a meter and know how to use it. Not a complete novice. Just an effects pedal novice. I can wire a Harley from scratch.


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Still think its not wired correctly. Verify your wiring and please provide fresh pics with the same detail as your previous ones.

That is very peculiar behaviour indeed. Apart from the, now corrected, input output wire flip I can't see anything obviously wrong with your build. Have you tried the pedal with a battery yet? If you are using an external supply it is just possible that is shutting down on you.

Still haven't taken pics. Will ASAP.

Yes I have tried battery power with the same results. Forgot to mention that. I have no doubt I've goofed somewhere, but don't understand either. As mentioned I work on bikes for a living and I hate "intermittent" problems. Especially electric ones. They are often simple, but finding it can take forever. Lol.


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K. Got to play with it a bit more. Makes a bit more sense. It works at first but slowly fades to the heel down sound. The switching it off and on doesn't matter. If I turn the switch to on and apply power it works but slowly quits "wah'ing" with the treadle. I guess I hadn't left it on long enough to realize that. I kept bypassing as it was "fading away". Then turned it back on and it didn't work.

Doesn't really help me. Makes me think it may be in the wiring to/from the pot? Any other ideas?


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Seems more like a power supply problem or a problem with one of the electrolytic capacitors to me.

What is odd is that the 4.7uF cap is marked in the parts list and on the PCB as NON-POLARIZED. I can't see any reason why that should be. A normal electrolytic with its negative terminal connected to ground should work perfectly well in that position.That is what you will find in the original Vox circuit.

I suppose the other thing it could be is a bad joint on the PCB where when the power is applied, the circuit is biased such that it provides enough gain for the capacitor multiplier to allow the tuning of the resonant circuit to change as the treadle is moved. Then as various capacitors charge up the circuit conditions change and you no longer get the multiplier effect. Leaving it turned on for a little while and measuring the bias voltages at the collector of the first transistor, emitter of the second and at the output pin of the op-amp would show if this was the case. And you could compare those readings with those taken at the same points right after power is applied.

You could also try just swapping the transistors around to the other socket. If the behaviour changes this may provide a clue.

Won't bore you with details, but I haven't had a chance to bust out a meter. However I did get a chance to swap the transistors. Didn't seem to change anything. However I just swapped them, powered up, switched it on and no wah. Just heel down sound.

Maybe tomorrow I can get some measurements and we can go from there.


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