Help diagnosing a Vox Clyde Wah.

[pedaljunkie]

I hope this is the right place to post..

My bud gave me a relatively new (maybe a year old) Vox Clyde McCoy wah to try and fix for him.  Everything looks spotless on this pedal, and when you plug in to it, it passes signal very well.  Then you click on the switch and the pedal turns on and still passes signal, but acts as a filter only.  The rocker doesn't seem to affect anything at all. 

Obviously, my first guess is the pot, but I've read that the 4.7u cap by the inductor could be the culprit as well.  I also read that if the pot didn't work, that there would be no sound at all.

My question is this:  Since I'm not great with a DMM (but have one and want to learn),    how should I go about testing the points of the circuit or parts so I don't just start replacing what I THINK might be wrong?

(also, I know this sounds ridiculous, but is there a post on here that goes into detail about using a DMM and the different settings and their uses?)

Thanks guys!

[joegagan]

can you give us some internal photos? i am curious what the current spec is. this will also help diagnose, as many of the current dunlops are now true bypass, which makes a difference on the symptoms you describe. the better the detail in the closeups, the better we can help. use good lighting/focus, please.


as far as the meter, i think a lot can be gleaned from the manual that came with it. but you bring up a good point. a 'how-to' on using a multimeter for Fx is probably a good idea as a sticky for this forum.

[pedaljunkie]

As soon as I get home, I'll snap some good quality close ups of the guts.  Thanks for the reply.  (and i will definitely peruse the manual) 

[pedaljunkie]

Alright here are some gut shots of the wah, which I found out is true bypass if this also helps...

[Paul Marossy]

I see a "Q3" , looks like it is not a true bypass wah. And the original Clyde McCoys didn't have a Fasel inductor... 

[DiscoVlad]

Going by what I can see in those photos, the brown and white wires go to the jacks, green and blue are effect in and out. with a dpdt switch wired for true bypass... The purple wire going to the stereo jack looks like it's the ring terminal/ground switch?

The extra transistor is probably a buffer... I'd guess an input buffer like the standard crybaby boards since the output from the pot goes directly to the switch.

[Paul Marossy]

Going by what I can see in those photos, the brown and white wires go to the jacks, green and blue are effect in and out. with a dpdt switch wired for true bypass... The purple wire going to the stereo jack looks like it's the ring terminal/ground switch?

The extra transistor is probably a buffer... I'd guess an input buffer like the standard crybaby boards since the output from the pot goes directly to the switch.

I don't have one of these in front of me to verify anything and have never had my hands on one, but it looks to me like this is just a GCB-95 type circuit with a Fasel inductor (NOT what the original Clyde McCoys had) and Clyde McCoy graphics on it. How disappointing. Apparently it is true bypass from what I have found on the net - " The reissue version is true to the original in most details, including the tone-critical part —- a custom-tuned inductor made by the original manufacturer. It also has some modern enhancements such as a true bypass switch, a newly designed custom-taper potentiometer, and an AC adapter jack." (From the Musicians Friend website)

Where did they get their information on the inductor?!?!?!

[Paul Marossy]

OK, I'm done picking at the reissue Clyde McCoy.

Check the voltages on the transistors, one of them could be bad.

Could also be a bad 4.7uF electro (not likely, but not impossible), or something to do with the pot or the wiring to the pot.

I'm guessing it's a problem associated with Q2.

[joegagan]

pretty sure these were discontinued a few years back. they sounded really good despite the not-so-vintage buffer etc.

these got a bad rap with the public because their 'icar' repro pot wouldn't last through one rendition of voodoo chile before going scratchy.

i would suspect a bad pot, or the aforementioned 4.7 uf cap. also, use your continuity checker to assure everything is connecting from one end to the other on the whole harness.

it is gonna need a new pot anyway, just go ahead and replace it.

nice pics by the way. there are two date codes, one on the switch , one on the pcb. 2005.

[Paul Marossy]

I agree, that pot looks like it would last five minutes before failing. It could be that the pot is bad, but nothing was said about it being scratchy. The voltages on the transistors really need to be verified as being within normal ranges or else everyone is just shooting in the dark with a shotgun.

Also, another thing to check is the continuity on the wires in that wiring harness connector, the ones going to the pot. It may have been compromised or it was barely working when it left the factory and over time vibration, etc. has caused it to fail.

[pedaljunkie]

Thanks you guys! I will check everything out tonight and get some readings on those transistors.  I will order another pot either way, but do any of you have a preference?  I see Hot Potz on PPP.

[joegagan]

This might seem rare but the track record of these pots makes me suspect some kind of internal failure, like the wiper misaligned or lifted in some way.  Your trans bias comment is good as well.     Those harness/connectors are quick-assemble, no wire stripping involved, so, while rare, it also feasible that something intermittent has possibly happened there. When continuity testing, test at final destination of each wire.

[joegagan]

I have been having good success with arteffect icar repros. I have a supply of them , send me a pm, i can hook you up.

[joegagan]

Hotpotz2 is the most durable wah pot i have found. They are no longer available less than20-25,there was a rumor few years back that they were going to be disconinued. I hope this isn't the case.  I haven't tried the mcconopot, but people seem to like it. Mccono has a tutorial at his site about doing regular cleaning of the pot.  This great advice for any of the open type pots with rubber covers.
But ulitmately the hotpotz2 is preferred as they seem to last ten to twenty times longer before needing any maintenence at all.

Note: the arteffect pots are of the same open type as mccono, propot etc, however i do not know where they are actually made.

[Paul Marossy]

+1 on the HotPotzII pots...

[pedaljunkie]

I was also looking at the Area 51 ICAR pot as well.  Are the arteffect pots 200k?  They're getting pretty great reviews as well.

[joegagan]

I was also looking at the Area 51 ICAR pot as well.  Are the arteffect pots 200k?  They're getting pretty great reviews as well.

not familiar with the area 51 pots, but they have a great rep as a company.

yes, the arteffect pots measure out to around 180k to 192k. the vintage 67 icar they used as their model had this value. i recall g teese mentioning a long time ago that the vintage icar he measured was also just under 200k. he mentioned that the higher value may be due to wear(?)
anyway, out of four icar repro pots i have measured (teese rocpot circa 04, vox mccoy RI circa 04, propot from 2010 and the arteffect), they all follow the same taper within 5% or so.

[Paul Marossy]

There's also the "Pro Pot" which measures around 200K. But those won't last long either compared to the Dunlop HotPotz II.  

[joegagan]

propots go scratchy very quickly. have bought at least 4 used wahs that had them, and even tried new ones. up to now i never  did the cleaning thing since i did not want to sell a customer a pedal that needed so much maintenence.
propots also have a poor tab system that sometimes makes the whole pot move around when the gear is pushed. see video.

[Govmnt_Lacky]

@Joe

I just wanted to say THANK YOU for all of the help and knowledge that you contribute to the forumites! 

I know you have assisted me considerably with my wah headaches either directly or indirectly.

You are an invaluable forum resource and I just wanted to take a second to show my appreciation!!!!