Wah with the dreaded volume effect.

[Organtis]

So I have a crybaby classic wah with fasel.  I think it's a 2006 almost all pcb. I bought this as a fixer upper.  I got it for a good price but it was missing a pot,  I went with hot potz 2.  After recieving it I found it to be much more.  I had to replace a bad switch, the rubber feet and the rack tensioner.

So after all this I'm $60 deep in this and it still sounds like a volume pedal. I've noticed however that  c2 and c4 are missing they are supposed to be 4.7uf and I have some 2.2uf laying around,  should I try those or look at something else like testing the inductor?

[JustinFun]

Do you mean they're missing per the schematic or per the board?

I only ask because having seen a few dunlop wahs they seem to use the same board and so they're often apparently part populated if you look at the board.

[R.G.]

I've noticed however that  c2 and c4 are missing they are supposed to be 4.7uf and I have some 2.2uf laying around,  should I try those or look at something else like testing the inductor?

Missing bad capacitors will convert the wah circuit into a (clumsy) volume pedal. The ancient "Boomerang" used a switch to do this for an effect, in fact. Put in replacement caps. That should fix some, maybe all of the problems.

I symphathize - you were taken advantage of. Some budding boy genius tried to "modify" the pedal, got in too deep, and dumped it on you.

[Organtis]

Well I did it to myself......  I didn't have to buy all the parts,  I could have flipped it back.  I only paid 15+shipping, the parts cost me more.

The bad part is I don't even want to sell this now unless I use it for 6 months. It's kind of a challenge now but I'm wondering if I could use the 2.2uf in this circuit or see if radio shack has any or wait another week for parts.

[tomer629]

I'm having this problem too, but with a new Mowah build. Im using brand new name brand caps from mouser so I think I *Should* be good there.

Anyone know any other reasons for this volume effect instead of bad caps? It seems to be a common issue. Just wondering if its usually bad caps or if it could be many different things.

Sorry Organits don't mean to highjack the thread. Did yours work after putting the caps in?

[R.G.]

Yes, someone knows other reasons.

You could read The Technology of Wah Pedals ( http://www.geofex.com/article_folders/wahpedl/wahped.htm ) if you want to understand the wah circuit.

The wah circuit uses the wah pot as a volume control, but the wiper signal is fed to a feedback path, not the output jack. There are about 57 different things in that feedback path that could cause the volume-control action to happen.

[Organtis]

Well here is where I am at.  I am trying to heat up where the smt components were and my solder isn't taking.  I'm just burning up the clearcoating. I'm thinking that I need to scrap off any existing solder on the pads before the solder will stick but I thought I would check back before doing that. 

I will say however that holding the caps in place did nothing but I don't know that I was getting connectivity. At this point I just don't want to risk ruining the board.

[Transmogrifox]

You need to have solder braid and a hot soldering iron to clean up the pads.  Don't try to scrape it off cool or you are likely to damage the board. Also if solder on the pad does not melt you might not be using the right tip.  A chisel tip is better than a pencil tip for this.  If you have a sacrificial pencil tip you can bend it over at the end so you can get more surface area contact with the board.  Also use solder to melt solder.  I mean, put your tip on the board, and add some solder to it.  The little ball of melted solder helps transfer heat from your iron to the board.

You really need to be careful with the SMT pads because they will delaminate from the board if you apply pressure and heat for too much time.   High temperatures for short durations with little or no pressure is the best.

This thread might help:
http://www.diystompboxes.com/smfforum/index.php?topic=98281.0

There are about 57 different things in that feedback path that could cause the volume-control action to happen.

Did you get that number from a ketchup bottle?

Regardless I agree volume control effect has more than a few possible causes, but if you have a schematic accurate to the part reference designators you can quickly find what's wrong by systematically checking each part.  It's easier to check some 20 components than to troubleshoot N^20 possible combinations of components.

A longer but worthwhile road is to take RG's suggestion and use the wonderful resources here to become somebody who knows what the hell he's doing