Help with vox wah mods

plaiming · August 12, 2006, 08:30:18 PM

im not sure if i should have posted this in the newb area but i figured it would be ok here. this is my first real pedal mod but im not completely new to electronics. this mod has been SLOW in the making. i started with a vox847 pedal i bought used about 8 months ago. i cant remember if i actually tried it or not - but i think i did and i think it was working. i then purchased some 3PDT switches from the store here to make it true bypass. i followed instructions found at various websites and the soldering seemed to go smoothly. i then was going to put in a 9v jack and when drilling the hole in the casing, i punched through with the drill and knocked out my halo inductor and some resistors. it took me until today to get back to the thing. i ordered a red fasel, replaced it on the board and the cut resistors with exact same values from ratshack. everything seems to go smoothly, but when plugging in, it seems to work fine in bypass but when engaging the wah, its really messed up. kind of works like a static/distorted volume pedal. i tried checking all the connections with my meter and the everything looks good. i plugged in a battery and im seeing 8.6v on the pins into the PCB. one thing is that im getting continuity across the red fasel. is this correct? i will post a pic of my pcb job and the switch job.

Paul Marossy · August 13, 2006, 01:05:35 AM

Quoteone thing is that im getting continuity across the red fasel. is this correct?

Nothing to worry about there - those inductors have a low enough DC resistance that it will look like continuity to a DMM. It sounds to me like you have a cold solder joint, a broken track on your PCB or perhaps one of those resistors inadvertently got replaced with the wrong value.

plaiming · August 17, 2006, 01:53:31 AM

hey thanks man. im sorta back in business but im not exactly sure what it was. i rechecked all the traces and everything seemed fine. i notice a litte looseness in the redfasel mount so i resoldered. i also got a fresh duracel that read 9.3v with my meter. put everything back together and now im getting some wah. infact, it didnt sound too bad. a little too much high end on the wah but i havent done any of the other mods (just the fasel and the true bypas) true bypass works great!

one problem remains, after engaging the wah, it sounds ok unless the pedal gets depressed almost down all the way to
the switch. at some point near the bottom, i get a really bad hum/buzz. have you ever heard of such a thing?

could it be that the 3dpt switch is shorter so the wah pot travels further than it is supposed to before shutting off?

-paul

Paul Marossy · August 17, 2006, 10:05:59 AM

Quoteone problem remains, after engaging the wah, it sounds ok unless the pedal gets depressed almost down all the way to the switch. at some point near the bottom, i get a really bad hum/buzz. have you ever heard of such a thing?

Hmm... that's a new one on me. Not sure what could be causing that.

Quotecould it be that the 3dpt switch is shorter so the wah pot travels further than it is supposed to before shutting off?

I don't think so. If that were the case, the pot would reach its far limit and prevent you from switching it on/off. You could try adjusting the pot travel a little bit to tame the highs and possibly make this problem go away at the same time.

plaiming · August 18, 2006, 11:02:12 AM

well, im using a single coil telecaster - and the noise sounds alot like interference you would
hear through the pickups or a noisy power/ground - but it only kicks in on the last little bit of
the pedal.

Paul Marossy · August 18, 2006, 11:04:55 AM

Oh. Well, that sounds like it's just your wah amplifying whatever noise your pickups are picking up. Not much that you can do about that.

plaiming · August 18, 2006, 11:12:07 AM

why do you think that would only happen when the pedal is all the way down and not when im "wah"ing...

Paul Marossy · August 18, 2006, 11:22:52 AM

Quotewhy do you think that would only happen when the pedal is all the way down and not when im "wah"ing...

When say "all the way down", do you mean right before the switch actuates? If so, I would say that it is because it's amplifying the high frequencies more. Does this happen every time, no matter where you are physically or does this happen only in a specific location?

jonathan perez · August 18, 2006, 11:43:45 AM

im not sure what "down" means either. nor have i ever gotten noise with the TOE down.i only get some noise when the HEEL is down, and only if the wah is at the corner of the board.

Paul Marossy · August 18, 2006, 12:03:02 PM

Quotei only get some noise when the HEEL is down

That's just the opposite of me. I hear noise/buzz mostly in the toe down position right before the switch actuates...

plaiming · August 18, 2006, 06:36:26 PM

Quote from: Paul Marossy on August 18, 2006, 12:03:02 PM

That's just the opposite of me. I hear noise/buzz mostly in the toe down position right before the switch actuates...

yes, this is correct. to clarify: i press the toe down to activate the wah circuit. then heel down - and as a i play i toe up and down to "Wah" - now i normally dont have to put the toe all the way down to get the full wah sweep - so no noise. but when im done using the pedal, i go to toe down all the way and de-activate the wah circuit. with the switch. right before click the switch, i get really bad noise. i will try in a different location/perhaps with a different guitar without single coils, and see if that matters.

-paul

Paul Marossy · August 18, 2006, 09:45:54 PM

Quotei will try in a different location/perhaps with a different guitar without single coils, and see if that matters.

I don't think that there is much else that can be done other than that.

plaiming · August 19, 2006, 09:12:58 PM

well, i played around some more last night. it basically appears that as the wah is toe'd down
the high frequencies are more pronounced - the already present noise is being amplified more and
accentuating it. its very strange cause when the wah is off the noise isnt really that noticable. im wondering
if somehow activating the wah is allowing more noise. like i said, the wah seems to sound pretty decent, a
little more lows/mids and maybe a longer sweep - its seems to sweep very quickly...
im going to play with some other guitars and maybe even compare to another wah cause im pretty new to them.

thanks for all your help! i think this thread has run its course..

-paul

Paul Marossy · August 19, 2006, 09:25:13 PM

Quoteit basically appears that as the wah is toe'd down
the high frequencies are more pronounced - the already present noise is being amplified more and
accentuating it. its very strange cause when the wah is off the noise isnt really that noticable. im wondering
if somehow activating the wah is allowing more noise.

Not really that strange. Your wah pedal is only doing it's job. It does amplify the input signal somewhat. When your pedal is in the toe down position, it's accentuating only the highs within a small frequency band. You're just hearing what your pickups are picking up from the local surroundings, but singled out and amplified. It can work the same way with 60hz hum from motors, compressors, etc.

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Help with vox wah mods