Vox wah wah mods

[Spencerleehorton]

Here are a couple of the pcbs with the trimmers but only two electrolytic on both pcbs?

 

[Spencerleehorton]

From that schematic it looks like the 100k can be trimmers as well as the 470ohm, the other I think would be the 68k on input which can be lowered for more volume I think?
470 ohm would change the bias of Q1?
Not sure about the 100ks but I think they would be Q of curve and gain?

• • Trimpots for adjustment of Q, Bass/Gain, Mids and Volume

From the picture there are 8 resistors and 4 trimmers, on the Clyde circuit only 10 resistors, so possibly some smaller resistors to stop the trimmers bottoming out?

 

[dai h.]

(from what I recall apparently happened) Geoffrey Teese sent Stewart a kit (Teese used to sell drop in RMC3 kits), then later Stewart came out with his own (without the variable 10nF connected to the second transistor).

IIRC one trimmer was for the 68k at the input, another to vary the 1k5, another for the R in parallel with the inductor, plus another paralleled with the 4u(-ish) cap with one end of the cap connected to the wiper (not totally sure if I'm recalling correctly).

Teese used to goop the caps connected to the DIP switch in earlier units (but not in later--so I doubt I'm revealing some super secret here--you can find pictures on the web). They were axial ceramics with values of 240p (two 120p), 470p, 820p, 1n5, 2n2, 4n7, 10n, 22n, and 47n (plus two trim caps (100p?). From what I gathered they didn't need to be that exacting in tolerance. (If anyone tries putting in rotary switch or whatever to play with that 10nF value I very strongly recommend adding pop suppression Rs because hearing the pop when going direct is seriously brutal on your ears.)

This page used to be up on the Teese site and the tunings (not all) seemed to be based on a 20% tol. 10nF though maybe pointing out the obvious) :

https://web.archive.org/web/20060908041215/www.realmccoycustom.com/RMC3TUNING.htm

Oh, also the other alu electro is probably for a power supply filter--they seem to be (something like) 1k(-ish) plus 100u or 220u.

Also, (reading some of the comments by Gus, RM, etc.) seems like a bit of a crapshoot unless things were selected or tweaked esp. for the mass-produced ones.

(dang blasted leaking memory cells...) yes that 470R for Q1 is varied in (Fulltone?) I vaguely recall fixed R in parallel with a trim pot. So another parameter to play with.

 

[CJ]

we got a Slash cry baby in the store, dont know what thats all about, maybe he ripped it from S.I.R ?

 

[Spencerleehorton]

i am tackling this pedal on my other thread

Fuzz face clone with bias control

might want to repost on there and then i can clean up this thread a bit?

 

[Spencerleehorton]

well ive redrawn out the original wah pcb from the picture of Jimis wah, all components seem to match apart from the 4uf non polar cap is 10uf non polar and the extra 1k resistor on output.
the only other cap which isnt confirmed is the one cap on the underside, i think its another 10nf but would like to confirm this? ive tried 12nf in parallel with the 10nf and it sounds pretty close to what i think it should sound like.
The other thing i noticed some schematics draw the 68k after the first 10nf but the original jimi wah has 68k first then the 10nf.

 

[Potato Cakes]

When I modded my Vox wah pedal, I went through a number of pots to get the frequency to be more evenly distributed over the sweep of the rotation. I wound up with the 200k version of this:

https://fulltone.myshopify.com/products/fulltone-wah-pot-fwp-1-fwp-2?variant=31402044227689

They have been out of stock for some time and I paid more for one used, but it now doesn't have that jump in the high frequencies that I found to be unpleasant when feeding a distortion pedal that I had experienced with several 100k pots from respected manufacturers that were specifically designed for wah pedals.

Thanks!

Paul

 

[dai h.]

Dave Weyer said it was a 3n ceramic:

https://forum.metropoulos.net/viewtopic.php?f=33&t=45063&start=240#p463043

IME (unless it was selected) it probably didn't measure really close to 3n.

FWIW, there is some controversy re: the pedal. One thing I noticed myself is that the serial no. was listed on the auction as "1855698", and according to Vox Showroom:

http://www.voxshowroom.com/us/misc/crybaby.html

adding 57 to the first two digits gives the year, so (assuming that is correct), (the bottom plate at the least) dates to 1975...

Also, according to this wah article on the analogman site:

https://www.analogman.com/kraft.htm

"TDK (inductor) was introduced in roughly 1968"

Additionally, I found some notes on some black Dunlop inductors (with "D" logo (and epoxied inside?)) I measured years ago:

(1kHz)
1) 624.9mH 15.5 ohms DC
2) 644.4mH 18.0 ohms DC
3) 646.7mH 16.5 ohms DC
4) 648.0mH 16.5 ohms DC
5) 712.0mH 14.8 ohms DC

(hmm... that last one looks a bit strange)

 

[Spencerleehorton]

ah all good stuff, also i didnt realise that those caps were not polystyrene, they are Paktron film caps!!!
ive used some polystyrene and mine sounds pretty good but ordered some tropical fish and will try an array of others.
thanks for that info for the ceramic 3nf, i'll try it.

 

[Spencerleehorton]

Put in the trimmers and used 12nf + 1.6nf underneath pcb to get about 14nf on first 10nf cap.
Changed transistors to bc 109B.
Plugged it in and powered it up and all I get is hiss when I rock the pedal forward!!
Must be a cold solder joint!!!

 

[dai h.]

some wah threads@aron's stompbox forum:

https://www.diystompboxes.com/smfforum/index.php?topic=84996.0
https://www.diystompboxes.com/smfforum/index.php?topic=109929.0
https://www.diystompboxes.com/smfforum/index.php?topic=88660.0
https://www.diystompboxes.com/smfforum/index.php?topic=77870.0
https://www.diystompboxes.com/smfforum/index.php?topic=79569.0
https://www.diystompboxes.com/smfforum/index.php?topic=88277.0
https://www.diystompboxes.com/smfforum/index.php?topic=96347.0

some Youtube vids on rolling your own inductor:




couple places selling inductor kits (Banzai and Small Bear I've heard of (SB has been around for a while now, the other one (which I haven't heard of before) is less expensive but doesn't come with magnet wire) :

https://www.banzaimusic.com/Wah-Inductor-Kit-Epcos-N48-Material.html
https://smallbear-electronics.mybigcommerce.com/wah-inductor-kit/

http://uk-electronic.de/onlineshop/product_info.php?products_id=1122&language=en

Lastly my RM kit inductor was 1003 turns (850 and 153 (it had a tap which gave a thinner sound--wasn't really sure how useful that was although interesting)).

 

[Spencerleehorton]

Well bit of a head scratcher at the moment as I’ve put in the trimmers and set them at the values that were in there, changed the transistors for bc109B and no longer get a wah sound just a very flat sounding tone control?

 

[Spencerleehorton]

Going to make a few pcbs, a copy of the vox and I’m going to do a original layout version and attempt one with the trimmers in.

 

[dai h.]

Well bit of a head scratcher at the moment as I’ve put in the trimmers and set them at the values that were in there, changed the transistors for bc109B and no longer get a wah sound just a very flat sounding tone control?

sorry, my knowledge isn't zero but I'm no tech so can only suggest the mundane. Solder joints good? Open or missed connections? Pin-outs not something odd for the transistors?

As far as my own (crude) experimentation with the trim pots, sockets, cap value changes I don't remember having particular issues and it seemed straightforward, save for one when trying a variable pot for the Q1 emitter R (as on (some?) Fulltones. When I tried a chassis-mounted pot, had some weird instability (C across the emitter R doing something or the grounding?). Also, (not to do with trim pots) had scratchiness with the pot which turned out to be a bad solder joint (ruined a Fulltone wah pot chasing this by using Cramolin--they did advise in a comment or website not to do this IIRC). Additionally, if you use sockets for experimentation, with repeated insertion/removal, the contacts can come loose over time and not make good contact (had some hair-pulling frustration chasing this in a Tube Screamer copy once).

edit: noticed you're using multi-turn trim pots instead of single-turn, so wondered if that could some issue with parasitics(?). Would also seem quite laborious and hard to "find the target" ("set trim pot A to 1 O'clock, etc.").

Also, remembered a thread with very interesting comments about the old wahs from Geoffrey Teese:

https://www.diystompboxes.com/smfforum/index.php?topic=56711.20

This might be good reading for some perspective:

http://www.diyguitarist.net/DIYStompboxes/WahFAQ.htm

Lastly, a factory Thomas Organ pot replacement/adjustment doc:

 

[dai h.]

I remembered this thread at M.E.F. (formerly ampage bbs)--this is really excellent. Highly recommended! :

https://music-electronics-forum.com...t-some-circuit-analysis-and-measuring-results

 

[Spencerleehorton]

Yeah I’m gonna take out the trimmers and put the resistors back in and check it tonight

 

[Spencerleehorton]

Well the pcb was faulty, never mind with that one, Ive bodged it back together where it wasn’t making contact but I’m going to make an original style pcb.
I’ve got BC109B at 350hfe, gonna re wind my own halo inductor using 0.1mm, 460 turns, 30ohms, 500mH.
Polystyrene 10nf, lcar 100k pot.
Have for NP 10uf and 4.7uf will try both probably won’t make any difference.
I tried a 100k pot of the 33k resistor in parallel to inductor and it made a little difference but not a huge difference, below about 10k everything goes muffled, above 10k everything springs to life, this maybe improve when I add trimmers to the other places.
I now have one vox wah which sounds good with halo inductor at 550mH but it about 70ohms, so I’m going to leave this one for the movement as my bench mark and the other vox wah will be the test subject with trimmer and the 3rd wah will be the fully tweaked wah.

 

[dai h.]

re: the inductor, they seem to need some sort of mechanical damping. My RM kit inductor had some rubbery stuff on it, and I guess the dark grey stuff in the Dunlop Fasel must be for that (and to fix it to the casing).

Saw this which was a bit interesting (guy obvisouly into Hendrix playing a lefty Strat upside down):



one thing (not to do with wah) was that he had to unhook his (middle?) tone control for practical reasons (kept hitting it). Then here:

https://www.musicradar.com/news/fx-...-wah-wah-but-making-it-talk-is-something-else

Roger Mayer says, "sometimes I disconnected the tone pots, because it makes the guitar sound a bit more transparent and brighter". So wondered if was just out of annoyance or also for tone reasons.

Anyway, the guy in the vid (Sam Simmonds) uses a wah (apparently made by someone in UK) who seems to have found a bunch of old stock inductor cores and parts:

https://www.facebook.com/venuswitchwah/photos_by

They look pretty pricey though. 80 pounds just for a wah inductor(!).

https://reverb.com/item/74426066-venus-witch-inductor-occult-wah-tone-repro-clyde-mccoy-halo

couple videos on his facebook where you can hear some of his wahs:

 

[Spencerleehorton]

I still would like to know the secret to get the wah working correctly before the fuzz face!!

 

[Spencerleehorton]

this is probably the best sounding wah ive heard on here, definetly getting close to this, so im on the right track.