freestompboxes.org

Snagged these off TGP.

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Very cool.

Any idea of the transistor type ? looks a bit like BC108/109 ...
From the picture it seems it has an output buffer but no input buffer ?

2 diodes ??? I can imagine (what seems to be) a 1N4001 for reverse polarity protection. But what's the Ge diode for ? Then again, they're close to the output buffer ... so clipping maybe ?

OK I'm game

Controls are sweep, mids, growl and volume.

Referring to the Geofex nomenclature :
Sweep is definitely Rw (100k ?)
Mids is probably replacing the 1.5k Rfb resistor
Growl : not sure but my money goes on Re1. Wilson site says it increases gain and bass, and that's what Re1 does.
Volume : I'm still scratching my head on this one : The typical wah circuit delivers less than unity gain.
If there's a volume pot, there must be some additional gain somewhere. I see only 3 possibilities :
- maximum Re1 value is lower than 470R. I doubt, this does increase bass response and clipping but not any meaningful gain at the wah output (verified with Spice).
- Rin lower than standard 68k. And I'm pretty sure it is.
- Q3 is not setup as unity gain outbut buffer but rather as a fixed gain booster or something. I have my doubts here as well.

My guess is thus a low Rin value and Q3 set up as buffer with a volume knob (voltage divider) right behind. Just like the McCoy wah buffer from Fuzzcentral. But I might be wrong of course ...

It is interesting to note that this wah would then not have a "Q" pot, referring to the 33k Rq resistor.
It seems Mr. Wilson decided to leave a fixed resistor here. Again, just a wild guess as the mids control might refer to Rq instead of Rfb after all ...

Anyone has an idea of the purpose of both 47pF caps ? To smooth Q1 and Q2 response ?
Is that really a Ge diode I see there ?
I can identify a couple resistors but is there anyone with better eyes ?
I'm totally at a loss with the capacitors type/values. What is a "1, J" cap for instance ?

I think I've got most of it now (and plenty errors in my previous posts).

The circuit is a copy of the Vox McCoy wah with output buffer just as in the Fuzzcentral schematic but with a couple changes :
- The volume pot is not a voltage divider after the output buffer. It has only 2 lugs connected and it actually replaces the 68k input resistor. Looking at the videos, 3 o'clock seems to give unity gain which is said to sit around 50k, so my wild guess is a 200kA pot.
- The mids pot replaces the 1.5k feedback resistor. My guess is 5kA
- Growl pot replaces the 470R resistor @ Q1e, probably 1kA
- The vertical resistor (bottom left in pic) is the one in parallel with the inductor often referred to as "Q" resistor. 33k in the original wah, 100k in the McCoy. I cannot read the bands but I assume it's 100k here as well. In any case, the circuit has a fixed Q.
- The circuit has an additional 1M pulldown resistor at its input
- The power regulation is the one found in current GCB95 productions : 100R in series, 1N4001 to ground for reverse polarity protection + 1 Zener diode (I suppose 9.1V) to ground for overload protection.
- The circuit includes a LED + 1k resistor.
- 3PDT switch wired for true/hard bypass with circuit input grounded when bypassed
- The only possible implementation I can come up with for both 47pF NPO caps is to place them between collector and base of Q1 and Q2 (radio frequencies ?).

I still don't understand how the expression pedal is connected. You'd need to switch 2x2 terminals for it to work (otherwise it leaves part of either resistor in the circuit) but AFAIK a stereo jack only permits to switch a single connection ...