Foxx Guitar Synth Wah

[digi2t]

Here's another rare pedal, the Foxx Guitar Synth (currently 1395$ Buy it Now on Ebay  );





but I've got a question concerning this schematic;



The upper quad opamp, specifically Z2-3 and Z2-4, the opamp "+" inputs, I'm assuming connect to the lug of the 1M sensitivity pot at the input?

I'm just looking for a second opinion, although it makes sense to me, since the rotary selector will either give you band-pass, or low-pass, from the input.

Sorry if the quality of the image is weak, it's the best I can do.

I think I'm going to try another Vocalizer type ressurection here. This should be interesting  .

Cheers,
Dino

[Mark Hammer]

It's a Mutron III with manual sweep.
That's not a criticism, merely an observation.

[digi2t]

Not taken as criticism, but as a directional aide  .

Thanks amigo, time to study the Mutron III schem.

I can't even find a sound clip, let alone a video of this puppy (like the Vocalizer, before I built it). It's got my curiousity peaked.

[digi2t]

It's a Mutron III with manual sweep.

Yup, almost identical. Should be able to fill in any blanks I may face.

Muchos gracias 

[Mark Hammer]

One of the small differences between this and the Mu-Tron is that the Mu-Tron adjusts the signal level hitting the filter and envelope follower via a gain adjustment pot on the first stage.  The Foxx uses a fixed gain on that stage, with an attenuator pot ahead of it.  Same diff, I guess.

As an aside, if you check out the effectsdatabase, you'll see that the basic Mu-Tron circuit was licensed to a LOT of different companies.  I used to have one of the Funky Filter pedals, back in the 70's, that I bought...new....for $25, not realizing that it WAS a Mu-Tron, but thinking it was a cheap imitation.  Perhaps, Mike Biegel licensed the basic circuit to Foxx too.

[digi2t]

Yeah, I've been digging into it today, and you're absolutely correct. I've been spotting this circuit, or variants thereof, can be found in other pedals. If anything, this has been a good "eye-training" exercise.

You know, one thing that's boggling me right now, is the cap on the pot in the picture above. I've been staring at the diagram, and the picture side by side, and I can see where the circuit is going, but I can't seem to spot the cap in the diagram.

I think I've been staring at the forest for so long now, I can't seem to spot the tree. I need a cup of coffee 

I also found on JC Maillet site, that he stuck a Mutron III into a wah as well, using the treadle for the wet/dry control. He also brings up a very good point about using a trimmer on the voltage divider (repalcing the resistors) to fine tune the opamp bias. Interesting...

[Mark Hammer]

You're about 6 weeks late.  He was over at the house when I had the party for Steve Daniels in late October.  Had you either come in to Ottawa, or notified me, we could have brought it up for discussion.

[digi2t]

Here... I'm passing you the salt.... rub it into my wound why don't ya 

I'm going back to looking for my cap (I'm pouting my lips, and connecting my eyebrows) 

[digi2t]

I'm beginnig to think that the cap on the pot is actually the 2.2uF electro shown in the diagram, just above the +9v. Since it either swings to ground, or goes direct to -9v, it isolates the positive side?

I've just never seen an electro cap that looks like that, and I have a layout of the PCB, and there is no 2.2uF cap showing. Maybe that's whats messing with my mind. I'm just having trouble seeing how it works placing it on the pot vis a vis the wiring. 

Screw the coffee, I need a Red Bull...

[Chugs]

Crikey! Trying to read that schematic is giving me a headache!  Interesting though, I like anything that can be built in a wah enclosure.

[Mark Hammer]

I'm surprised we haven't seen any threads about how to produce the faux velour fuzzy finish on Foxx enclosures.

[Ronan]

Dino, the cap on the pot in the photo is known as a "brown turd" in my country, it is not an electro, but a polyester or mylar type cap, of a later vintage than the caps used in that pedal. I'd say it is a "mod" of some kind, who knows. Do you know exactly what is going on with that DPDT switch at the pot, labeled something like "pedal speed + manual or speed"?

[Chugs]

Mark, how about the finish on this pedal?

http://www.ebay.co.uk/itm/ThorpyFX-Clark-Gainster-Clone-Klon-Hoochie-Mamma-overdrive-/110783823254?pt=UK_Guitar_Accessories&hash=item19cb3afd96

[digi2t]

Dino, the cap on the pot in the photo is known as a "brown turd" in my country, it is not an electro, but a polyester or mylar type cap, of a later vintage than the caps used in that pedal. I'd say it is a "mod" of some kind, who knows. Do you know exactly what is going on with that DPDT switch at the pot, labeled something like "pedal speed + manual or speed"?

I was pretty sure that it's some kind of mylar, or metal film, but I was kind of reserving judgement seeing how my experience is rather limited in this field. You folks must have really insulted them with the "brown turd" moniker, I figure that's why they took on colors, and became "tropical fish"?  

That part of the circuit (from what I gather) might control the envelope speed/decay. Either directly, via the pedal (manual?), or by how hard you "strike" the strings (strike?). I reminds me somewhat of the Uglyface sensitivity adjustment in a way. There's also another switch downstream that dictates whether the pedal is simply a wah, or sweeps the envelope. To my untrained eye, the Foxx seems to be using haly of the IC as a CV for the envelope control. As Mark pointed out earlier, this pedal has got "Mutron" written all over it. Maybe this pedal is rare because there was too much going on, or maybe Mutron sued their ass? JC Maillet modded a Mutron III into a wah shell, controlling the decay via the treadle, like this (sorry it's sideways, it's a direct link);


It's just that the Foxx diagram shows a 2.2uF electro cap on the +9v line (going to IC Z1-1 neg. input), which I think acts as a block when we switch the neg input to -9v. I have a layout of the PCB that came with the schematic, and there is no 2.2uF cap shown. Meanwhile, two different gutshots show this "turd" on the pot.





Maybe the schematic was a first draft, and changes were made later in production?

I'm REALLY curious about this one, so it's going on the breadboard this week. I just have a weakness for these rare/obscure/over-priced-on-EBay pedals.  

In the meantime, any trained observations are (as always) most welcome. I love going to bed a little less stupid at night  

*edit*:
I copped this from the EBay ad;
Here's a something really cool! It's a Foxx Guitar Synthesizer I, Model 9. No doubt, it is vintage and rare and incredibly cool, I must inform you (if you are not already aware) that it's not really a synthesizer. It's actually a somewhat complex and sophisticated envelope-controlled, phase shifter/wah pedal. The wah/filter circuit uses a Vactrol, similar to the MXR Phase 100, and the effect can be swept with an LFO or you can use the foot pedal to sweep. Also has high/low sweep and you can change the direction of sweep and the direction of the envelope. You can freeze the sweep and just have the envelope control.

I'm going to email them, and ask if they can send me some pics of the guts. Wish me luck....

[digi2t]

YYYYYEEEEEEEHHHHHHHAAAAAAAWWWWWWW!!!!!!!!!!!!!!!!!!!!!!!! I got the mother working!! If you like Mutron III's, wahs, autowahs, LFO's, and a bit of flanging (kinda), well, you came to the right place. This sucker is a gas. There are some settings that even remind me of my Gristleizer.

Well, the schematic has some major errors in it, so I'm hesitant to believe that it ever came from the factory. In any case, with guidance from Mark Hammer, R.G. Keen, and J.C. Maillet (big FAT thanks guys!), their words of wisdom, and websites, put me on the right path. What we've got here is a Mutron III copy, with an LFO built in. Like the Mutron, it's got the LP/BP/HP filtering, gain control, lo/hi filter, up/down sweep, and so on. Unlike the Mutron, it doesn't have the resonance control, but does offer some psuedo flanging type effect. The resonance control easily added (I have it on the breadboard). The treadle is either a filter sweep control, LFO speed control, or is bypassed in autowah mode.

Ronan, that "brown turd" is the LFO speed range cap. The schem says 2.2uF electro, but you can use different caps to increase/decrease the range. One thing I found though, I am getting some faint ticking bleeding of the LFO into the audio. I'm hopeing that it's because of the lack of shielding, but I'll cross that bridge when I get to it.

OK, here's a video of the sucker on the breadboard. Since I had some VTL5C3's on hand, that's what I'm using. Needless to say, I had to stray from the schematics to compensate for the response of these Vactrols, so lucky for me I had lots of trimmers on hand. I recently ordered some LDR's for the EH Talking Pedal project, and I'm going to try them instead when they get here, since then I'll only need to run one LED. When I do build this, the resonance control, output mix control (thanks J.C.), and maybe a speed range selector for the LFO will go into this. Also, since this pedal requires +9v and -9v, I'm running it on a MAX1044. I'm using two LM324's, leftovers from the Mr. Multi build. They seem to have brought their good mojo with them. Or, maybe the fact that I just got some TL074's in, scared the crap out of them into working well. Who knows...

Here's what I have to date;

Once I get the schematic finalized, I'll whip up a vero for it. Once again, big thanks to all those who chipped in with guidance. I'm soooo glad I took this one on. 

[StephenGiles]

Great stuff, very interesting!

[digi2t]

More fine tuning....

LFO ticking bleed when in envelope mode is fixed. Since you can either be in "pedal" mode, or "envelope" mode, the "pedal/envelope" footswitch will be converted from a SPDT to a DPDT. The line going to feed -9v to the LFO will now detour to the "pedal/envelope" footswitch, and then go back to it's pole on the pedal footswitch.
I had noticed that if I was in "pedal" mode, with the LFO on, if I switched to "envelope" mode, the ticking was bleeding through. Although the pedal is disabled now, that would mean that I would have still have to click the pedal as well to kill the LFO. That's when it dawned on me, I'll give the "pedal/envelope" switch a double duty. Shielding or not, this will ensure quiet operation.
If you switch out of "pedal" mode, then it will also kill any power going to the LFO. After all, it's a moot point having power going there if the treadle is disabled. This way, if you're in "pedal" mode, and switch out to "envelope" mode, you won't get any ticking, and you can simply switch back to where you were before. No double switching.  

I A/B'd the IC's again, and I found the TL074 sound a touch better, and a tiny bit quieter. The LM324's are now sulking in their drawer. On the the Foxx diagram, they show a 20K, and 220K resistor going to ground from pins 10 and 12 of the IC, whereas these pins go to ground on the Mutron. I tried both, and straight to ground is better. Envelope sounds, well, "wonkier" for lack of a better term. Score 1 for the Mutron.

I've got the VTL5C3's tuned to the point where they sound pretty damn good, so I guess I'll keep them. This also means a different resistor/trimmer to ground combo, in this case, a 270 ohm resistor below a 25K trimmer. This combo put me in the right range to dial in the sweet spot for these Vactrols that's useful for all the filter modes. I initial used a 100K direct to ground. I set it to the max 100K, and then started dialing back slowly. The danger here is that you don't have a resistor as a safety to prevent you from hitting ground directly, so be warned. I should have used a 1K, or a 560 ohm at the very least, as a backup, but I winged it this time. When I was satisfied with the sound, I pulled out the trimmer, and it gave me 10K on the meter. I settled on a 270 ohm resistor to ground, with a 25K trimmer on top. It gives me all the range I need.

The UP/DOWN balance was driving me nut for a while, because I was getting a different decay rate between the two. I installed a 250K trimmer as a voltage divider, to balance between the UP and DOWN modes, and I just couldn't find a happy medium between envelope, and LFO mode. I get one down, and the other one would go off. Then I spotted the problem... on the Mutron both resistors on the UP or DOWN poles are 22K. On the Foxx drawing, one is a 12K, and the other a 22K. That's what I breadboarded. When I realized the difference, I replaced the 12K with a 22K, and it made a world of difference. The decay between modes, or LFO mode is really nice now, being fairly even on either side. Funny enough, R.G. "Neutron" also uses the 12K/22K combo, but it just doesn't line up for me  . I'm not quite sure what's going on here, but Hey!, if it works... I see that J.C. used a 330K for the divider, but the 250K is working fine here, besides, I can't find a 330K multi-turn. Either way, score 2 for the Mutron.

Another dilemma is the cap just before the envelope detector. The 10uF is just too much, making the whole thing very bass sensitive. 2.2uF a la Mutron is nice, and I tried J.C.'s 0.1uF idea as well. Both worked well, but for me, a 1.0uF works nice to my ears, especially in high pass mode. This is going to be one of those "season to taste" thingys, to each his/her own. *edit* I tried a bunch of different diodes here as well, germanium, silicon, and LED's, but the best response I got was with 1N4148's. As per R.G. "Neutron" work alike. He shoots, he scores. It was kinda cool though with the LED's. They flash as you play. 

And, in case you're wondering (maybe not, but I'll tell you anyway), the UP/DOWN switch also reverses the sweep on the pedal, if so desired. NOW HOW LOOC IS TAHT!! If you're "wahslexic" (dyslexic using a wah), it can accomodate you as well.

I made another video, this time with all the above mentioned mods. I'm blasting through all the different setting, so you can get a of this thing, in better tune;

I'm going to draw up a new schematic, incorporating all the new tidbits and corrections, and post it in the next few days. Once I try a proper UP/DOWN trimmer (I'm using a pot, not precise enough), then I'll start a vero. IMHO, this is a really cool wah, that never got a fair shake. Maybe Foxx tried something, but didn't want to get bitch-slapped by Mutron, I dunno, but it could be a really great tool on the pedalboard with the right tweaks. As my bro Jimi would say, I'm going to "ressurect it's ass", and make sure it doesn't cost anyone 1400 smackers in the process. I think I'm going to rename this sucker "The Foxxtron", or maybe the "Mufoxx".

Stay tuned.....

[DiscoFreq]

I have one of these that needs some repair... 

I'm surprised we haven't seen any threads about how to produce the faux velour fuzzy finish on Foxx enclosures.

I think it's described in  AnalogMan's Guide To Vintage Effects. It was something electrostatic and there was a high rate of failure, so they had to remove that layer and try again.

[digi2t]

I have one of these that needs some repair... 

What's wrong with it?

[Mark Hammer]

Some time back, at the dawn of recorded history, I made an EPFM-I Super Tone Control and installed it into a wah shell.  The EPFM STC is also a fairly standard variable state filter, like that used in the Mu-Tron and all its cousins, with switch selectable hi/lo/bandpass filters and notch.  I wired it up so that it could be used in wah/anti-wah fashion.  That ended up being particularly useful for the hi-pass setting, where the sound would be thinnest in heel-down, and fullest in toe-down.  There was no envelope control in the one I built, but when EPFM II came out, Craig Anderton recommended using the stand-alone envelope-follower module to auto-sweep the STC.

I guess what this thread needs to do next is generate a standardized mod for Mu-Tron/Neutron/Q-Tron users that will permit foot control, and over-ride the envelope control.