Foxx Select-a-fuzz.

[digi2t]

Seeing as there are only two trace side gut shots, and no one is willing to post components, I took some time to look at this.





The pictures seem clear enough to make out what might be a resistor, or a cap. Cap polarities are fairly clear as well. Even a diode symbol can be made out. Wire connections to the board seem to be bigger solder blobs. Transistor E and C letters are there. So looking at, I get this;



Two things that pop out at me, are the resistor/cap in series between B and C on Q2. Never seen that before. The Sustain pot set up is a new one for me as well. At least, the way I see it from the pictures it is.

Anyone interested in flinging some component values at me? I'm game to throw this on the breadboard and play with it.

[Gus]

This could be fun to figure out

I would guess it might be the same transistors used in other Foxx effects
The one picture shows an B10K  sustain control

The resistor cap reminds me of the big cheese schematic.   

It is hard for me to read the marks on the PCBs with my monitor to check your work

[TGP39]

These were the only other pictures I could find. Sorry, it's not much help.

Steve.

[Luke51411]

I think the purple fuzz is part of the secret, it's come alive and is growing inside the box. I hope you can get this sorted for preservation sake. Too bad no one will open it up for us but what challenge would that be?

[Arcane Analog]

I took a stab at cloning this a while back. One of my many started and forgotten projects. I will see if I can find my notes.

[digi2t]

Thanks for the pics Steve, they help validate some of what I thought I was seeing.

I won't be able to breadboard this until Sunday, but if someone could explain the sustain set up, I'd appreciate it. Looks kinda like a tone control to my noob eyes.

[digi2t]

Hey Gus, this is what I see. Hope it helps you;

[Rob Strand]

I did a quick scan.  I can see two errors:

- R9 goes from the base of Q3 to ground, not to the -ve side of the cap
   (ie. Q3 has a standard feedback + divider bias).

- There is a resistor missing R5 and the connection to resistors R6 and R11 needs to be fixed as follows:
- +9V to one sideof  R5
-  the other side of R5 forks off to R6 and R11 (no other connections at the fork point)
     the other side of R6 goes to the collector of Q2 (and R2 etc)
     the other side of R11 goes to the collector of Q3

The sustain pot is 10k linear.
The volume pot is probably 50k

[Added]
The wiper of the sustain pot goes to the base of Q3; interestingly that changes the bias of Q3
I think the Fuzz switch labels are reversed.  Heavy fuzz is on the electrocap


I've updated the schematic including the designators but I don't have an account to post it.

[digi2t]

I did a quick scan.  I can see two errors:

- R9 goes from the base of Q3 to ground, not to the -ve side of the cap
   (ie. Q3 has a standard feedback + divider bias).

- There is a resistor missing R5 and the connection to resistors R6 and R11 needs to be fixed as follows:
- +9V to one sideof  R5
-  the other side of R5 forks off to R6 and R11 (no other connections at the fork point)
     the other side of R6 goes to the collector of Q2 (and R2 etc)
     the other side of R11 goes to the collector of Q3

The sustain pot is 10k linear.
The volume pot is probably 50k

[Added]
The wiper of the sustain pot goes to the base of Q3; interestingly that changes the bias of Q3
I think the Fuzz switch labels are reversed.  Heavy fuzz is on the electrocap


I've updated the schematic including the designators but I don't have an account to post it.

All duly noted, and here is the updated schematic;



Guess I should have gotten more sleep before drawing 8-P. I've added the designators. The look over is greatly appreciated Rob. Thanks.

[Rob Strand]

Looks good digi2t!

[Gus]

First stage looks like a FF type with added C to B cap and C to B cap and series resistor

So I would GUESS
R3 of 47k to 100k  bias feedback
R4 2.2K
R1 10k to 47K
R6 8.2K and up
R5 has both stages coupled HOWEVER there is no bypass cap at the R5,R6 node and no cap at the battery +9 so maybe it a feedback mix thur the power supply
C8 1uf and up

I could keep guessing but without more information on the parts it is only a guess AND with circuits like this every resistor and cap value selected will change the sound

Output stage is the type bias you find in a BMP input stage without an emitter resistor HOWEVER as Rob Strand posted the sustain also changes the last stage bias

EDIT did a DC sim for operation points and sent it to digi2t
This might be a fun circuit

[Rob Strand]

I think it is safe to say the transistors are silicon.  It is not clear if they are high gain or low gain types.   

The diode type Si vs Ge is not obvious.

C6  150 to 220p would be a good start for a proto

C7, R2 and and C10 are hard to guess.  So too is the biasing around Q3.
However,  I suggest listing to the sound sample on youtube.  It sounds like Q3 could be biased close to cut-off.  It shouldn't be hard to tweak the biasing to get that sound.

[armdnrdy]

Did you see this Dino?

http://www.musicparts.com/products.asp?Company=Foxx

Nick Bungus and I separately tried to contact the proprietor of this site to see if he could "ready" the offline Foxx Phaser pedal schematic.
Nick's request was answered but still no schematic posted. I have yet to hear from him after two emails.
The select-a-fuzz schematic is listed as "offline" but you might try to contact him. You might have better luck than we did.
There is also a phone number with the suggestion to call if you do not get a reply by email.

[Gus]

I listened to the two Videos linked at http://www.effectsdatabase.com/model/foxx/selectafuzz
The fuzz seems to be tuned more to the bass side.  Makes sense with the FF like stage with C to B caps and the lowpass part of the tone control.
The videos did not have the sustain changed, one changed the input caps
anyone know of a video sound sample with the sustain control being used?

A GUESS for the range of input caps 10uf, 1uf, .1uf .047uf .01uf hard to tell from the recording

It sounds like a Si fuzz with lowpass filtering( C6, C7 R2, C10) and an edge added from the operation points of the transistor(s).  Rob Strand posted about the biasing and a starting point for the FF stage caps.

I sent digi2t a DC sim and some GUESSES for part values HOWEVER being a fuzz you can bias "wrong" and get a sound and my guesses could be off. 
EDIT
I was changing values in the sim even if it is not a clone this could be a fun base to build another fuzz

[digi2t]

Did you see this Dino?

http://www.musicparts.com/products.asp?Company=Foxx

Nick Bungus and I separately tried to contact the proprietor of this site to see if he could "ready" the offline Foxx Phaser pedal schematic.
Nick's request was answered but still no schematic posted. I have yet to hear from him after two emails.
The select-a-fuzz schematic is listed as "offline" but you might try to contact him. You might have better luck than we did.
There is also a phone number with the suggestion to call if you do not get a reply by email.

Like I mentioned in my first post, this sucker has been on the perifiery of my mind for a while. I did contact musicparts about two years ago, but the the response was that it wasn't available (no reason supplied). Maybe they simply compiled a manufacturers list, and put online what they have.

I listened to the two Videos linked at http://www.effectsdatabase.com/model/foxx/selectafuzz
The fuzz seems to be tuned more to the bass side.  Makes sense with the FF like stage with C to B caps and the lowpass part of the tone control.
The videos did not have the sustain changed, one changed the input caps
anyone know of a video sound sample with the sustain control being used?

A GUESS for the range of input caps 10uf, 1uf, .1uf .047uf .01uf hard to tell from the recording

It sounds like a Si fuzz with lowpass filtering( C6, C7 R2, C10) and an edge added from the operation points of the transistor(s).  Rob Strand posted about the biasing and a starting point for the FF stage caps.

I sent digi2t a DC sim and some GUESSES for part values HOWEVER being a fuzz you can bias "wrong" and get a sound and my guesses could be off. 
EDIT
I was changing values in the sim even if it is not a clone this could be a fun base to build another fuzz

Crap! I hadn't noticed this video;

He switches through the whole range of caps, but I think the Sustain is pegged. These must be the only two videos around.

As for the cap choices, that's definately a good starting point, but there's one angle though; of the five caps loaded on the board, only one (heavy fuzz) seems to have the +/- marked on the board. That leads me to believe that there might only be one electro on there. At least now, with the video mentioned above, I have a better idea of what to aim for.

Anywho, got some deck work to do today, but I'm retiring to the breadboard tonight to experiment with this. This is going to be sweet!

[Gus]

I noted the electro +- marking but I did not think 70's I was thinking a 1uf film. So maybe a .47uf film etc.
Sounds like heavy filtering maybe C10 is something like a .1uf with the values I sent
I sent values that should move Q3 closer to cutoff like Rob Strand posted.  I would adjust the bias feedback resistor maybe make R10 a 100k with a 1 meg rheostat for a 100K to 1.1meg to find the value

[Rob Strand]

I noted the electro +- marking but I did not think 70's I was thinking a 1uf film. So maybe a .47uf film etc.
Sounds like heavy filtering maybe C10 is something like a .1uf with the values I sent

The size and the fact it is only 100V makes me think C10 is 470n (0.47uF).  But the circuit function makes me things it's less like 100n or 220n.

The other thing to notice is, either C1 or C2 (ie. near the cap-switch) looks about the same size.   Perhaps C1=100n and C2=470n?  or is it C1=470nF.  Hard to tell.

[digi2t]

My money is on 100n. Zooming in, it looks like the top of a "1" peeking out from behind the wire. Like it would say "0.1 M" or something.

As for the other jelly bean, hard to say without knowing the voltage, but for production purposes, yeah, could be another 100n as well.

Anyway, so far, I'm getting some pretty gnarly fuzz on the breadboard. I just need to play with some values some more to tame it, and get the sustain pot to be more effective. It's looking (sounding) promising right now.

[armdnrdy]

Dino,

I just got off the phone with the guy from MusicParts.
I requested an offline schematic for the Foxx Foot Phaser.
While I had his attention...I asked him if he could pull and "ready" the Foxx Select-A-Fuzz schematic as well.
He said that it might take about a week. Hopefully, my phone call lit a fire under his rear and prods him to get these drawings loaded up on his sight!

[digi2t]

Dino,

I just got off the phone with the guy from MusicParts.
I requested an offline schematic for the Foxx Foot Phaser.
While I had his attention...I asked him if he could pull and "ready" the Foxx Select-A-Fuzz schematic as well.
He said that it might take about a week. Hopefully, my phone call lit a fire under his rear and prods him to get these drawings loaded up on his sight!

Larry... super kind of you to pass that on.  Every little bit helps. A tip of the hat to you brother!