The ´Zoid Face a.k.a. Schizoid Face
An enhancement of a pinkjimiphoton designed versatile silicon fuzz face

last update: Feb 6, 2020

Copyright 2020 by H. Gragger. All Rights Reserved. All information provided herein is destined for educational and D.I.Y. purposes only. Commercial re-sale, distribution or usage of artwork without explicit written permission of the author is strictly prohibited. The original units  with their associated  trade-names are subject to the copyright of the individual copyright owner. The Author is by no means affiliated with any of those companies. References to trade names are made for educational purposes only. By reading the information provided here you agree to the Terms of Use.
MAIN PAGE>MUSIC STUFF>ZOID FACE

Index

Abstract
Circuit Details
Verdict
Sound Samples
Reference

´Zoid stomp box
The ´Zoid Face (click to enlarge).

A silicon fuzz face (hereafter: FF) following an original design by PinkJimiPhoton[1].

As different to the early designs that use germanium transistors, it uses silicon. The core circuit has been tuned by PinkJimiPhoton to achieve better noise performance and stability over their ancestors while retaining similar tone and distortion behavior - where he succeeded in my humble opinion.

Being a two-face (pun intended) unit (hence the term "schizoid"), it has a laughing and a sour face on the front, whose eyes flash up dependent on the selected mode. I named them "Jekyll and Hide" reflecting a stringent (incidentally: more modern) and a bodacious, evil (more classic FF) mode. Red indicates bypass mode.

I added a few other tricks from my pocket besides input buffering to circumvent all sorts of sound degrading and impedance issues usually associated with such devices.

The prototype. Sadly, a self made PCB´s plus hand wiring is in the light of today´s professional appeal almost deemed a bit amateurish. But this is tweakable, reliable and unique. A commercial PCB is none of that. It was professionals who built the Titanic, but it was amateurs that built Noah´s Ark.

Abstract

I was traversing the web
and stumbled over Brother Photon´s works[1]. I was intrigued by the schizoid face, which is a  fuzz face with two modes (a polished one and an evil one) and got in contact, since recently they blur the images on D.I.Y. forae.
After building some GE devices that come wrapped with some inevitable hiss, I set out to build this one.

From past experience I know fuzzes are sensitive to driving impedance as shown
in one of my earlier articles, it makes the guitar´s volume knob behave differently and makes the FF sound different. Not enough with that, the guitar signal is loaded down and loses clarity progressively. A buffer, which is normally called for rescue, is said to make the FF sound hard, but without, some other pedals will simply not interface with a stock FF.

It is not true that the FF interacts with the volume control on the guitar, in a way that, say, a high capacity cable may form a resonance circuit together with the pickup when the volume is fully up.
  • True is, that the volume pot´s law (and thus its smooth and even volume reduction functionality) get´s altered by seeing a heavy load (faster volume decrease per rotational angle).
  • Also true is, that the FF´s input is current driven, which if driven by a much smaller impedance than a pickup would represent, sounds different.
  • Also true is, that the signal loses treble when the volume is dimed, but this has nothing to do with this circuit.
I personally like to eliminate imponderabilia like those wherever I can. I am sure Hendrix would have done so, if just the technical aspects were as known and mature as they are today.

So I like to buffer my faces. Fortunately, this is straight engineering applied. Even more fortunate, it is easy.
It turns out that this FF unit, GE or not, sounds and behaves much like old GE units you can hear on the internet.

Copyright Notice:
The circuits and concepts depicted here, particularly the artwork, are the sole intellectual property of persons known as PinkJimiPhoton (hereafter: PJP) and Aquataur Music. They are destined for personal use and for educational purposes. Any commercial exploitation thereof is thus at least immoral. Any re-hosting is prohibited.

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Circuit Details

input
                            buffer
Buffer (click to enlarge): the input buffer is a straight copy from a Joe Gagan pedal, which is by itself a straightforward emitter follower. Any buffer would do by the way.

Now, as I explained
elsewhere, a fuzz face does not like to be driven with a low impedance. We talk about a few hundred ohms or even less. Fortunately, a 10k resistance or thereabouts in series with the buffer will yield exactly the same drive conditions as a typical pickup will exhibit. On the board, I have provided a jumper that connects either the raw or the buffered signal to the FF´s input for quick A/B checks, but did not even bother using it since it sounded great from the start.


Input bandwith: I added the ubiquitous anti-pop resistor in front and a low pass filter that kills any RF interference. The signal bandwidth into a electronic device should always be restricted to the bandwidth of interest. Any pedal should have that and you would be surprised, how many designers of commercial units oversee this, for the sake of saving ... almost nothing worth the mention. Hendrix went mad over this during a concert, but what has changed over the decades?

Transistor choice: from my axis face silicon project I had some PN2369A transistors left over (hfe=60), that appeared to work best in pos1. For pos.2 a 2N2222  was lying around (hfe=190) which turned out to work great. Some other, lower gain type, appeared more trebly and less smooth. This is really a matter of trying, but as explained on Fuzzcentral and in R.G. Keen´s Technology of the Fuzz Face, the magic lies in the gain factors. Even a medium power transistor like BD139/140 does work, those have lower gain.

I used a b-c cap of 22pF (Styroflex), 47pF appeared to big. The bias pot appears to settle at 3.5kOhm for greatest clarity.

Bias Emitter Resistors: I fiddled around with these, and ended pretty much with slightly different values for the hfe values chosen. This resulted in a value of 120 Ohms for the first stage and 82 Ohms for the second stage. For the collector, PJP recommends the following biasing procedure:



"(...) [using a buffer] in this case, its [the FF circuit] preset to stay fairly sweet, but i agree, won't necessarily clean up completely. if ya wanna do that, what i do is replace the c resistor on q2 with a b10k trimmer, then turn the guitar down to where it just kicks in, maybe around 1 on the guitar knob... then adjust the bias for the "cleanest" sound i can get. usually that gets you a nice overdrive around 4 or 5 and crank it right up to its full fuzzy goodness."

-Pink Jimi Photon: on freestompboxes.org [2]

power supply
                            detail
LED Supply (click to enlarge):

I tapped the LED´s supply after the polarity protection diode. Very many designs supply the annunciation LED(s) right off the battery, which in case of an accidentally reversed supply polarity may mean the death of the LED. Take into account that some LEDs, such as the RGB types I used, can only withstand reverse voltages up to 5Volts!

Supply filtering: I also made R/C filters akin to valve amps, decoupling subsequent stages. I learned this trick with guitar poppa, this is cheap but optional.

bypass
                          detail
Bypass:  (click to enlarge):

A stock true bypass switching scheme (as depicted and used) grounds the board´s input during bypass to stop noise buildup on the output that may corrode the bypassed signal (red arrow).

Note that PJP originally deviated from this, because he used the switches´ pin to activate the red LED´s during stand by, which is reverse to what may be customary, but eminently valid as an artistic expression. It looks way cool.


led
                          switching detail
LED face frontplate:  (click to enlarge):

The pin that during "effect on"  provides a ground line to the LED(s) (signal ENA, short for enable), is fed to the second switch (Photon Face / Stupid Face as he called it), which in turn powers the green LEDs resp. the blue LEDs selectively.

Since at any time during "effect on" one of these lines is low (both high in bypass) it was obvious to make a diode-wired or type circuit to drive a transistor that illuminates the red LEDs in this case. Voilá, full bypass is restored.

Input Capacitors: I found that in both modes, even with single coils, the input caps are fairly big, i.e. the low end content too big, which does lead to the typical FF mushy low end. While this may well be wanted in some situations, I found myself permanently twiddling the bass cut on the guitar when switching between the modes.

It might thus be a good idea to make the big capacitor (Photon Fuzz side, what I call the evil and bodacious Mr. Hide side) slightly smaller (I used 2.2 µF) and the Stupid Fuzz side (what I call the anally retentive Dr. Jekyll side) smaller by, say, half.
I originally had a 3.3 µF electrolytic capacitor in the first position, but it turned out that due to the buffer in front (and a signal with a DC offset on it) the right polarity could not be guaranteed, so I replaced this with a non polarized cap.

Levels: when switching between the faces, some output level difference is noticeable. This may be useful or be remedied in the future, time will tell.

Pots: PJP suggests a type A pot for the Fuzz control (log), however most commercial units use a type C (antilog). I installed this and it spreads the  usable adjustment range nicely apart. The output pot is type A.

LED annunciation: it appears that upon switching a fairly loud pop is audible, which disappears if the LEDs are removed. This is a clear sign for LED inrush current creating a current surge that is picked up by the circuit. This is a common problem and is exaggerated by the fact that several LEDs are switched at the same time.
I soldered 2µ2 capacitors (non polarized) across the control lines between red and blue resp. red and green. This efficiently slows down the current peaks to make switching pops bearable.

TB MK-II switch: (later addon)

By chance I found out that bridging the buffer´s drive resistance, catapults us into Tonebender Mk-II territory. This differs from a FF by an amplification stage preceding it. Looking at the schematic, this has a drive impedance of 10k, albeit with some gain. Since the buffer´s series resistance forms a voltage devider with the FF´s input impedance (approx. 2k), bridging this yields a gain up step of about 6. Definitely into Mk-II territory. Great sound as demonstrated in the sound section. This eminently justifies the addition of an unobtrusive little switch on the side.

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Verdict

Due to the lack of a genuine GE FF I compared two devices with the ´Zoid face
  • Axis Face Silicon (an all silicon FF that claims to sound like GE)
  • Tarpit Meltdown by Joe Gagan (Nine Volt Nirvana), which I built earlier (yet to be documented). This is a hybrid FF at its heart, with a GE transistor in pos. 2.
  • Brontoboost (NVN too, GE rangemaster type)

All three FFs can´t deny their common heritage and are obviously in the same ballpark, with the Axis Face Silicon being a bit colored. The ´Zoid Face however is very flexible and sounds totally uncolored. An extension of the guitar. I´ll demonstrate that in the sound samples. It cleans up reasonably well, maybe faster than the GE type and has very many nuances of timbre you can adjust with the guitar volume.

The Brontoboost is different since it is built on a different basis. So GE alone is not all. It is the FF dirty goodness.

First, if you are using any FF type circuit, a bass cut facility on the guitar is strongly recommended. This is not stock on most guitars, but very helpful for overdriven sounds. It helps to dramatically clean up distorted tones. Low end gets in the way of the bass guitar anyway.

Secondly, never run a FF into a clean amp. It will sound brittle and awful. Try it. Either you push your amp over the proverbial onset of clipping through sheer volume, or put a mild, tone-shaping overdrive of your choice after the FF, which emulates exactly this. The overdrive, as insignificant as this may be,  does somthing beneficial to tone. For the following sound samples I use exactly that.

So bear in mind, any recording you hear on the web, always reflects the whole sound chain, which is where of course those guys are cheating you. There is nothing constant and thus comparable.


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Sound Samples

The recordings have been done using the following setup and no further processing:

  • Strat with Bill Lawrence (Wilde Pickups) microcoils, neck pickup
  • J-FET buffer directly after the guitar
  • ´Zoid Face :-)-:     Max volume (when guit= full) is set slightly louder, so that the following stage(s) get thumped.
    Equal loudness will be met when guit vol = dimed and FF cleared out. Just like in real life situations. Fuzz control= 12
  • Peavey Bandit 112 silver stripe, clean channel, Resonance on, T-Dynamics fully down, volume=9, all others=12
  • Wampler Euphoria Overdrive, setting = natural. Gain = 1. Slight crunch appears when guit. vol = full and heavy playing.
  • Rode M3 mic @ 20cm distance
  • Recording device: Focusrite PC interface into DAW
(Names may be copyrighted by the associated copyright holder, no association with any of them)

A feq quick and nasty takes. No exercise in timing or else. Crank you speakers.

clean guitar into clean amp, (after pause) with overdrive at the onset of crunch. Hardly any mangling by the overdrive, yet it is felt. Guitar volume = full.


 
stupid face (blue- Jekyll side) :-( , volume at 15 o´clock (18 being max), note long clean decay. Cleans up well.



as above, volume at 17, last measures full throttle.



photon face (green- Hide side) :-) , full volume, second half with bass cut on the guitar.


  • (...)
  • ´Zoid Face :-)-:   (...)
  • no overdrive
  • Peavey Bandit 112 (...),  all controls=12 (loud!)
  • (...)
crazy jimi jam on the photon face (green- Hide side) :-) , riding the volume, slight bass cut.
Note the way the amp gets fatter when the loudness increases. This is straight into the amp without sound shaping overdrives.




A few tests regarding buffered / unbuffered and an alleged similarity with Tonebenders MK2:
(...)
  • Buffering as specified
  • Clean Boost as specified
  • ´Zoid Face :-)-:   Stupid face = Jekyll face, all other settings as above.
  • Peavey Bandit (...),  volume=9, all others=12
  • Wampler Euphoria Overdrive (...)
  • (...)
FF stock (no buffers). Guitar= full volume (18 o´clock), half ways to 15 o´clock. Typical altered volume pot behavior. Note: this is not the fuzz face, this is the volume pot who´s law gets changed into somethink like super- logarithmic. Note also the typical loss in treble due to the cable capacity.



FF core driven by  a low impedance buffer (built in buffer disabled). Guitar= full volume (18 o´clock), half ways to 15 o´clock. Standard volume pot behavior restored. No loss in treble. Gets into Tonebender territory.



FF driven by built-in 10K buffer (and cable buffer). IMHO sounds and behaves not different than unbuffered, except pristine signal and functional volume pot travel.



FF alone, no buffers. Halfway FF thumped down with a clean booster in front. Hard drive. (Signal amplitude of booster way to big to be recorded). Note how little the volume increases. Surprisingly not too much change in tone. Gets definitely into TB territory.



SHAME. I fell for the age old trap.



"Louder sounds better"

- age old axiom and amongst audio circles well known wisdom                                                                 

I turned the  Fuzz control down and lo and behold... apart from a little difference in loudness, both variants sound largely the same! Explanation: the 10k resistor with the 2k input impedance forms a voltage divider, kind of an input attenuator. The FF stage gets hit way harder. Another theory up the swanee.

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Reference

[1]  Pink Jimi Photon, Schizoid Face, youtube
[2]  Pink Jimi Photon, Schizoid Face, freestompboxes.org
[3]  Pink Jimi Photon, Schizoid Face, diystompboxes.com

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Update History
  • Feb 6, 2020  update section on Mk-II switch
  • Jan 22, 2020  fixed switching pops caused by LED inrush current
  • Jan 20, 2020  minor functional updates
  • Jan 19, 2020  first release
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