Earth Sound Research - Graphic Fuzz  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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induction
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Post by induction »

Forumite insonicbloom has a cool electronics blog with schems and veros for all manner of interesting things, including a floating power supply using a 555 chip. It seems like this would be a simple way to make this effect daisy chainable. Granted, it will more than double the parts count, but that's not saying much with this circuit.

Maybe it's not as clever as whatever Jimmy Behan did, but it should do the trick, I think. If I'm wrong or have overlooked something, please set me straight.

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Post by agoldoor »

I'm pretty sure if you emailed Jimmy he'd tell you what he did. He is very generous with his knowledge.
jimmybehan @ g m a i l . c o m

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Post by induction »

I finally bothered to look up 'comparator' on Wikipedia, and now I understand how this circuit works, more or less. It's surprisingly simple, so I'll offer my 2 cent analysis. The open loop gain on an op-amp is theoretically infinite, so if the voltage on pin 2 goes above the voltage on pin 3, the output saturates at the lowest voltage the chip can output. When pin 2 goes below pin 3, the output saturates at the highest voltage the chip can output. Voila: square waves.

To work correctly, the DC voltage on pins 2 and 3 must be the same. The original schematic accomplishes this by tying both pins to ground. Pin 3 connects to both ground and the 1/2-rail voltage via a divider on the battery (which implies that the battery gives +/-4.5V, so adapters won't work unless the adapter is isolated and doesn't share ground with anything else in the chain). Pin 2 is held at ground by DC coupling the input. In principle, an input cap would not change the operation of the circuit, but a pulldown resistor might be necessary on pin 2 (I'm not sure).

But there are other ways to skin this cat. Pins 2 and 3 have to have the same RMS voltage, but it doesn't have to be ground. So we can tie the negative battery terminal and pin 4 to ground (or use a normal adapter instead, daisy-chained, even), and break the ground connection to pin 3 (which means that pin 3 is now at 1/2-rail voltage). Now we add an input cap and supply a 1/2-rail DC offset to pin 2 via a second voltage divider (or a maybe a 2 Meg resistor to the existing divider). Then you'll just need an output cap, since the RMS value of the op-amp output won't be 0V anymore.
ESR_Graphic_Fuzz_schem_my_mods.png
This is simpler than the floating power supply I suggested above (only 4 extra components), but seems like it should work just as well. I haven't breadboarded it yet, though, so a grain of salt or two might be in order. I have no idea if this is the approach Jimmy Behan used or not, but it should allow for standard power supplies and input jack switching.

Or, sure, you could ask Jimmy what he did. His solution might be better.

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Post by Nocentelli »

induction wrote:But there are other ways to skin this cat.
This works fine on the breadboard, sounds very much like the +/-4.5v version. The oscillation seems maybe higher, but i can't swear i'm using the same 741 (if that would make a difference). To my untrained eye, it looks very much like the version posted by PRR in the DIYSB thread (https://www.diystompboxes.com/smfforum/ ... #msg903540) but with 1uF in/out caps and the 2M2 between pin 2 and 3. Removing this resistor makes no noticeable difference.
Steven_M wrote: 21 Jan 2011, 17:52
biffa wrote:Sorry,but u r not the only member here
I'm not? Well fuck this site then. I only want meaningful conversations with myself.

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Post by Goodrat »

Hey guys, I worked at ESR as one of the two technicians there in the customer service repair. It was back in 1978 and my first electronics job. Sometimes we would just play guitar all day.
What I remember about the Graphic Fuzz box is they oscillated like crazy. The other Tech, Tony, made some improvements.
As far as the schematic, I remember there were two 10K resistors as a divider with the center going to ground to make the +/- supply and whatever caps on that.
The IC was a 741.
A lot of amp designs were ripped of from Peavey and they got in trouble eventually for that..

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induction
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Post by induction »

FWIW, the reversed Level control at the output has a drastic effect on the oscillation/cocked wah frequency. It's very interactive with the Frequency pot, and in fact doesn't really function much like a volume control, except at its lowest settings. It's actually easier to control the resonant frequency with the Level control than with the Frequency control, which is more useful for adjusting the distortion characteristics. My approach: use the Frequency control to dial in the right amount of existential despair, and use the Level control to fine tune the oscillation/cocked wah sound.

If I was going to label the knobs on this thing, the knob now called Level would be called "Frequency", and the knob now called Frequency would be called "Travis Bickle".

If you want a Volume control that actually, you know, controls the volume, just add a traditional volume control after the Level control.

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Post by rossics »

Came across this layout a while back on tagboardeffects, can't seem to find it there anymore,
Has anyone ever tried it out?
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ESR-Graphic-Fuzz.png

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Post by Nocentelli »

I believe it was pulled because it didn't work.
Steven_M wrote: 21 Jan 2011, 17:52
biffa wrote:Sorry,but u r not the only member here
I'm not? Well fuck this site then. I only want meaningful conversations with myself.

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Post by larsjm »

Just a quick observation, which may explain why most people get lots of whine from this circuit, if they can get it to work at all. If you look at the pictures of an original unit, the battery ground wire clearly attaches to a switched input jack: http://4.bp.blogspot.com/-i5lDSHm3KuE/T ... G_0551.JPG. To my knowledge, the way that type of power switching works is that it connects the negative battery terminal TO THE GROUND OF YOUR GUITAR CABLE. That being the case, it therefore connects the negative battery terminal to EVERYTHING that is connected to chassis ground. So why is it that people are saying you need to isolate the negative battery lead from the other grounds?

It wasn't isolated in the original pedal.....

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Post by larsjm »

To get the most out of this pedal, you also need to install an offset null control for the 741. This can be done with a 10k linear pot connected to pins 1 and 5, with the wiper to ground. This gives you tons of control over the fuzz sound, and IMHO is more effective than the filter control. In fact, on mine I just leave the filter on full and tune it with the offset null control. Lots of great, gated, sputtery fuzz sounds there!

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Post by tabbycat »

Nocentelli wrote:Many thanks to peeps and intripped for the advice
Nocentelli wrote:works now! Oscillation aplenty, tweaking begins tomorrow.
hey nocentelli, am glad you got this brat to beat.

did you use peepsthecat's vero layout or intripped's schematic eventually?
am loving the yt demo you posted (why can't all demo's be like that?)

there are a mix of options, schemos and veros, some of them with (possibly) unresolved issues and some already dismissed. obviously all efforts are noble and to be applauded, it's a jungle out there in 'uncharted effect land'.
it looks like a not overly complicated build to get into, but (obviously) would like to start at the most promising beginning, if it is that straightforward and not a composite of parts of each.

thanks, tabbycat.
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Post by Nocentelli »

Steven_M wrote: 21 Jan 2011, 17:52
biffa wrote:Sorry,but u r not the only member here
I'm not? Well fuck this site then. I only want meaningful conversations with myself.

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mods: joyo voodoo octave cap rotation, dan echo r10 mod, pb&j r10 mod, behringer vintage phaser true bypass mod, behringer sf300 superfuzz diode switch (germanium-silicon).
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Post by tabbycat »

many thanks, nocentelli.

i have yet to breadboard a whole pedal yet. just cobbled together separate individual sections to add a clipping stage, or a tone stack. maybe this is the one to start with. will update as and when.
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Post by Nocentelli »

larsjm wrote:Just a quick observation, which may explain why most people get lots of whine from this circuit...
Apparently, that's an original feature:
Goodrat wrote:Hey guys, I worked at ESR as one of the two technicians there in the customer service repair. It was back in 1978 and my first electronics job. Sometimes we would just play guitar all day.
What I remember about the Graphic Fuzz box is they oscillated like crazy....
Steven_M wrote: 21 Jan 2011, 17:52
biffa wrote:Sorry,but u r not the only member here
I'm not? Well fuck this site then. I only want meaningful conversations with myself.

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mods: joyo voodoo octave cap rotation, dan echo r10 mod, pb&j r10 mod, behringer vintage phaser true bypass mod, behringer sf300 superfuzz diode switch (germanium-silicon).
vero layouts: earth sound research graphic fuzz (posted here).
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Post by tabbycat »

Nocentelli wrote:
larsjm wrote:Just a quick observation, which may explain why most people get lots of whine from this circuit...
Apparently, that's an original feature:
Goodrat wrote:Hey guys, I worked at ESR as one of the two technicians there in the customer service repair. It was back in 1978 and my first electronics job. Sometimes we would just play guitar all day.
What I remember about the Graphic Fuzz box is they oscillated like crazy....
maybe i'm just a bratty noisenik but i like the self-oscillation whistle with the fuzz. makes it dirtier, spacier.

but there's a recent clone out there that seems to have minimalised the whine to satisfy all the lightweights (don't you raise your handbag at me...)

so i thought i'd i'd post the with and without version demo here for the sake of comparison.

"be a good animal, true to your instincts" (d.h. lawrence).
"there is no excellent beauty that hath not some strangeness in the proportion" (francis bacon).
"ni dieu ni maître" (anarchist slogan).

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Post by allesz »

Damn, the sound of this effect is soo cool too mee.
I really have to give it another try, I got some 741 (and I must say I like this chip).
Apart from the oscillation the fuzz sound is really nice.

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mods: joyo voodoo octave cap rotation, dan echo r10 mod, pb&j r10 mod, behringer vintage phaser true bypass mod, behringer sf300 superfuzz diode switch (germanium-silicon).
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Post by tabbycat »

just been out in the 'hood, more s&d than r&d. a-ducking here, a-diving there, a-stretching here, a-skewing there...

earth sound research pcb shots separate (solder side flipped horizontally to match component side view)...
esr graphic fuzz pcb separate.jpg
and blended.
esr graphic fuzz blend pcb copy.jpg
pcb of original esr graphic fuzz photo-plopped for your amusement.

tabbycat.
"be a good animal, true to your instincts" (d.h. lawrence).
"there is no excellent beauty that hath not some strangeness in the proportion" (francis bacon).
"ni dieu ni maître" (anarchist slogan).

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mods: joyo voodoo octave cap rotation, dan echo r10 mod, pb&j r10 mod, behringer vintage phaser true bypass mod, behringer sf300 superfuzz diode switch (germanium-silicon).
vero layouts: earth sound research graphic fuzz (posted here).
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Post by tabbycat »

links to photos showing offboard wiring, to join the dots.

http://www.thegearpage.net/board/showth ... 94&page=29
"be a good animal, true to your instincts" (d.h. lawrence).
"there is no excellent beauty that hath not some strangeness in the proportion" (francis bacon).
"ni dieu ni maître" (anarchist slogan).

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mods: joyo voodoo octave cap rotation, dan echo r10 mod, pb&j r10 mod, behringer vintage phaser true bypass mod, behringer sf300 superfuzz diode switch (germanium-silicon).
vero layouts: earth sound research graphic fuzz (posted here).
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Post by tabbycat »

links all over here for this

anybody ever mess with the ESR Graphic Fuzz?
http://www.freestompboxes.org/viewtopic ... 28&t=22621

Earth Sounds Research Graphic Fuzz
http://www.freestompboxes.org/viewtopic ... 33&t=17755

Earth Sound Research - Graphic Fuzz
http://www.freestompboxes.org/viewtopic ... aphic+fuzz

all with schematics of sorts.

maybe a merge in order.
"be a good animal, true to your instincts" (d.h. lawrence).
"there is no excellent beauty that hath not some strangeness in the proportion" (francis bacon).
"ni dieu ni maître" (anarchist slogan).

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Completed builds: completed builds: shinei univox 6tr superfuzz with mods, vox repeater, earth sound research graphic fuzz, roland ad-50 double-beat fuzz, shinei fy-2 companion fuzz with mods, ampeg scrambler, fender blender, ep3 18v pre, dam meathead fuzz, coloursound inductorless wah, lpb1.
mods: joyo voodoo octave cap rotation, dan echo r10 mod, pb&j r10 mod, behringer vintage phaser true bypass mod, behringer sf300 superfuzz diode switch (germanium-silicon).
vero layouts: earth sound research graphic fuzz (posted here).
Location: i could tell you but i'd have to kill you.
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Post by tabbycat »

found some nice gutshots of this today, don't know how i missed them before. have to click on the for full image because they are huge.

Image

Image

Image

original post here with lots more pics http://retrotonejunkie.blogspot.co.uk/2 ... -fuzz.html

thanks to retrotonejunkie for the blogpost thing. i hope you don't mind me reposting the gut shot pics here.
"be a good animal, true to your instincts" (d.h. lawrence).
"there is no excellent beauty that hath not some strangeness in the proportion" (francis bacon).
"ni dieu ni maître" (anarchist slogan).

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