hex fuzz add on for the gr707 guitar synth

[pinkjimiphoton]

circuit by Wayne Joness from gr300.com

this is a daughterboard you can add to the roland gr707 synth to add a hex fuzz to it, which it doesn't have.
fringe item, i know, but since i am making one for mine, i figured someone could use it.
wayne's original was on a piece of weird stripboard from radio shack, but i adapted it to vero.

i modified it to have a trimmer instead of a fixed resistor for the opamp gain, and made it slightly "hotter" than the original so there's some wiggle room to make it a little gainier. i find often the hex fuzz is a blt lower volume than the synth signal, that should help.

i made it overly complex, really, as i added cuts to extra tracks and made all that stuff connect to ground to keep noise down. it could be simplified by eliminating those cuts and jumpers, i doubt they have much effect, but just in case... sometimes vero stuff can get a little weird tonally due to the interaction between the rails and the inherent capacitance created.
a ways back i was building some vero versions of a popular pedal the company i work with puts out, and the vero version just sounds better than the pcb version.. warmer, darker.
so i got some pcb's being laid out for a "fake" vero .... basically a pcb that apes a vero board, but all the cuts already made. weird idea, but i suspect it should "sound the same" as the actual vero builds that way and will save me a lot of time.

wayne specs 1n914s or bat46 for the clipping diodes, i have a gazillion bat41's so i use them.
he also specs a tl082 for the chip, i hate jfet chips for guitar distortion, so am socketing it. i expect a 1458 will as usual sound better in it so that's what i spec'd

yeah, i know. but my ears tell me that that sounds glassy and jagged <jfets distorted> are not for me.

anyways... pics

my layout:




wayne's original schem:




original layout:






the original circuit adapted from the roland guitar controllers




more deets here:

https://www.joness.com/gr300/g-707_hex-fuzz-output-modification.htm

hopefully some poor soul out there will find this useful someday

i was rather surprised when i saw how simple it really is... for all intents, each string is passively buffered and mixed into one input with a simple clipper. no input or output caps needed!

all credit to dr. wayne joness for the cool toy!

[pinkjimiphoton]

awww fudge, just realized i buggered up that layout... will up the corrected one in a minute...

[pinkjimiphoton]

corrected. sorry peeps

[Rodgre]

You are my hero. You know that, right?

Thank you!

Roger

[Rodgre]

Wayne Joness is also my hero. Ha!

Why do you not like jfets for distortion circuits? Teach me something!

Roger

[iainpunk]

Wayne Joness is also my hero. Ha!

Why do you not like jfets for distortion circuits? Teach me something!

Roger

i think he meant MOSFETS instead, as that't what the OpAmp in question uses for its internals. the TL0x2 series have some harsh artifacts when forced to clip, the BJT opamps don't have that. its a subtile difference, but the xx58 opamps don't have such a harsh/nasty top end (except the 358, but its a different, ever worse type of harshness, crossover distortion).

cheers

[Rodgre]

I get that. If not pushed to their limits, their characteristics are more or less a wash, though? They don't get ugly until they clip? This is the stuff I love to know about!

Roger

[iainpunk]

as long as an opamp is way within its limits, they all sound the same* but when pushed out of its comfort zone, opamps can be made to sound quite different. distortion and fuzz circuits often push the envelope and make the opamp clip, where overdrives, and all non-drive circuits often don't do this.

a good example of this is the Rat, using the LM308, which has a limited Gain Bandwidth Product, smoothing out the distortion a bunch. some people will mention the slew rate here, but the frequencies the slew rate affects in the rat can be 16kHz (at best, 100kHz is more realistically whats affected) and up, which guitar amp's cant even dream to reproduce enough for that to matter. there are slower opamps tho, where the slew rate can actually affect the sound.

an example of a pedal where people claim it matters is the TubeScreamer, but the opamps operate well within operating limits, and most people don't hear the difference there.

then there's deliberate chip abuse, like my Xenos overdrive.

cheers,
Iain

* not all of them tho, the LM358 is a good example, it exhibits crossover distortion even when fully within its limits, this adds a fizzy kind of distortion that gets stronger if the signal it puts out gets smaller. sounds awful, but i use it deliberately in my latest project to add nasty fizz to an already nasty sounding distortion

[ElectricDruid]

The weird thing about this circuit though is that it *doesn't* seem to use the op-amp for much of anything bar a little bit of make-up gain.

There's a 10K and a pair of back-to-back diodes to ground on the way in, so we'll clip the input signal at +/-0.6V or so. Then there's the op-amp, wired as an inverting stage with 100K/120K, so a gain of x1.2 (+1.5dB), which is "subtle" at best. The 120pF gives a roll-off above 10KHz or so, but since that's the cutoff (-3dB) we're only -9dB down at 20KHz, so that's not limiting anything much except ultrasonics. There's no real drive control beyond the level going in, and there should be virtually no tone added by the op-amp in such a situation.

2 cents,
Tom

[PRR]

.......opamps don't have such a harsh/nasty top end (except the 358.....

Only an automotive fuel-gauge designer would call the LM324 (or its dual) an "opamp", without the prefix "crappy".

Yes, I know in very light loading (such as guitar-chain inputs) without bat-screech highs the crossover *may* not rise up and bite you.

[antonis]

The weird thing about this circuit though is that it *doesn't* seem to use the op-amp for much of anything bar a little bit of make-up gain.

I'm pretty sure for it comes as a fragment of an unstated circuit..
Guitar strings inputs replace some kind of amp output (like MXR Dist+)..
Maybe it serves just for impedance issues..

edit: My bad.. Jimi already posted its origin..
(which calls for non-inverted outputs where Jimi's circuit inverts..)

[pinkjimiphoton]

hahaha i just followed the schematic the good dr joness posted! lol

gonna build this up as soon as i get around to it.

i'm the original @#$% jfets guy. i like mosfets, but jfets sound like ass when they clip and in general are nothing but a huge pain in the ass to work with in my experience.

distorting mosfets sound like tubes. CLEAN jfets can sound ok, but dirty ones sound glassy and jagged and hissy, and i really can't stand 'em.

thats why i always specc'd 1458's for the crap i used to build and design for that company. their original circuit was popular, but really didn't sound that great til some changes were made.

i think the "jfets sound like tubes" thing is pretty much a fallacy, at least to my ears. but ymmv

[pinkjimiphoton]

Wayne Joness is also my hero. Ha!

Why do you not like jfets for distortion circuits? Teach me something!

Roger

hey roger,
i don't like jfets in general, they're always a pain in the ass if ya need matched sets, they're expensive and did i mention a pain in the ass? lol

they can sound great in some circuits and applications, particularly when a clean guitar is what you're looking for.
they can sound great also with proper filtering <i haven't found proper filtering, personally, yet to make 'em sound good to my ears> i guess in some dirt boxes,
but for distortion i think they sound like ass. glassy, brittle sounding uneven fuzz that's hissy, noisy, and not a good sound.

take almost ANY dirt box with an opamp in it, and replace it with a 1458 or a 741 and its almost always instant nite and day... sounds more amp like.

way less high end after clipping = much less harsh, musical distortion.

when i began working for the last guy, they were using expensive high end jfet based chips.
the complaint was they needed more edge to them blah blah. changing to the more primitive... and way cheaper... opamps
definitely improved the distorted tone... from glassy and earbleeding to warm and inviting.

of course, now they're using them in every product they huck. not that i had any influence on that...lol

but anyways, that's why i don't like jfets.

i gotta 80's marshall 2x12 solid state combo.
it sounded great until ya cranked it full... the it was so goddamned hissy and noisy even with my decimator pedal i couldn't nuke the hiss.

so i took it out of the truck... i'd been using it live.... and opened it up. i expected to maybe have to add a snubber, there's a couple spots in the preamp with free pads if ya need them... and it had ALL the chips replaced with socketed tl072's.

i removed the first one, and replaced the preamp with a 1458 as the guv'nor intended.

suddenly the tone improved ridiculously, but still a hissy mess. ditching the other 72's and restoring the proper xx58's did the trick... no more hiss, no more noise, no more earbleed.

that's my story, and i'm stickin' to it

[pinkjimiphoton]

Wayne Joness is also my hero. Ha!

Why do you not like jfets for distortion circuits? Teach me something!

Roger

i think he meant MOSFETS instead, as that't what the OpAmp in question uses for its internals. the TL0x2 series have some harsh artifacts when forced to clip, the BJT opamps don't have that. its a subtile difference, but the xx58 opamps don't have such a harsh/nasty top end (except the 358, but its a different, ever worse type of harshness, crossover distortion).

cheers

hahahah ya beat me to it lol

[Processaurus]

Very cool!! I have wanted to do a hex fuzz with my GR700 for a long time. Lots of crackpot ideas on how to work it in to the synth (sub hex fuzz as oscillator 2, in each of the synth voices; post filter Pre envelope; post envelope Pre chorus- lots of options...).

So is this mod just to get hex fuzz from the G-707 guitar when it is hooked up to the GR300 floor unit or are you using it with the GR700 somehow?

[ElectricDruid]

Well, *that* circuit makes a lot more sense! It's got a level control going in, a *lot* more gain, and the diodes *after* the gain. So much more standard stuff and much more what I'd expect to see.

So is the earlier graph-paper diagram that Jimi posted just a bad trace, or is it what happens from the 10K to the diodes and then afterwards (a bit of make-up gain) - so simply a partial circuit, rather than a wrong circuit?

[antonis]

I should vote for a "partial" circuit but Jimi insist for a fully operating one..

[pinkjimiphoton]

Very cool!! I have wanted to do a hex fuzz with my GR700 for a long time. Lots of crackpot ideas on how to work it in to the synth (sub hex fuzz as oscillator 2, in each of the synth voices; post filter Pre envelope; post envelope Pre chorus- lots of options...).

So is this mod just to get hex fuzz from the G-707 guitar when it is hooked up to the GR300 floor unit or are you using it with the GR700 somehow?

in my case, it will let me use the hex fuzz with my gr300, and i can tap it off with a 24pin thrubox/13 pin adapter pedal i got from a chap named yohan over in france.

i likes hex fuzz. it can be a useful sound.

[pinkjimiphoton]

Well, *that* circuit makes a lot more sense! It's got a level control going in, a *lot* more gain, and the diodes *after* the gain. So much more standard stuff and much more what I'd expect to see.

So is the earlier graph-paper diagram that Jimi posted just a bad trace, or is it what happens from the 10K to the diodes and then afterwards (a bit of make-up gain) - so simply a partial circuit, rather than a wrong circuit?

lol...
yeah you're right, but thats from a completely different guitar. this fuzz as made by wayne is an addition to the circuitry already in the guitar, not the complete circuit itself.
no idea why he changed the inputs etc, i just laid out what he came up with. it definitely works, a lot of guys have installed it.

[pinkjimiphoton]

naaaaah, its the complete circuit that wayne posted,

BUT its just a partial circuit, if you wanted to make it standalone i doubt it would work. but when grafted into the g707 guitar, supposedly its good.

i have NOT had a chance to build it yet to see if it works. but a lot of the guys who follow the gr300 site apparently have used this to good effect, so i assume the rest of the circuit is built into the guitar itself.

i'd have to compare schematics, just too @#$%in' lazy atm lol