MI Audio - G.I. Fuzz (schematic)

tuemmueh · Post by **tuemmueh** » 01 Dec 2007, 00:02

Allright, I think it's time to pay something back to the community, so I traced my MI Audio G.I. Fuzz.
I love its tone and its great versatility!

No more talking, here is the schematic. Please contact me if you find any errors! That was the first pedal I've traced.
Btw., the pcb is very well done! It's about 5.5x2cm and all pots and the trim-pot are soldered on it. So I think pics wouldn't be that helpful, even if I had a cam

.

Thanks for everything!
Timm

madbean · Post by **madbean** » 01 Dec 2007, 01:12

Cool beans. Thanks for tracing this. Always up for another fuzz

bajaman · Post by **bajaman** » 01 Dec 2007, 02:45

Hi tuemmueh
many thanks for your good work - looks very tonebender like at first glance. thanks for sharing

bajaman[/quote]

analogguru · Post by **analogguru** » 01 Dec 2007, 06:52

Good job, tuemmueh !

I like the most: "No Mojo in here"

BTW, IMHO C4 is drawn in the wrong direction and should be reversed.

Here we go for the guts:
http://www.digimart.net/images/64/DS00200998.jpg
http://www.digimart.net/images/64/DS00200998_3.jpg

analogguru

snail · Post by **snail** » 01 Dec 2007, 10:42

Thanks!

tuemmueh · Post by **tuemmueh** » 01 Dec 2007, 23:14

analogguru wrote: BTW, IMHO C4 is drawn in the wrong direction and should be reversed.

You're absolutely right!
I updated the schematic and did some minor visual corrections, too ...

tuemmueh · Post by **tuemmueh** » 21 May 2009, 09:03

Sorry for bumping, but I wanted to attach the schem, so it won't disappear again when I delete it from my photobucket-account.

devastator · Post by **devastator** » 25 Aug 2009, 16:13

Hi,

I started to build that fuzz. I made the first stage , tested it and it doesn't boost, it's a buffer, it's normal or I did something wrong ?

devastator · Post by **devastator** » 26 Aug 2009, 17:32

I made it and I wonder if the values in the schematic are right. The sound is very buzzy and gainy.

the fuzz knob is tottaly useless, the tone control has too much bass (I compared it with the big muff tonestack and the cap values are higher in both side).

Liquids · Post by **Liquids** » 26 Aug 2009, 19:36

I love this thing. Check your values carefully.

The first stage is not just be a buffer, especially with the interaction of the load control. You must have something wrong, I dare say.

I found the fuzz knob very useful, and that particular tone control (I left that out of mine when I breadboarded it) is designed to be fairly wide ranged in both directions, neutral in the middle. The values are not the same as a BMP, as it is designed to be 'flat' in the center with no mid scoop with the 'body' control at full. The typical BMP is very bass shy on one side and very dark on the other, with a fair mid dip.

I don't find the circuit buzzy, especially if using the toggle switch tastefully, even with clean fender amps (though I think all fender bright switches should be neutered). It's one of the most jaw dropping fuzzes I've ever tried...if only I could get around to finalizing it...someday.

Keep the Bias and Gain trims at 1/2. Give it another look over. And another.

Use your breadboard and compare. Strip it down to the basic circuit, even -- load, fuzz, volume and you can plug in/out caps at the end to taste...sub a 1K for the 'bias' and 470R for the gain trimpots. Elminate everything between C8 and R11. Then you can know the range of tones it should start with, and if's your build, or just the other gear you are using it with that may be the issue...just one more reason why I think it's always best to breadboard everything first...

devastator · Post by **devastator** » 26 Aug 2009, 20:26

Yeah maybe I did something wrong. Actually I did some change on that circuit, So, perhaps is the cause of my strange buzzt sound. I didn't keep the "load" control and the gain trim (I connected the emetter directely to the ground).

Anyway, I've just made some modification: 47n output cap, 20uF with 2K2, remove the first stage, basicaly something more close to the original fuzz face desing.

I'll see that tomorow.

flood · Post by **flood** » 27 Aug 2009, 05:27

i tried making a neo fuzz workalike based on this schematic with a whole bunch of controls for a friend of mine. so far, the results have been kind of nasty in the latest iteration. thread, schematics, etc. all can be found here. i'm using OC141s for T2 and T3. it sounds nasty and horrible - misbiased in a big way, basically. huge volume drop, gated and like there's some octave going on in all settings. no sound or fuzz to speak of, just clunky fizz. it's unusable, basically. the first iteration (with the bax tone stack) actually sounded GREAT. i should have simply stuck with that and buffered the output.

https://www.freestompboxes.org/viewtopic.php?f=7&t=230

i'm going to strip it down and breadboard it soon as you've recommended. i've never had this much trouble with Ge trannies before, not even leaky ones.

devastator · Post by **devastator** » 27 Aug 2009, 11:23

you described exactly what I had with mine.

devastator · Post by **devastator** » 27 Aug 2009, 12:15

it's a pitty I can't edit my post instead of creating another one.

Well, I cut the 100K that links the base to the collector of the first transistor (in the fuzz face design) and that remove the buzzy gainy sounds, ". I'll add a capicator to tame a little bit the highs.

Liquids · Post by **Liquids** » 27 Aug 2009, 13:29

Here are two reference points for how it should sound.

http://www.mieffects.com/GIhearit.htm

http://www.proguitarshop.com/product.ph ... ategoryID=

Note that the 'bias' control is really best left alone at center for regular tones. It's probably more of a liability than a feature, and probably best replaced with a 1K resistor. Theres a lot of gain on tap here, so I saw no need for the gain trim, and made it 470R on the breadboard.

I felt the tones I was getting were better than the clips and videos above, actually, but it's a good starting point for what to expect. In these clips, they often set the 'body' control halfway, which creates a mid scoop that I don't care for. It's nice to have the body control, but if you look at the EQ curve, I feel it should be started full up (22k resistance total), which is flat. From there it can be backed off to taste, if you want less mids, rather than viewing halfway as 'neutral.' The drawback of having so many controls with so much range is there are a lot of nasty settings that should be avoided unless you get to know what you're doing...

I didn't try the germanium version, but the silicon version should be pretty easy...check your voltages and values. The transistors used are pretty hot. R2 and R6 serve to simulate 'leakage' and add some touch sensitive dynamics, darker, wolly, smoother sound, etc.

devastator · Post by **devastator** » 27 Aug 2009, 14:40

I've any problems with the tonestack part, it does what it has to, but maybe too many bass frequencies.

the main part, the fuzz face schematic is really ugly, the collector resistors seem to be pretty low compared to the "original" silicon version (R.G keen page I read yesteday). I don't think the 2K2 (in // with the 100uF) will change something, some Mayer fuzz have a 2K2 pot at this place.

So, in spite my change I didn't hear difference, still too gainy and buzzy. That sounds like a really high hain fuzz (like some "boutique" maker make) and absolutely not like a good fuzz must to be , for my ears of course.

I'm little bit desapointed 'cause I saw the proguitarshop.com video and I really liked the tone. How much that pedal in the market ?

Anyway, I'll continue to mod it to make a sound I like (I'll put the fuzz face values).

distortion_gfx1 · Post by **distortion_gfx1** » 07 Oct 2009, 01:33

thanks for the Schem

irmcdermott · Post by **irmcdermott** » 31 Mar 2010, 15:11

the links to the guts are dead. just wondering if someone knew what type of pots they used for the four across the top. the two on the end are awfully close to the edge. i'd like to build this one and lay it out close to the original. thanks!

MullisMan · Post by **MullisMan** » 21 Sep 2011, 18:13

I don't know if anybody still wants to build this, but here's a schematic, layout and transfer from Eagle. I put this together quickly and on a whim so there's some wasted board space, sue me. If anybody wants the Eagle files to improve on the layout let me know.

Also, when installing the BC549's, make sure to reverse the orientation that's on the layout. I didn't have a BC549 footprint so I used a 2N5088 footprint which has a pinout that is the opposite of the BC549.

Enjoy.