Guyatone - HD2 Harmonic Distortion  [schematic]

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Guyatone - HD2 Harmonic Distortion

Postby JellyBelly » 08 Oct 2009, 10:59

Hi! first post here...
I own a little mean Guyatone HD2, a distortion/fuzz pedal, plenty of gain and very bright... The manufacturer's website claims it is similar to a 70's Big Muff, but I've never made any confrontation... The sound is very good, very "harmonic" :) but it lacks a tone control... I guess with some little mods it could be a great effect.
I could try and take some gutshots if anyone is interested...
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Re: Guyatone HD2 Harmonic Distortion

Postby jrod » 08 Oct 2009, 15:35

Yes! Please! Gut shots! :thumbsup
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Re: Guyatone HD2 Harmonic Distortion

Postby RnFR » 08 Oct 2009, 15:59

yeah, that one always seemed to be a nice sounding pedal. i'm interested!
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Re: Guyatone HD2 Harmonic Distortion

Postby JellyBelly » 09 Oct 2009, 08:21

all right, as soon as i find my camera i'll take some photos! 8)
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Re: Guyatone HD2 Harmonic Distortion

Postby JellyBelly » 14 Oct 2009, 09:05

Here are the gutshots... my camera isn't very good at macros :P
IC is a JRC4558, transistors are 2 c1815 and 3 k30a
I'm gonna send Guyatone an email, and ask if they could send me the schematic, because the circuit is pretty damn tight...
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Re: Guyatone HD2 Harmonic Distortion

Postby Ben N » 14 Oct 2009, 10:13

Maybe an opamp Little Big Muff or Muff Fuzz with buffered bypass? Sure ain't a BMP... BTW, I had a number of those tiny Guyatone pedals (not this one) some years back, and sold them all because of their significant tone-sucking--not a good bypass at all, whatever it is.
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Re: Guyatone HD2 Harmonic Distortion

Postby jrod » 14 Oct 2009, 14:58

thanks for the gut shots!!!
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Re: Guyatone HD2 Harmonic Distortion

Postby JellyBelly » 15 Oct 2009, 08:00

So the guys @ Godlyke kindly sent me the original schematic...
i've read the forum rules but i didn't understand if i can post it or if i have to redraw it...
or perhaps i could just upload it to an hosting site and post the link?
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Re: Guyatone HD2 Harmonic Distortion

Postby soulsonic » 15 Oct 2009, 08:08

You can attach it to a message here with the upload feature at the bottom of the reply screen.
Or you could send it to me to re-draw. :wink:
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Re: Guyatone HD2 Harmonic Distortion  [schematic]

Postby JellyBelly » 15 Oct 2009, 08:36

all right, here it is!
:D
i hope i can come up with some mods to make it more "usable"... for example, a tone control, or a true bypass mod...
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Re: Guyatone HD2 Harmonic Distortion

Postby RnFR » 15 Oct 2009, 09:25

hmmm... so it looks muff-like with a few differences. IC input and makeup stages, no muff-tone control, no true bypass, and what probably has the biggest impact on it's tone(besides lack of tone control), is the pair of 1n60's on the output of Q1 causing crossover distortion. maybe that's the "harmonic" in the HD2? haven't seen that mod in a muff circuit before, looks interesting...
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Re: Guyatone HD2 Harmonic Distortion

Postby soulsonic » 15 Oct 2009, 09:49

Thanks!
It looks like all the components for the tone control are there, it is just permanently wired in the halfway position. You could remove R8 and R7 and replace them with a 100k control wired as is normally seen in a Big Muff.
Can you see the value of R9 on your unit? The value in the schematic is missing or incorrect.
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Re: Guyatone HD2 Harmonic Distortion

Postby JellyBelly » 15 Oct 2009, 10:21

soulsonic wrote:Thanks!
It looks like all the components for the tone control are there, it is just permanently wired in the halfway position. You could remove R8 and R7 and replace them with a 100k control wired as is normally seen in a Big Muff.
Can you see the value of R9 on your unit? The value in the schematic is missing or incorrect.

i'll try and take a look, but as you can see from the gutshots all the components are mounted "upways" (dunno if it's the right term, sorry, i'm not a native english speaker :oops: )

so a switch to include/exlude the1n60s could turn it into a more "classic" muff?
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Re: Guyatone HD2 Harmonic Distortion

Postby Ben N » 15 Oct 2009, 12:06

Well, I'll be. I'm so used to seeing discrete in/output buffers on opamp-based circuits that it didn't occur to me that they'd sandwich the heart of a Big Muff between opamp stages, but it does make sense. Pretty cool.
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Re: Guyatone HD2 Harmonic Distortion

Postby JellyBelly » 08 Jun 2012, 19:11

Hi, i reuploaded the schematic beacause it was no longer online!
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Re: Guyatone HD2 Harmonic Distortion

Postby Chrisfromiowa » 04 Jan 2018, 19:46

JellyBelly wrote:all right, here it is!
:D
i hope i can come up with some mods to make it more "usable"... for example, a tone control, or a true bypass mod...

I just got one of these in a trade and it has a broken switch and led, fixed the switch and still havent figured out the led, but did you ever figure out a True Bypass mod? I'm sure this is similar to one of the old MXR spdt switches, right? Thanks, and I know this is half a decade old... regards Chris
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Re: Guyatone - HD2 Harmonic Distortion

Postby EmmG » 05 Jan 2018, 06:42

Has anyone cloned this/ have a layout?
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Re: Guyatone - HD2 Harmonic Distortion

Postby Manfred » 05 Jan 2018, 12:47

EmmG wrote:Has anyone cloned this/ have a layout?


I could make a PCB-layout clone according the shots above, but all attachments does not exist anymore.
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Re: Guyatone - HD2 Harmonic Distortion

Postby EmmG » 05 Jan 2018, 13:32

Jellybelly's schematic download link still works:
download/file.php?id=18502
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Re: Guyatone - HD2 Harmonic Distortion

Postby EmmG » 05 Jan 2018, 13:44

Image
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