Guyatone - HD2 Harmonic Distortion  [schematic]

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JellyBelly
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Post by JellyBelly »

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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Post by jrod »

Yes! Please! Gut shots! :thumbsup

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Post by RnFR »

yeah, that one always seemed to be a nice sounding pedal. i'm interested!
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Post by JellyBelly »

all right, as soon as i find my camera i'll take some photos! 8)

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Post by JellyBelly »

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...
Attachments
100_2204.JPG
100_2203.JPG
100_2201.JPG
100_2196.JPG

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Post by Ben N »

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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Post by jrod »

thanks for the gut shots!!!

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Post by JellyBelly »

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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Post by soulsonic »

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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Post by JellyBelly »

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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HD-2 SCHEMATIC.PDF
Guyatone HD-2 Schematic
(47.39 KiB) Downloaded 530 times

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Post by RnFR »

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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Post by soulsonic »

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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Post by JellyBelly »

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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Post by Ben N »

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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Post by JellyBelly »

Hi, i reuploaded the schematic beacause it was no longer online!
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HD-2 SCHEMATIC.PDF
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Post by Chrisfromiowa »

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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Post by EmmG »

Has anyone cloned this/ have a layout?

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Post by Manfred »

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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Post by EmmG »

Jellybelly's schematic download link still works:
https://www.freestompboxes.org/download/file.php?id=18502

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Post by EmmG »

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