This is a library of perfboard and single-sided PCB effect layouts for guitar and bass. I'm not an electrical engineer by any stretch of the imagination, just a DIY'er who likes drawing layouts. It is meant for the hobbyist (so commercial use of any of these layout is not allowed without permission) and as a way to give back to the online DIY community.

Monday, October 19, 2015

Boss HM-2 Heavy Metal

The HM-2 is the godfather of all other heavy metal distortion stompboxes. While it was first introduced in the '80s, it's still a highly regarded circuit for metal applications with its high gain and crushing lows, especially if you live in Sweden. Said crushing lows are thanks to the gyrator tone stack (not something you see all that often). Original units only have high and low tone controls, but it's easy to add a mids control, and the layout below reflects that. If you don't want the Mids control, simply connect the Mids 2 pad to lug 2 of the Highs pot. It's a fairly big layout, but you should be able to fit it in a 125B without issue, and if you're really precise with your drilling you might able to squeeze it into a 1590B.



Update July 13, 2016: 
Updated the layout so that the ICs are getting full 9v. Tone stack pots may need to be reduced to 10k.


28 comments:

  1. I´ve spotted an error on the layout. The left side of the bottom 68k resistor (R25 on the orignal schematic) should go to the +9v rail, not to +4.5V bias, just move it one row the right

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    1. You can pass the circuit diagram the Boss HM-2 Heavy Metal ?

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    2. Well, I'm looking at the schematic he used and that's not a 9v rail. They're both connected to 4.5v. it's a modified schematic without any buffers. I even tried connecting it to that rail. I still can't get any sound out.

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    3. Come to find out, that 68k-to-9v rail is a typo in the original schematic. It's supposed to go to ref 4.5v.

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    4. No typo at all (I have yet to find an error on original Boss schematics/service notes). Checked it on my original HM-2, it goes straight to the 9V rail. Also tested voltage with ohmeter. Bottom 68k GOES TO 9V!!!!

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  2. I tried the project but not had sucesso.pode exist substitute for trasistor 2sc2240 and 2sa970 ?

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  3. There's some serious wrong stuff in this layout. All the ICs VCC somehow connected to a 4.5V VB; next, there's 100K pots in tonestack instead of 10K pots; tonestack pots lugs are inverted (you should interchange 1 and 3). Maybe that's not even all. I've built it and it doesn't work. Now I'm checking the layout, will update it later if it will finally work as it should.

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    1. Not sure how you're reading the layout, but the ICs all connect to 9v at pin 8 as per the datasheet. The red traces are 9v, the yellow 4.5v, green ground, and blue audio signal. Pot lug numbering is outlined in the General Layout Notes tab at the top of the page. You probably just count them differently. The tonestack pots are 10k on the schematic that's floating around online, but I indicated 100k to give better sweep of these frequencies. This is also the values given my lvlark on his stripboard layout, which is verified. I've triple checked the layout to the schematic and it checks out. Check you build for bugs and use an audio probe to help find any errors.

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    2. Yes, i made a mistake about 4.5V, but +VCC on ICs is wrong anyway. It must go straight to 9V, but somehow it goes to this part of schematic: https://i.imgur.com/zVCX14M.png That way there's about 4.5V (don't know why, checked it with a multimeter), that's why I said, that it goes to 4.5VB. I cut the red trace and connected it straight to 9V, and it actually worked: https://i.imgur.com/RMb6R6q.png Before there was only some hard-gated crackle going from the device.
      I don't think I'm wrong about tonestack lugs, because i have actually built it and tone works backwards, but drive and volume are not, they're fine. Of course I've counted all lugs the same way. See for yourself: lugs 1 of tone must go to the positive input of IC (https://i.imgur.com/1XqoRoW.png), but on your layout it actually goes to a negative input: https://i.imgur.com/A2n9ksI.png.
      It semi-works now, but the sound is very strange, i am going to check the build for any errors. Tonestack works weird, there's a very huge boost of frequencies right on the upper edge of pots. Is it supposed to work that way? Can it be because of 100K pots instead of 10k? And if not, can you give me a hint, what might be wrong? Thank you for your reply.

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    3. I'm surprised a 1k resistor would pull the voltage down that far. I can tweak that on the layout so the ICs are getting the full 9v. The nice thing about this layout in this case is that the pots are not board mounted, so you can easily swap pot lugs around. And by all means try using 10k pots for the tone controls. I based this heavily off lvlark's stripboard layout and there didn't seem to be any hangups with 100k pots. I'll revisit the layout when I get a chance and fix the voltage rail.

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    4. I don't think 1k resistor pulls the voltage down to ~4.5V by itself, maybe there's not enough current for all ICs connected that way? When I cut the trace there's something like 8V on that particular rail. Seems fine to me. I will try 10K pots and see if it helps.

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    6. thank you.por check this project because I did not do this funcionou.vou modifications vc described .

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    7. I have installed 10K pots instead of 100K and now tone control works a lot smoother on the upper edge, but I have another problem: there's not much gain even with gain maxed out. And if I turn gain very low, the sound is heavy-gated. Can it be because of me using kta1268/ktc3200 pair instead of 2sa970/2sc2240 (haven't been able to find them)? Maybe there's some another decent substitutes out there?

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    8. OK, I have resoldered some stuff and now it works just fine. Only real mistake in the layout is +VCC of ICs not going in the right place. And it's better to use 10K pots instead of 100K, or adjustments won't be as smooth as it should. Another interesting thing I have found is about that 68K resistor going to 4.5V, on some schematics it's going straight to the 9V VCC. Some guy has found that it actually SHOULD go to 9V instead of 4.5V. That's how it is in the original BOSS HM-2 pedal. You can read about it here: http://www.diystompboxes.com/smfforum/index.php?topic=109663.msg1004112#msg1004112
      I've tried both options and didn't hear any difference.

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  4. I want to congratulate for this wondrous site , muito.muito thank cool the design of the pedals .

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  5. There's a BOSS HM-2 clone called DOD American Metal(https://i.imgur.com/nQlzdUQ.jpg) and that "R25" 68k resistor goes straight to full 9V as in original BOSS schematic, so it actually MUST be that way, it's another mistake on this layout. Please fix it.

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    1. Thanks for the work. I thought I was losing my mind with mine not working.

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  6. What about that 68k resistor? I want to build this one but this 'mistake' confuses me... is it verified or does this 68k thing still exist?

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  7. hi, is this layout verified? I read all the comments but couldn't understand if anyone's successfully built it...

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  8. Hi, I built this with 100k pots for Low-Mid-High & the 68k resistor connected to the 4.5 V (orange) rail, and I don't get any sound. I can't find where the problem is. Is the schematic verified?

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  9. Nevermind, the problem was not the circuit but my power supply :D

    I tested it with another one on a cheap 15 Watt Fender amp so the sound was not really to its full potential! The sound can be really "boomy" (lots of bass frequencies, especially with my guitar tuned to drop A). Add some gain on your amp and you can get the famous Swedish Death Metal "chainsaw" sound by slightly tweaking the Mids and High potentiometers. Instead of putting the gain on my amp (which is really bad), I added a ProcoRat2 clone right after the HM-2 -- I felt I could unleash hell! The sound is really, really dirty but not muddy, you can really hear the different notes, it's not just noise. By tweaking differently, I was quite surprised to discover that I could use it as a overdrive-ish pedal (not really distortion, not really fuzz... Quite undefinable but some might use it). I never tried the original HM-2 but this sounds like all the bands I like (Bloodbath, Entombed...). So thanks a lot for this schematic!

    *** THIS LAYOUT IS VERIFIED ***
    (tested with 100k pots for Low-Mid-High and 68k resistor connected to the 4.5 V (orange) rail)

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    1. Awesome! Thanks for verifying and the build report!

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    2. No worries :)
      For those interested, I managed to fit this in a 125B enclosure. A 1590B might do the trick too but I wouldn't try it, it was hard enough for me to fit everything in the 125B!

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  10. I have build this & it works. Thanks for this layout

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