Boss - HM-2 Heavy Metal

soulsonic · Post by **soulsonic** » 24 Jan 2009, 06:57

Totally salvageable. With a little TLC, you could probably have it up and running in an afternoon.
Are there any cracks in the board? That's not hard to fix... scrape off the green stuff, use a thin wire as a bridge and solder over the cracks. Take some 20 or 22 gauge stranded wire and pick out an individual strand to use for the thin wire. Once you've done it a couple times, it's easy.

Skarrgus · Post by **Skarrgus** » 24 Jan 2009, 07:19

This isn't really related to the HM-2, but... Do all of the older Boss pedals have that weird yellow shit all over the circuit board? I noticed it on my DF-2 and one of my MT-2's but not the MD-2, TR-2 or later Metal Zone... What the fuck is it?

mugician · Post by **mugician** » 24 Jan 2009, 07:38

Glue would be my guess.

No cracks. Problem here is that I don't want to use those pots or that extra board that connected to the main board via the ribbon thingy (can't remember what they're called), and I don't exactly know how to re-wire the thing.

Ah! I've also been meaning to ask this: is there any advantage (taking out the size factor here) to using full sized pots over the mini ones? And what kind of pots am I supposed to use for this thing?

I don't know how to read schematics, so I imagine I'll have a bit of trouble finding out how to wire the jacks, switch, LED, and pots and what not.

Does anyone know how these things sound?

mugician · Post by **mugician** » 24 Jan 2009, 18:39

I also wanna replace those old Mitsubishi IC's. And maybe a couple other "key" components to audiophile quality - or is it an 'all or nothing' kind of thing when it comes to the quality of components?

Any ideas on IC's? What kind of pot would I use to get *less* gain?

mugician · Post by **mugician** » 24 Jan 2009, 21:57

You see, I don't know how to read schematics. Eventually I'll get someone to teach me, but for now, I'd like to wire my HM-2 PCB up this weekend.

I'm doing this with 3 10k audio/log pots for the level, high and low, and a 100k audio/log for the drive. My understanding is that the 100k will give me less overall gain than the 250k on the schematic, yes? Also, on the schematic it says to use a linear pot for the level... but wouldn't an audio/log pot be preferable?

EDIT: it says on the schematic to use 10 Linear pots for the *high and low* control. Again, wouldn't audio be better for this type of control?

I'm also doing this with a true-bypass switch.

Basically there are a bunch of numbered solder pads at the top of the board and since I'm not using the daughter board that holds the pots in regular Boss pedals (I'm re-housing this in a 1590bb), I can't just line it all up. All the holes are numbered, but obviously I don't know which numbers are ground, in, out, LED, and all the pots etc...

Would anyone happen to have an idea on how to help me re-wire the PCB?

Thanks so much!

mugician · Post by **mugician** » 24 Jan 2009, 22:14

What if I replaced the M5218L (these are what are on my HM-2 PCB) IC's with some JRC4558L's? How would that sound?

Oh, oh, oh... I think I'm slowly figuring this out... how about this (this is my understanding): the M5218L IC's are super high-gain op-amps, and the JRC4558L is an op-amp sporting not as much gain? So if I used three JRC4558 IC's in place of the stock ones, I'd get less gain and more character? - I should clear up that I don't play heavy metal and have no need for a super super super high gain pedal. - So is this derivation correct? Semi correct? I mean, gain has to do with clipping, so the stock diodes are still going to clip the signal a whole bunch, but it's the IC's efficiency or whatever, that ultimately dictates how much gain I'm going to get, right?

Forgive me for not being very electronic-savvy.

JJ Gabor · Post by **JJ Gabor** » 25 Jan 2009, 01:01

Nice find!

I have an Hm2 and love it's sound, It has a a really interactive tone circuit.

mugician · Post by **mugician** » 25 Jan 2009, 01:11

Yeah, I'm really looking forward to giving this thing a make-over. New enclosure, sweeter LED, nicer jacks, switch...

I was also thinking of replacing the IC's with some single-in-line JRC4558's. Or maybe socketing the three IC spaces and use a switch (or three) to switch between stock and the JRC's. Wait - is that possible?

moltenmetalburn · Post by **moltenmetalburn** » 25 Jan 2009, 15:13

The HM -2 was the first pedal i ever modified. I changed around 85 parts in this pedal! most of it was just upgrading to metal films or caps. I did replace the germanium diodes wit red leds as per brian wamplers mods. IN the end the hm-2 never sounded any "better" Im gonna say this one is really love/hate.

mugician · Post by **mugician** » 25 Jan 2009, 19:08

moltenmetalburn wrote:The HM -2 was the first pedal i ever modified. I changed around 85 parts in this pedal! most of it was just upgrading to metal films or caps. I did replace the germanium diodes wit red leds as per brian wamplers mods. IN the end the hm-2 never sounded any "better" Im gonna say this one is really love/hate.

Wow. I guess I'll just have to wait and see. But there won't be problem when I change out the IC's will there?

moltenmetalburn · Post by **moltenmetalburn** » 25 Jan 2009, 21:32

I haven't changed out the ICs but i bet if you used these adapters and put something like opa2134 in all those spots maybe things will get interesting. while your at it try tlc2272 and 4558s too!

http://cimarrontechnology.com/so8dip8to ... 60301.aspx

Now you have me wanting to experiment with mine more! thanks!

mugician · Post by **mugician** » 25 Jan 2009, 21:38

http://cimarrontechnology.com/so8dip8to ... 60301.aspx

Wow! Those look pretty cool! Actually, the 4558's I found are single in line - no need for an adapter. I will check that out!

I bought a couple of these for checking out different IC's:

http://www.smallbearelec.com/Detail.bok?no=101

soulsonic · Post by **soulsonic** » 26 Jan 2009, 08:10

If you look at the schematic, there is a couple transistors before the main distortion stage - sort of a boost circuit. I bet you could get some interesting changes by messing with those. One of them is a PNP... try sticking a germanium in there! Some people have tried that with a Blues Driver with success. Also, you could have a switch to short across the two Ge diodes - to shunt around them, taking them out of the circuit. That would turn off the gating effect. The subtle gating is cool for keeping a tight sound at loud volume - one of the things the HM-2 excels at - but it pretty much smashes the dynamics to nothing. The diodes to ground immediately following them is where I would try LEDs. If you look carefully, you can see a potential Midrange control hidden in the tone control section... you just need to add the control and get the necessary parts re-routed; I've done this successfully with a DOD American Metal (an HM-2 clone) to give it separate treble and bass controls like the HM-2 instead of the crappy single tone control that sounds awful.

I haven't bothered to try getting an HM-2 because I have the DOD that does the same thing, but they can be had for almost nothing on ebay, so I may as well get one (or two or three) to use as guinea pigs for modding and fun.
I have an MT-2 that I've been meaning to mod, but I haven't bothered to make time for it yet.

moltenmetalburn · Post by **moltenmetalburn** » 26 Jan 2009, 14:39

Also, you could have a switch to short across the two Ge diodes - to shunt around them, taking them out of the circuit. That would turn off the gating effect. The subtle gating is cool for keeping a tight sound at loud volume - one of the things the HM-2 excels at - but it pretty much smashes the dynamics to nothing.

I swapped these germaniums out for red leds, they are actually for gating and provide no clipping function? Ill have to try removing them all together.

If you look at the schematic, there is a couple transistors before the main distortion stage - sort of a boost circuit. I bet you could get some interesting changes by messing with those. One of them is a PNP... try sticking a germanium in there!

Any suggestions on transistor type? I haven't done much with transistor swapping in the past.

If you look carefully, you can see a potential Midrange control hidden in the tone control section... you just need to add the control and get the necessary parts re-routed; I've done this successfully with a DOD American Metal (an HM-2 clone) to give it separate treble and bass controls like the HM-2 instead of the crappy single tone control that sounds awful.

Would you please elaborate?

mugician · Post by **mugician** » 03 Feb 2009, 20:17

- three in the feedback loop of the opamp, for asymetrical soft clipping (à la OD-1). To remove these, you'll have to desolder one leg in each brach.
- two germanium in series, which seems to be quite specific to the Boss "metal" pedals. To remove these, you'll have to shunt them (connect a wire across).
- two silicon to ground, typical hard clipper like a DS-1, a Rat, a MXR Dist+, etc. Again, to remove these, you'll have to desolder one leg of each.

To shunt the Ge diodes in series and the Si's to ground, I have to desolder one leg of each diode and jumper each pair of open pads? How come you don't just completely remove them?

I just re-housed the HM-2, and don't really like the sound. I was thinking of bypassing the hard-clipping and only using the soft asymmetrical clipping and possibly using a warp control in the feed-back loop to further my options. Am I on the right track? What about replacing the diodes in the feed-back loop? Or using two different types of diode in the warp control? Am I getting the warp concept right? - http://www.muzique.com/lab/warp.htm

I'm trying to learn all of this stuff, but I don't really know where to look. Everything I google is already a little too technical and over my head and the search option on the site doesn't really work for me usually.

moltenmetalburn · Post by **moltenmetalburn** » 03 Feb 2009, 23:22

I was cheering you on until this:

American metal bands have really taken to copying Swedish melodic death metal, bands such as At The Gates, but they neglected adopting the signature guitar tone, opting for the bland, ubiquitous dual rectifier sound. The fools.

Have you ever heard Darkest Hour, God Forbid, Machine Head, All That Remains, Killswitch Engage, The Black Dahlia Murder these are a few American bands highly influenced by Swedish death/thrash who all use healthy doses of mids. I see less and less rectifiers these days than you think. In fact the list goes on and on, Id say the scooped metal tone these days is reserved for the hardcore and nu metal bands, there are few american death/thrash bands playing recs, too sloppy/mushy, slow transient attack, lower mid mush emphasis.

IMO FWIW

mugician · Post by **mugician** » 04 Feb 2009, 01:49

Anyone? The pedal is just sitting open on the workbench (kitchen table with a cardboard mat). It's been there all day. Does it matter which legs of the diodes I unsolder? What do I jumper, the empty pads together?

Greg · Post by **Greg** » 04 Feb 2009, 02:06

If you just want to get rid of the diodes, you can remove the silicons completely, the germaniums are connected in series with the circuit so they'll need to be jumpered or it won't work.

The questions you asked are a matter for experimentation to suit yourself, so can't really be answered.
Why don't you try removing the diodes to ground (hard clippers) and see if you like it ?

mugician · Post by **mugician** » 04 Feb 2009, 02:29

But more about the jumpering part. Which lead do I unsolder?

Greg · Post by **Greg** » 04 Feb 2009, 02:46

mugician wrote:But more about the jumpering part. Which lead do I unsolder?

I don't have a HM-2 to look at, but you would need to remove both diodes and jumper across where they were... just jumper one diode position and leave the other empty will be OK.
You can post a pic of the circuit board (both sides) if that isn't clear and I'll have a look and try to explain better.

Boss - HM-2 Heavy Metal [schematic]