News:

SMF for DIYStompboxes.com!

Main Menu

Boss HM-2 Mods

Started by jwbink1500, December 27, 2011, 09:47:49 PM

Previous topic - Next topic

jwbink1500

Hi all,

I have a Boss HM-2 that I modded withe distortion mods via Brian Wampler's books and the sound improved. Didn't do the tone mods yet though.

My problem is the Distortion pot on the pedal has a small increase in distortion initially to a plateau from about 10:00 to 3:00 then increases again. Does anyone have a way of altering this? I would like more range from the distortion and to remove the dead spot. I'd like to hear any other mods anyone has tried. I loved the Heavy Metal Setting on a Boss GT-6 so I though I'd try this pedal but always sounds fuzzy and not very clear or powerful.

Thanks
Joel

Mark Hammer

The gain control should not do that.  It would seem the pot is dirty or otherwise malfunctioning.

jwbink1500

Thanks for the reply Mark.

I don't think it should either but I have read other posts with the same behavior. See this post: http://www.diystompboxes.com/smfforum/index.php?topic=58370.0 There is no scratchiness and the transition is smooth  up to a point then it maintains the dist then continues again. No big sudden jumps when turning the pot. The other post never really got the problem solved so I thought I'd try and get some ideas.

What does anyone think?

Thanks
Joel

Mark Hammer

Just for the heck of it, try bridging the pair of germanium diodes with a piece of wire on the copper side of the board, and see if that makes a difference in the behaviour of the gain pot.  The thing with the HM-2 is that there are three different sets of diodes to introduce clipping, as you can see here: http://www.freeinfosociety.com/electronics/schemview.php?id=134 .  Where two of those sets do not impair the circuit's ability to pass signal, the GE diodes present a kind of "wall" where, unless the signal is above their forward voltage, no signal will pass.  My suggestion is to take that "wall" down temporarily and see if it makes a difference in the behaviour of the pedal.  It will certainly change the tone, so don't confuse that with the behaviour of the Dist pot.

jwbink1500

Thanks Mark,

I'll give it a try when I get the chance. Might be a bit though. Just had a baby boy on Dec 21st so there goes my time! :D Not a bad thing though.  ;)

I'll post the results when I get them.

Thanks
Joel

Jurgen

This is a known issue with the HM-2. The distortion increases from minimum to about 9 o' clock on the gain pot, then stays pretty much constant until about 3 o' clock, after which it ramps up again. I'm quessing it has to do with the way the gain control is implemented, simultaneously functioning as a variable ground leg resistance in a voltage divider after the gain stage built around Q6 and setting the resistance to ground in the feedback loop of IC1B, as you can see on the schematic here: http://www.freeinfosociety.com/electronics/schemview.php?id=134

Mark Hammer


Renegadrian

#7
resurrecting an ol' thread, just got a HM-2 with a broken pot for cheap. (I have to find a 9mm pot, regular one don't fit in the box)

Spent the whole afternoon modding it, trying new things and implementing known mods (wampler)

ACA to PSA mod is mandatory.
D6-D7 diodes are out.
Removed C28
subbed all 1µ electros in the signal path with non electros (C3, C4, C12, C15, C32)
C30 is now a 47n from the original 68n

tried to implement the mids pot, mmm I don't think it's that useful...
tried to remove D8-D9 or put leds instead of Si - mmm nope, sound is bigger but I don't llike how the notes fade out.

output buffer removed, wire #6 is wired to q10/r48

For now, the main mod is the removal of C28, it give a whole different sound at the end of the high pot. and yeah those germ diodes out.

I'll report other mods if I find something new...
Done an' workin'=Too many to mention - Tube addict!

gorgieboy

Resurrected again!
Mine is broken, began to sound very sloppy and dirty all of a sudden, do you recommend doing this mod to trie to fix it or do you have any other ideas?

gorgieboy

Or anyone for that matter....?

bluebunny

If it's broken, then fix it first.  Otherwise you're modding from a completely unknown starting point.
  • SUPPORTER
Ohm's Law - much like Coles Law, but with less cabbage...

gorgieboy

Ok, asking as a layman, what should i start with? Where do i start with the failsearch?
I'm not a soldering veteran so i'm a little lost. Got som basic soldering skills though....

Kipper4

If it where me I'd start a new thread.
eg "My HM 2 failed, help me debug or fix it."

Thouroughly look at the pcb and componants with a magnifier to see if you can see any possible areas of concern.

Go here
http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

follow up with the debug info posted in your thread.

Be a little more precise about what it does and doesnt do.

"began to sound very sloppy and dirty all of a sudden,"
could mean so many things it's hard to tell where to start.

I hope we can get you sorted.

Welcome to the forum :)
Rich

Ma throats as dry as an overcooked kipper.


Smoke me a Kipper. I'll be back for breakfast.

Grey Paper.
http://www.aronnelson.com/DIYFiles/up/

czech-one-2

Quote from: gorgieboy on January 11, 2017, 02:34:50 PM
Resurrected again!
Mine is broken, began to sound very sloppy and dirty all of a sudden, do you recommend doing this mod to trie to fix it or do you have any other ideas?resurrecting an ol' thread, just got a HM-2 with a broken pot for cheap. (I have to find a 9mm pot, regular one don't fit in the box)

Spent the whole afternoon modding it, trying new things and implementing known mods (wampler)

ACA to PSA mod is mandatory.
D6-D7 diodes are out.
Removed C28
subbed all 1µ electros in the signal path with non electros (C3, C4, C12, C15, C32)
C30 is now a 47n from the original 68n

tried to implement the mids pot, mmm I don't think it's that useful...
tried to remove D8-D9 or put leds instead of Si - mmm nope, sound is bigger but I don't llike how the notes fade out.

output buffer removed, wire #6 is wired to q10/r48

For now, the main mod is the removal of C28, it give a whole different sound at the end of the high pot. and yeah those germ diodes out.

I'll report other mods if I find something new...

Just want to chime in to save any other potential modders a headache. The 'remove the output buffer,wire #6 to Q10/R48 is nonsense. I did it and while there was a slight improvement in the tone, all my true bypass pedals had footswitch 'pop' downstream. Not recommended....