BOSS HM-2 Mods

[dan5150]

I recently picked up a BOSS HM-2 "Heavy Metal" Pedal. I am in the processes of planning on doing some mods to it, mainly based on the HM-2 Indy mod.

One of my biggest complaints about this pedal is that the distortion control seems to have 2 settings, "little dirt" and "full on", there just isn't anyting in between.

In reviewing the schematic hosted on the Free Information Society: http://www.freeinfosociety.com/electronics/schemview.php?id=134

It looks the distortion pot is surrounded by a couple of cap/restistor filters. So my questions are:

Are these the right components to change to help make this control feel more "active"? If so, does anyone have any recomendations on new values?

Thanks,

-Dan-

[MartyMart]

I'd try playing with the 220k in the feedback loop after the pot and perhaps try a reverse log
pot for the gain control.

[Mark Abbott]

Dear Dan

How did you go with the HM-2?

After looking at the circuit. I would be lifting some of those diodes, the two that come to mind are the Ge diodes in series. After that I'd try the Tube Screamer diodes in the IC's feedback network. Even LED as the final diodes could be a good thing?

Just my two cents worth.

Yours Sincerely

Mark Abbott

[dirk]

I recently picked up a BOSS HM-2 "Heavy Metal" Pedal. I am in the processes of planning on doing some mods to it, mainly based on the HM-2 Indy mod.

One of my biggest complaints about this pedal is that the distortion control seems to have 2 settings, "little dirt" and "full on", there just isn't anyting in between.

In reviewing the schematic hosted on the Free Information Society: http://www.freeinfosociety.com/electronics/schemview.php?id=134

It looks the distortion pot is surrounded by a couple of cap/restistor filters. So my questions are:

Are these the right components to change to help make this control feel more "active"? If so, does anyone have any recommendations on new values?

Thanks,

-Dan-

The first thing I would do is to bypass the 2 germanium diodes after the distortion stage. They are the ones between the 2 10K resistors. These produce crossoverdistortion witch sounds harsh. Then you could remove the diodes and capacitor after the 2 germanium diodes. And as mentioned before the 220k resistor amongst others in the distortion stage determines the gain of the gain stage ic1b. The 47k resistor is a candidate for experimentation to. I don't fully understand how this part (feedback part with the filtering) of the schematic works, so if someone could explain that would be great.

[Mr. G.]

I'm interested in mods for this pedal as well, since I'm about to acquire one through a trade.