BOSS HM-2: Like an Ever Flowing Gleam

The BOSS HM-2 Heavy Metal guitar distortion pedal holds a special place in death metal history. It is the sound of Sweden. This cheap, compact design pedal was used heavily at Sunlight Studios to make the “buzzsaw” guitar tone famous on so many original Swedish death metal records from Entombed, Dismember, Nihilist, At the Gates, and Edge of Sanity; later, on scores and scores of not so memorable imitation records.

BOSS HM-2 Heavy Metal pedal

In fact, that’s pretty much all this pedal can do. Dynamics? Forget it. Put all levels on 10, detune, and jam. Of course, there’s some amp EQ details in there somewhere, but forget it. This pedal gets so much worship for such a one-trick pony. My old band mate, Leon del Muerte, is one of those worshippers. He liked the light plate I added to my old Phase 90 and wanted his HM-2 to get the same treatment. Sure, the HM-2 already has a power indicator light, but he wanted it to SHINE like the god he saw it as. I took it from his apartment as he hugged it goodbye and I went to work (2 months later).

I had to figure out how and where to add the extra LEDs for the light plate. I would run leads from the power source of the original LED power indicator under the circuit board and embed the LEDs into the acrylic light plate that would be the new bottom of the pedal.

BOSS HM-2 inside

I measured and cut some 1/8″ thick acrylic that would be the light board. It was fitted to the exact dimensions of the bottom of the stomp box and 1/8″ holes were drilled for the screw holes and the holes where the new LEDs would live.

light plate

I had to get new screws for the base and the acrylic plate, as the old ones were too short. #4 sheet metal screws from OSH fit the bill as replacements. In this case, I need 3/8″.

BOSS HM-2 with light plate

The 3mm orange LEDs I used run very bright, but are also quite directional. To help diffuse the light more evenly, I burnished the sides and flattened the top with some fine grit sand paper. This also help them fit nicely into the acrylic plate.

LEDs for light plate

On the schematic, I identified the placement of the resistor that was responsible for the -voltage drop to the LED. I was planning on running three higher voltage orange LEDs parallel, so R46 had to be replaced to allow more power through. Using Ohm’s law: Resistance needed = (9v power – 1.8v LED) / (24mA x 3 LED Amperes) = 100 Ohms.

BOSS HM-2 schematic

Luckily, this circuit board is conveniently labeled because I suck at tracing circuits. R46 is swapped out for a 120 Ohm resistor, the next size up from my calculation to be on the safer side. I only have 1/4″ watt resistors and this board was made for 1/8″ watt resistors. Doesn’t matter, just bend the legs and it works fine.


I replaced the original red power indicator LED at D14 with one of my orange ones and left the legs intact. These would be leads to a separate PCB to supply power to the other LEDs.

adding LED to BOSS pedal

A little circuit board was all I needed to distribute power to all the LEDs. I soldered four wires to it and then soldered the board to the legs of the LED at D14. I had to carefully twist the legs of D14 and make sure they weren’t touching so the new board would fit inside the pedal.

HM-2 light mod

The pedal is reassembled and the leads for the new LEDs are threaded between the circuit board and the original plastic insulator.

BOSS HM-2 plastic

The LEDs are soldered to the leads and I put heat shrink over the legs for even more insulation. The acrylic light plate is fitted over them and the LEDs sit snugly in their new homes. Screw it all back together, and time to fire it up.

BOSS HM-2 Plastic plate

Awesome. Looks like Sark stopped mucking about with light cycles in the Grid and is gonna play some hot lixxx on Tron’s grave!

modded light BOSS HM-2

This was a totally unnecessary mod done entirely for vanity. I have no problem with that. Musicians invest a lot of time and money into gear. When something works out and is precious, why not treat it that way? It’s a lot better than trashing disposable, cheap garbage and flooding craigslist with your detritus when you’re down on rent.

P.S. If you’d like to learn more about the BOSS HM-2 Heavy Metal pedal, check out these awesome videos and links! But for God’s sake, don’t ever crack open a book.

Swedish Death Metal author Daniel Ekeroth demonstrates and talks about the HM-2’s importance to Swedish death metal:

Benash Surrey’s online petition to get BOSS to start producing the HM-2 again:


Wikipedia page history of Swedish death metal with short mention of HM-2
Official BOSS product page for HM-2
Hobby schematic of HM-2 and circuit info
BOSS entry and info about HM-2


2 thoughts on “BOSS HM-2: Like an Ever Flowing Gleam

Leave a Reply

Your email address will not be published. Required fields are marked *