DRY AND WET KNOBS: These two knobs control the volume levels of the dry, boosted path and the wet, “chainsaw” path. When either one is down, it disappears from the mix. These two circuits are in parallel, so you can mix both sides to your taste or rig.
EMPHASIS: The stock HM-2 circuit gives you two “color mix,” or EQ knobs: L(ow) and H(igh). The “L” knob controls a frequency boost at 87Hz, but the “H” knob actually controls two different bands simultaneously, at 958Hz and 1279Hz. The Carbide keeps these three boosts intact, but the Emphasis control cuts frequencies around these bands, making them pop a little more. Like the “H” knob of the original, the Emphasis control adjusts two different filters simultaneously, one at 63Hz and a treble shelving filter. The Q of the low filter is just wide enough to butt up against the onboard bass boost. while knocking out pesky sub bass.
The Carbide accepts a center-negative DC power supply from 9 to 15 volts, capable of supplying at least xxmA of current (over is fine). Plugging in anything other than this (center-positive, AC, higher voltage, etc.) will potentially brick the Carbide. I cannot recommend doing this. Check your supply and make 100 percent sure it says all the right stuff. If you plug in the wrong supply, you’ll immediately send your pedal to the shadow realm. Even though that sounds pretty cool, your Carbide doesn’t want to go there, this I can promise.
I grew up with metal, and even then I was hard-pressed to identify the HM-2 sound. Early adopters of that circuit were none other than… Eric Clapton and David Gilmour? Yeah. Well. As it turns out, only a handful really knew what the term “heavy metal” meant back then. And for those who did know, the sound of the HM-2 was not quite in-line with the knowledge base. Clapton and Gilmour used one with the Dist(ortion) control all the way down, instead putting its powerful EQ to work.
I grew up in a small town without a record store or music scene long before the Internet existed, and when Entombed’s “Left Hand Path” came out, I didn’t hear it and neither did anyone I knew. I was also in grade school, but that’s beside the point. I didn’t hear it until much later in my life, and when I finally got around to listening to it, another band using the HM-2 had already captured my attention. That band is called Magrudergrind, and the song “Bridge Burner” from their 2009 self-titled record is bathed in dimed HM-2 tones.
When I started building pedals as a hobby, the HM-2 circuit wasn’t really in my sights but after hearing that record, I spent an unhealthy amount of time poring over that circuit and its associated applications. I’ve built them with tons of knobs, I’ve built them with a sole volume control, and I’ve built every configuration in between. When it came down to utility though, I found myself really riding one control not offered on a stock HM-2, a wet-dry blend.
The humble blend control is a powerful one; it automatically makes a pedal bass-friendly, and it allows you to toe the line between breath-stealing crunch and something a little more homogeneous to an overall band mix. My only gripe with a standard blend is that it’s not a one-size-fits-all solution—it can be hard to balance volume between a dry, buffered signal and a screaming distortion circuit. However, the parallel clean boost and distortion circuits do just the trick.
I optimized the HM-2 circuit for “more,” akin to the marginal gains theory but with a little more oomph here and there. There’s a more refined, musical clipping arrangement, adjustments to filter values to really let those palm mutes chug, and a different transistor selection for a little extra gain. Overall, it’s just, as I said, “more.”
The Emphasis control came to me a while back when I worked on the Dreamcoat and realized the power of reducing key frequencies to make others pop. “Tight” controls in some pedals work in a similar fashion; they let the mix “breathe” by cutting low frequencies so you and your bass player aren’t engaging in open fisticuffs. You’re gonna like this one.