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I'm back to Exar pedals tracing, I was a bit busy during the last weeks, and it took me almost a month to finish HM-02 Heavy Metal tracing. According to the pots and warranty card dates, the unit I have seems to be produced and sold in 1999.
It was challenging to trace because of a lot of wiring with resistors in heat sinks attached to them. PCB itself is single-sided and "transparent" in light.
Because of its name, you might guess it should be a Boss HM-2 clone, but the Exar pedal has nothing in common with that circuit . The gain stage is a discrete op-amp, almost part-to-part copy of Boss DS-2. Then it has Volume control placed before the EQ. And EQ itself is not based on gyrators but a complex active filter network with a mixer stage at the end. I don't think I've seen exactly the same EQ in any other pedal, so my guess is Exar engineers designed it. I wanted to check if I traced EQ correctly and did a SPICE simulation in CircuitLab https://www.circuitlab.com/circuit/eh92 ... -hm-02-eq/ . It works in the simulation, so I believe it is correct. Attached is the schematic with buffered bypass switching omitted.

I analyzed EQ a bit. So we have a 3rd order Sallen-Key lowpass filter (I just drew it a bit unusual, you could play with it here http://sim.okawa-denshi.jp/en/Sallenkey3Lowkeisan.htm ) for Low; it cuts everything higher than 90 Hz. For High we have a bunch of highpass filters at 1.5kHz and 15kHz. Then lowpass and highpass filters get mixed with an unfiltered signal (Mids potentiometer). If you set Low and High at 0, you'll get only unfiltered distortion, which sounds nice.