Sunday, 5 February 2023

Exar HM-02 Heavy Metal

 As many others, I thought this was just a clone or a close derivate to the Boss HM2. We couldn't be more wrong. Vitali from drunk beaver pedals opladed a schematic for it and it reveals a quite an interesting circuit. The distortion section resembles Boss DS2 with a discrete op amp and hard clipping diodes.

The 3-band eq section is fairly unique. Mid control is basically a volume control for the raw unfiltered signal. Low is built around a 3rd order Sallen key filter and the High control is driven with an active dual high pass filter not dissimilar to one of the filters found in EHX Knockout.

The layout turned out quite big with all these transistors and op amps so it is intended for a BB enclosure.



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