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From the parts I've examined it looks like a classic rat with no significant changes to the schematic.The JFET seems to be wired like that, single gate resistor to ground.
It would be rather instructive to find videos comparing low and medium gain amps playing jazz, country, pop etc
It's probably worth noting that the when the HM-2 was replaced by the HM-3 they did away with that 2 transistors + op-amp gain setup in favour of a single opamp whose gain was set by altering the feedback resistor which is a much more conventional setup.
It's IC1a in the diagram: http://i.imgur.com/dlIsUiW.jpg
They also removed the series clipping diodes, used transistor gyrators in the filter section, and maybe tweaked some values but otherwise the circuit topology is essentially the same.
New...ish 9V battery.
Pedal switched on, input grounded. all knobs maxed.
Measured using a Fluke 117
Battery voltage measured between pin 2 (9V in), and 3 (0V) on the board: 8.27V
IC1 Voltages:
1: 4.14
2: 4.14
3: 4.11
4: 0
5: 3.63
6: 3.63
7: 3.62
8: 8.27
Q7 Voltages:
1 E: 7.58
2 C: 3.63
3 B: 6.98
3. I would definitely recommend a 2.1mm center-pin-negative power jack, as that has become a virtual standard for pedals, and will work with most power supplies.
