I love messing around with HM-2s. This is a super simple mod and very useful. Adding a clean blend to the mighty HM-2
I have done this enough times to have a modified schematic drawing with where to add/cut stuff in.
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Modified Schematic |
First thing to do is open up the pedal and move the wires around and drill a hole for the pot. I use a 9mm pot as there isn't much room in there.
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Guts and hole drilled |
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HOLE! |
Now I take my 9mm pot and put some 80mm (approx.) fly leads on it and then mount it into the hole, put the nut and washer on and tighten.
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Wires soldered on |
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Mounted |
Next I build up my little blend PCB. I have designed a PCB for adding to any circuit to add a clean blend. As long as they are in phase it works great for only a handful of components. I don't sell this PCB it's just for me. Alternately if you want to do this mod you can use
this. It's a vero layout of the same circuit I have made a PCB of. I'm not taking credit for the circuit it's not mine. I do however use a 100N cap instead of a 10N as I found it sounds better.
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My little PCB |
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All ready to go |
So now with my PCB made and the 9mm blend pot installed all I need to do is wire it into the HM-2. To do this I need to cut 1 track on the HM-2 PCB. This track is after the volume but before the FET bypass switching system (as labelled on the schematic above).
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Locate the trace at pad #8 |
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Trace cut with Exacto knife. |
Now with the trace cut I can start soldering wires onto the main PCB. Two wires from the 9mm Blend pot, Pin 3 and Pin 2 go onto where the cut trace is. Pin 3 goes to Pad #8 and Pin 2 goes to the other side of the cut trace which connects to C32.
Time to connect up the rest of the wires. To do this I have to find the input to the effect on the effect side of the FET for the bypass switching system. Q4 is the FET doing the switching. I need to solder the send wire to the daughter board to somewhere at the junction of Q4, C6 and R16. Blend Pin 1 connects to the daughter board after the 10uF cap. V+ of the daughter board connects to the main board at Pad #2. GND of the daughter board connects to the main board at Pad #3.
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Start connecting daughter board |
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Find Q4 |
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Power wires soldered on and location of Q4 Traces on PCB |
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Ready to test |
With everything now soldered in it;s time to test the mod. Tested it with no issues. Now I need to secure the daughter board with a bit of the old hot snot glue, attach a knob to the pot, put it all back together and send it off the customer.
So that's how you mod an HM-2 to have a blend control. This is a pretty easy mod to do even for a beginner. If you have any questions or comments add them below
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Testing |
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Ready to send. |
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