Modifying Korg KDM-2 metronome for one-hand operation



This is a nice metronome, in that all functions can be operated from single controls, rather than control sequences. Its only disadvantages are that the flush-mounted speed knob is hard to operate, even with two hands, and impossible with only one. So, if you want to adjust speed up a by a few beats, you have to grasp the unit with both hands, and it’s still awkward. Also, the settings for the number of beats per measure can’t be adjusted with one hand, since the unit will slide backwards with the applied pressure.
Two modifications solve these problems:

  1. Change the tempo control knob to a standard instrument knob.
  2. Angle the unit back on a heavy stand so it stays put when the other knobs are operated.

The tempo control is an encoder with no stops – it spins freely, and puts out two pulse trains whose time relationship shows the direction of rotation. The encoder provided has a female fitting, and the plastic knob that fits into it is male. There’s no convenient way to make the knob stick out further, so the encoder was replaced with another unit with a shaft that an instrument knob with a ¼” hole can be attached to.
The encoder used was a Bourns PEC11-4125F-S0018, bought from Mouser Electronics for $1.68. After the original encoder is removed, the new one can be soldered into the same holes. The new encoder has the additional feature of a normally open switch actuated by pushing on the control shaft. This switch can be wired in parallel with the unit's “gear shift”, the third button from the right on the bottom row, which changes the rate of tempo change from four bpm per encoder pulse to one bpm.
The second problem, a firm angled mounting, was solved with some strips of scrap aluminum and an old piston pin for weight. If I had it to do over, I might try to make something out of weighted plaster of paris, because the bottom of the metronome has an irregular shape when it is angled away from the horizontal, and it's hard to get it level.

Document by John O’Flaherty
quiasmox at yahoo dot com

Click thumbnails to expand view...

Original

Disassembled

back


old control


new control


front new control


reassembled

with knob



with weighted stand