The KM‑50 is a simple metronome made by Korg in around 1983–84. I have never seen one in real life, or photographs apart from catalogues from the period. And now this.

It’s a very basic device, simpler than the earlier Korg RT‑10, consisting of a timing pulse with a higher-frequency sound as a bar pulse. It also has a needle timing indicator like a miniature physical metronome. The timing range is set with a rotary switch, from 40 to 208bpm. The bar pulse can be from 2/4 to 6/4 or off. And it has a tuning pitch, which varies from an unusual 439 to 444Hz, the frequency set with the same linear switch as the bar pulse. The frequency is pretty accurate but wavers very slightly. It takes 9V DC external power or can be powered by a battery. (Unusually for products of this age it seems to work quite well with a rechargeable battery.)

Like many other metronomes, the sound it makes from its built-in speaker is quite irritating and I doubt I would be able to focus on music with that going on. Unfortunately, while the sound can operate without the needle, the sound can’t be switched off separately, unless a cable is plugged into its signal output. It has a 3·5mm TS jack for this, and this rather more interesting. Checked on the oscilloscope, the normal signal is a +8V rectangular pulse which fades out slightly at the end. The bar pulse seems to go through a resonant filter.

I won’t be using this as a metronome in the ordinary sense, but a stepped +8V pulse generator means a timing source that could be run into one or more synth clock inputs, with appropriate attenuation and/or inversion, and even though this seems extremely rare in the secondhand market, it was cheaper than the majority of simple Eurorack timing clocks I’ve seen. I don’t have any specific plans at the moment but it’ll probably be useful at some point.

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