MXR 185 MIDI Interface


Something of an unusual item in MXR’s catalogue, given they were much better known for their effect pedals and studio gear, the 185 Drum Computer was an early digital drum machine which launched in 1983. Rumour has it that it was developed with some input from Roger Linn, but I don’t know if this is true or not. It does share a similar multiplexing system to the LinnDrum though. While stuffed full of EPROMs to hold the sounds, it uses a linear 8-bit DAC and encoding scheme so unfortuantely they’re not interchangeable with machines which use the more common mu-Law format.

I’d been on the hunt for one for several years and at long last managed to land one from the States for a very good price. It was filthy and needed a fair amount of work doing to get it back into shape, but did essentially work. They’re seemingly quite rare – having kept an eye on serial numbers of ones appearing on online auctions, I counted about a dozen units ranging up to 1403 (mine is 513). With the distribution fairly even in this range, I suspect MXR may have only built 1500 of them and who knows how many are still in existence.

With relatively few made, it’s little surprise that it did not end up on many records, despite being favourably reviewed at the time. While it offered a good feature set and a compelling price on its launch in 1983, the Roland TR-707 which came out just over a year later and at about a third of the price surely must have cut its life short. Nevertheless, the fact that it wasn’t widely used makes it interesting in its own way, as the sounds aren’t immediately familiar.

MIDI Retrofit

As it did not ship equipped with MIDI, I developed this retrofit for it. The goal was to keep it simple and non-invasive. It gives you MIDI IN and THRU, the sockets for which are fitted in existing cutouts in the case using supplied mounting panels. It allows for triggering all of the drum voices from MIDI notes, with accent controlled by note velocity, and can also sync the internal sequencer to MIDI clock. All of the MIDI settings are made by holding down drum trigger buttons during power-on, and are stored in non-volatile memory.

There are three clock modes: internal, where the sequencer will run from the internal clock as normal and ignore MIDI clock; MIDI clock, where the internal clock is disabled; and automatic, where it will switch back and forth between internal and MIDI clock for you, controlled by MIDI Start and Stop messages.

The MIDI board connects to the circuitry in several places. There are half a dozen wires to connect to locations on the voice and CPU boards to pick up power, clock and run/stop signals. A ribbon cable goes to the CPU board for the voice triggers, where the external triggers connector originally plugged in. MXR actually wired this in parallel with the buttons on the front panel, which means that the sequencer can record notes played in over MIDI.