Boss Dr110 Drum Machine Modifications Pt.1 (Or "How I Spent My Spring Break Soldering")

The Boss Dr-110 is a critically under rated analog drum machine (the last?) made by Roland in 1983. It has 6 different drum voices: kick, snare, open and closed hi-hat, cymbal, and clap. Similar in sound to the much more sought after tr-606, I feel that the main reason it is so unknown is probably the awful grid programming interface with an LCD that gives it the appearance of a digital machine. It is also pre-midi and lacking any volume or tone control over the individual voices. Despite this weakness it has been my primary drum machine for the last couple years.

Recently the jack on mine stopped functioning. When I opened it up I discovered that the jack was of a PCB mounted type that I did not want to wait to order a replacement for, and the standard panel mount 1/4" I replaced it with did not fit inside, but had to hang outside the case. This was too much of a hack job for me to let remain, also I figured that if I was going to penetrate my precious machine with a soldering iron, why stop there? It was modification time.

The first mod I performed is an odd one that probably no one else needs, but I have found that it didn't go slow enough for me. Specs say it bottoms out around 50 bpm, but that's probably counting quarter notes and was nowhere near enough to satisfy my taste for dirges and left most of the dial to the territory of rediculous gabber-like speeds. So by looking at the schematics I replaced R34 (150K) with a 500k resistor, and while it's still not as deathly slow as I'd like now most of the tempo dial at least covers a usable range.

The next step was googling the mods made by others. My main sources were vidiotsquad, Dave Magnuson, and Rob from the Analogue Heaven message board. The vidiotsquad post was the best laid out and easiest on the eyes, but contained errors, Dave Magnuson was a bit conservative, and Rob was rather vague, but together I compiled a list of 14 tone mods I wanted to do. This will probably be most similar to the vidiotsquad post, but I think there is enough there that it is worth repeating and adding the value changes I made as well as sounds and my own observations.

All of these mods are very simple conceptually, simply replacing a resistor on the board with a potentiometer of either the same or larger value. In practice it was of moderate difficulty because you had to first desolder each resistor from the very crowded circuit board and I would not recommend it for beginners. I don't think there is room inside the tiny DR-110 case for a single extra pot, so I housed all of them in a radio shack project enclosure I attached to the side with two small machine screws and still had the hardest time closing it back up simply from the size of all the wires.

Kick

These are actually the only two mods that did not satisfy me. I was hoping to get more bass and a longer decay out of it, as some youtube videos suggest is possible. I think I might have damaged a capacitor in a late night soldering session and my next step is to breadboard the circuit and see if I can figure out what went wrong.

pitch: r70 with 1k pot

decay: r86 with 50k pot

Snare

If you like at the schematic you can see that the snare circuit is actually composed of two parts, a "damping oscillator" and a "Swing type VCA" (terms from the service manual.) Actually almost all of the voice circuitry are just these two very simple two building blocks duplicated and rearranged with different component values, with the damping oscillator creating tones and the swing VCA providing metallic ringing and fizzing sounds. What the "snap/fizz mix" mod is doing is providing a volume control for the swing VCA part of the circuit and turning it all the way down is akin to removing the snares from a drum, leaving a melodic tom sound. The "impact pitch" mod provides control over the tom part of the sound, and the decay let's you vary from a very full sound to a click.

snap/fizz mix: r81 with 50k pot

impact pitch: r76 with 50k pot
decay: r84 with 50k pot

Hi-hat

The hi hat and filter mods are actually the ones I found most satisfying. The pitch and filter controls allowed me to reach some very bizarre metallic tones I would normally associate with circuit bent instruments and varying them in real time sounds awesome. Filter sweep your hi hats, it's time for a techno breakdown.

hi hat filter: r12 with 1k pot

hi hat pitch: r10 with 100k pot

open hh decay: r20 with 1M pot

closed hh decay: r53 with 50k pot

Cymbal

Similar to the hi hat mods, the filter sweep is very entertaining and the decay allows for extremely long cymbal washes.

filter: r16 with 1k pot

decay: r44 with 1M pot

Clap

Prior to the modifications the clap was a voice I totally ignored, nice enough but not my style. However, the tune and filter controls allow for some almost snare-like sounds and sweeping the pitch in a running pattern just sounds awesome.

decay: r113 with 100k log pot

 filter: r114 with 50k pot

tune: r115 with 50k pot

Full Kit
And here is the how it sounds all together!

Conclusion and future modification plans

I'm pretty psyched at the the new sounds and performance possibilities that all the tone mods opened up, but it still needs more. Unfortunately the mods do somewhat affect the volume balance of each sound, and where I had originally planned to add individual outputs as a luxury, I now believe it to be a necessity, the kick drum is also still a work in progress. The other mod is more long term, but I want a better way to program it, either trigger inputs or MIDI capability, I just haven't decided which. My main worry is that I will not be able to fit any more wires inside this beast and I would then have to recase, which I do NOT want to do.