Boss DM-2
A compact analog delay that draws a scant 11mA.
Overview
The DM-2 has no tap tempo, no digital readout and no modulation. It is a bucket-brigade delay circuit in a compact Boss enclosure, drawing 11mA at 9V from a single battery or AC adapter. That is a modest draw. BBD delays are hungry circuits, and the DM-2 could run for extended periods on a 9V battery, which made it a practical choice for gigging players.
Input impedance is 470kΩ, which works with guitar pickups without loading them down. Output load impedance is specified at over 10kΩ, so it feeds most amplifier inputs and downstream pedals without complaint. The whole thing weighs 450 grams. That is enough to stay put on a pedalboard and light enough to forget about in a gig bag.
The delay time is set by a single knob, and the maximum delay is short by modern standards. This is a slapback and ambience machine, not a looping tool. The BBD chip is a 4096-stage device. The service documentation notes that Roland periodically changed BBD suppliers to keep up with electronic developments, and serial numbers from 182000 and above got an improved BBD version. The BBD and its driver are incompatible with the older parts, though the PCB assemblies themselves remained interchangeable. Anyone servicing one today needs to know that.
The semiconductor list is all analog staples: 2SK30A(TM)-Y FETs, 2SC945-P and 2SC732TM-GR transistors, RD5.6EB-3 and RD11EB-3 zener diodes, an SLP-135B LED, a µPC4558C dual op-amp, an NE570N compander, and an MN3101 BBD driver paired with the 4096-stage BBD. The NE570N is behind the low noise floor. It compresses the signal going into the BBD and expands it coming out, which masks the noise the bucket brigade adds along the way. The same trick made several classic analog delays usable in professional contexts.
Calibration takes bench work. The service manual specifies a clock frequency check at TP-1 (IC4 pin 4), with VR3 set for T=146µs, which works out to 6.8kHz. There's a clock leakage cancel adjustment at VR2 that requires converging two outputs to minimize the clock component with no input signal present. Distortion is minimized with a separate adjustment, using a 0dBm 200Hz sinewave fed into the input jack, regardless of where the rate control sits. None of this is user-serviceable in any practical sense. It takes an oscilloscope and a signal generator.
Collectors note that the DM-2 occupies an odd position in the Boss lineup. It predates the digital delay revolution that would eventually make analog BBD delays obsolete in the mass market, and it lacks the onboard modulation and longer delay times that later analog designs would add. What it has is a specific, dark, slightly degraded repeat character that digital emulations have spent decades trying to capture. Whether they've succeeded is still debated among players who've owned both.
Construction is standard Boss for the era: a metal enclosure, a hinged battery compartment, and a footswitch built to survive years of stomping. The 450-gram weight is mostly enclosure and hardware, with no heft from a transformer or oversized circuit board. The 11mA current draw means a standard 9V battery will last a reasonable amount of time. Players running the DM-2 on a pedalboard power supply will find it works with most isolated outputs.
The available materials give no documented production end date for the DM-2.
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