Hammond DPM-48
A digital drum machine from the organ company — twenty-two pads, eight outputs, and a RAM cartridge slot that could bite back.
Overview
Hammond is hardly the name that springs to mind when you think about drum machines, but the DPM-48 is the company's serious bid for the rock market — and it's a machine that reviewers at the time found genuinely impressive. The unit is built around 84K of EPROM sample space spread across eleven chips (ten 2764s and a single 2732), which is a fair whack above most of the competition: the Drumulator had 64K, the MXR 52K, and the Oberheim DX 64K, against 124K in the LinnDrum. That extra memory shows up in the generally high quality of the sampled sounds, though whether Hammond actually crammed twenty-two separate full samples into that space was a point of skepticism for at least one reviewer — the arithmetic suggests under 4K per voice, which is a tight squeeze for a decent crash cymbal.
The front panel is where the DPM-48 makes its case for real-time playing. Each of the twenty-two sounds gets its own blue button, so the thing can be played with fingers alone. That's a striking contrast to contemporaries: the MXR had twelve voice buttons, the DX eighteen, and the Drumulator only six with a seventh to switch between conventional and exotic percussion. Behind those buttons sit eight separate output channels — individual faders to separate outs or a stereo or mono mix — plus dedicated 1/4" jacks for metronome, two sets of toms, bass drum, hi-hat, snare, cymbal, perc 1, perc 2, headphones, and the mixes. It's the kind of back panel that earns a machine respect in a studio.
Programming follows the pattern-based logic of the era. Forty-eight patterns can be stored, each holding up to thirty-two events, and patterns assemble into songs. The COUNT and LAST STEP keys, used with the grey numeric keys, set the subdivision of a crotchet — 1/2, 1/3, 1/4, 1/6, 1/8, 1/12, 1/16, 1/24, and 1/32, from a plain quaver up to a demi-semiquaver. Real-time input can be recorded with a metronome click track, and once a pattern is down it can be run through what Hammond calls its "automatic correcting system," quantising the timing to a degree set by the minimum duration programmed into the machine. The metronome level is fixed on the mono or stereo mix, but a separate output is provided.
The DPM-48's distinguishing feature — and its most divisive one — is the recess at the front for RAM cartridges. It was reportedly the only digital drum machine on the market to use that storage medium. The cartridges hold two 5118 CMOS RAMs (1K x 8-bit each), giving just 2K for song storage, which limits the user to accessing three songs at any given time. In the studio that's no problem; on stage, owners would be well-advised to label the cartridges and keep them out of beer mugs. There's also a hard warning attached: changing RAM cartridges in quick succession without powering the unit down first stands a good chance of condemning something to the great Silicon Chippy in the Sky. Hammond's own manual is explicit — turn off the DPM-48 before setting or removing the cartridge, and don't insert it with unnecessary force. A write-protect switch on the RAM pack is there for the sane.
Inside, servicing is straightforward enough, though there are flying leads and ribbon cables to contend with. The processing side lives on a PCB attached to the front panel, where a Z-80 type processor runs the pushbutton keys and LED display; a single 2732 EPROM on the track side appears to hold the firmware. The other main PCB carries the bulk of the sample memory alongside much macho TTL, one MC1408 DAC (8-bit, non-companding), four AN6554s, and four LM13600s. The manual, one reviewer noted, is as silent as a grave about what actually goes on inside the DPM-48's head, so how memory is allocated per sound is impossible to determine.
Sound quality drew qualified praise. The toms were tuned in thirds with a good duration of about 0.4", plenty of membrane bounce, but a halo of quantisation noise that wouldn't be obvious buried in a mix. The lower toms ran about 0.5" with a good solid tone, again on the noisy side — and because the second set runs through a separate D/A channel, two toms from the two groups can be played simultaneously, unlike the LinnDrum and Oberheim DX with their single time-shared tom sample. The reviewer's verdict was that the toms would benefit from being re-recorded at a faster sampling rate at the expense of length.
Build quality is a cut above the budget norm. The nicely solid aluminium front panels and well laid-out, colour-coded buttons work positively, with none of the sloppy feel so often found on equipment manufactured on a tight budget — a pointed contrast to the spartan pressed-steel construction of the Drumulator. The unit is compact at just 13.75" long, 10.4" deep, and 3" at maximum height.
The verdict from Studio Sound (November 1984, p.108) was unambiguous: a superb digital drum machine at a remarkably cheap price, easy to program, with the majority of sounds very good. The reviewer's wish list was a larger-capacity RAM cartridge (using 6116s, for instance) and the option of different EPROM sets to suit different users. Contemporary classifieds put used DPM-48s around £275–£290 in the mid-1980s, and one listing describes the unit as a percussion unit with twenty-two sounds including Simmons chips — a reminder that the DPM-48's voice set could be swapped or supplemented. Whether it broke Hammond into the rock market is another question; the machine's reputation rests on that cartridge slot and those twenty-two playable buttons.
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