Introduction

Until I came across one while browsing eBay, the E-drum was not something I even knew existed. It apparently wasn’t very popular, and there isn’t much discussion about it, unlike the rest of the E-mu Systems product line. It’s a fairly simple digital sample player that replays PCM audio, stored on removable cartridges; triggered from a piezo sensor under a rubber mat on the top, or from an external trigger signal.

It turns out it wasn’t really an E-mu product either – it’s a rebadged Clavia DDrum, which was later available as a modular rack system. E-mu apparently licensed the design to try and break into the emerging electronic drums market. As far as I know, the cartridges are compatible between all three (but not the later Clavia Sound Pac type cartridges).

E-Drum Overview

Despite being limited to playing back one-shot PCM samples, the E-Drum is able to produce surprisingly varied and expressive results. The velocity from the piezo sensor is always routed to amplitude, but can also be routed to the sample pitch, adjustable with a knob.

The E-Drum applies a basic envelope to the sound with adjustable decay time, important as the PCM audio on the cartridges is heavily compressed to achieve better signal to noise ratio from the 8-bit linear encoding. It’s also useful to be able to dial in a specific decay time on sounds like toms or cymbals. In addition to this there’s a very effective EQ section, with knobs for bass and treble.

A cartridge can hold one, two or four sounds, depending on the capacity of ROM chip fitted in the cartridge, and how the wire links on the cartridge PCB are configured. The two buttons on the front of the E-Drum set which sound is played, if it’s a multi-sound cartridge.

The last thing worthy of mention is the trigger input jack, which is a TRS (stereo) connector. With a suitable lead wired up, not only can it trigger the sounds with varying amplitude on the tip of the plug, but you can also send in pitch CV on the ring of the plug. I haven’t really explored this much yet though.

Cartridge Clone

The single cartridge mine came with was ROTOTOM 1 – a recording of a rototom, as you might have guessed. A well recorded one too, that really showcases the velocity features of the E-Drum well. Other cartridges were of course available at the time, but are now just as rare as the unit itself.

Needless to say, a clone of the cartridge was on the cards. I desoldered the parts from it, scanned in both sides and traced the original layout, keeping the original hand-drawn wiggly traces more or less as they were. The ‘VER. B’ cartridge board was designed to accommodate a 28-pin EPROM, and had wire links that could be fitted to configure the board in various ways – ROM size, number of sounds, etc.:

Link	Function
0.1, 0.3, 0.6, 1.2, 2.5	Sets sample length in seconds
12, 13, 14	Address lines 12, 13, 14
A, B, E	Left sound select button
C, D	Right sound select button
L	Enables additional pre-EQ filtering if fitted
Rdecay	Resistor – allows the cartridge to trim the range of the decay time control if fitted

Photos