Oberheim DMX
Programmable Digital Drum Machine (1981)

Classic American drum machine based on primitive 8-bits samples but great sound: this is the history of eighties music from New Order to Run DMC.

DRUM MACHINE The main panel features a flurescent display, 10 sliders for volumes mixing, 24 buttons for edit and 18 trigger pads with no velocity.

Back panel terminal connectors:
- 12 separate mono analog out
- 2 pedalswitch inputs for start-stop and NEXT pattern
- sync tape interface
- external clock I/O
- switch tab for memory protection
- tape interface
- custom 3 x 4 molex connectors: the 1st molex row is TRIGGER IN and each instruments can be controlled by a simple pulse (range +1-5V).

 

VOICE main CPU based on a Z80 Zilog manages 8 slot-in voice boards; all boards have a trimmer for pitch tuning.

Each voice board contain various 4 kb EPROM model 2732 with companded 8-bits digitalized sounds and some longer sounds (like crash) take a total of 16 kb split in 4 x 2732 EPROM. pitch tuning from trimmer LISTEN

 

BOARD EXPANSION it is also possible to use different sets of boards, many were available at that time or directly burn the EPROM memories with new samples.

some earlier DMX models have a tom board which lacks the famous CEM IC. LISTEN various eprom sounds

PCM SOUND 24 sounds derived from the PCM EPROM combined in various pitches:

- bass drum: loud / medium / soft - crash cymbal - snares: loud / medium / soft - tambourines: loud / soft - hi-hats: close / accent / open - toms: from high to low pitch - shakers: loud / soft - ride cymbals: loud / soft - handclap - rimshot.

CV the second molex labeled "CV IN" changes samples pitches within a 0-6V range.
Some third-part sellers build some early Midi trigger system.

SEQUENCER works in 2 main modes:
- real time with metronome (variable dividers) and correction-quantisation from 1/48 to 1/4 note.
- step by step: just entry pauses or notes between 1/4 value and 1/48.
Other functions for edit like COPY, OVERDUB, ERASE notes/ patterns/ songs/ instruments or variable time signature.

SYNC tempo can be set with internal clock from 25 to 250 BPM or slaved to SYNC TAPE or trigger input pulse at 96 PPQ (not so common).

 

MEMORY is non-volatile:

- 2000 events - 100 sequences - 50 songs. A special board clipped to the Z80 doubles internal memory; this board usually "updates" to OS 3.1 which adds some new sequencer functions. Also a third-part MIDI interface can be added with some hardware modification. early DMX CEM LESS, upgraded to 3.0 OS with extra patterns memory board. Click to enlarge pic

 

 

OS is burnt in 2 eproms:

- DMX 1.0 - DMX 2.21 - DMX 3.20 (for memory EXP) - DMX 4.01 (for midi)

 

 

MAINTENANCE there are 2 common issues out of 2 models I owned:

	- BATTERY: internal rechargeable battery just leaks on the circuits and damage the nearby ICs logics; often the first symptom is troubles with unstable clock frequency. battery leakage repair
	- DISPLAY :often some display modules fail and some gibberish characters appear - found some spare parts on Ebay at *EVIL* price. second module failure! Faulty display module replacement (there are 4)

 

RELATED FAMILY

DX - was the successive economic version of DMX with different sample and a single board for voice samples. Some of the US versions were Midi factory upgraded.

GALLERY:

original advert		m3r artwork 1