Synth: 0berheim Xpander
Review by: Lx Rudis 6/14/95

Summary:  quasi-modular analog synth from the days of the birth of MIDI

Years Made: 1984-1988.  available custom built from oberheim/gibson till
	release of Obmx in 1994
Polyphony: six voices
Multitimbrality: each voice can be assigned to-a)respond monophonically to
	a defined  midi channel 1-16, b) respond monophonically to an incoming
	1v/oct cv+voltage gate or c)mapped alone or with other voices to 
	respond  polyphonically to a defined keyboard range on midi ch 1-16
MIDI:
    Note on/off: yes
    MIDI controllers (aftertouch, CC, etc): entire range of controllers
	accessible, but only 5 input "ports" .  2 of these ports are fixed to
	respond globally to assigned  controllers incoming on the instrument's
	(user assigned) basic midi channel.
    Sysex patch dumping:yes
    Sysex parameter control:yes
Other inputs/external control:
    CV/Gate: yes,six of them-also translates incoming cv/gate data to MIDI
    Clock: yes
    Other CV: two cv "pedal" inputs-ped2 is global.
    Audio:no, but a mod is available for this. check hyperreal
    Proprietary (DCB, etc): originally designed to be driven by the DSX
	sequencer, but MIDI came along and.....
    Programmer: data encoders and switches can send (echo) via MIDI sysex
Outputs: stereo (7 position pan), mono(summed stereo), 
	or six individual outputs
Patch storage: 
	100 single voice programs
	100 multi timbre setups of single voice combos
    Patch dumping (tape, MIDI, etc): good cassette interface,  MIDI dump

Voice architecture:
 	*2 VCO's-triangle,saw,pulse,sync on vco2 
   	noise generator
	*VCF with variations on low,band,notch and hipass response.  
		also 4 "combination" filter modes.
	*4 VCA'swith 2 of them in series after VCF
	*18 (!) "virtual" vca's for data control
 	*5 lfo's with basic waves plus s/h and random functions
 	*3 tracking generators
 	*3 ramp generators
 	*FM of vco2 or vcf by vco1
 	*lag processor(portamento)
	*1 global lfo for mod wheel.

Interface: three giant flourescent green text displays.  six encoder knobs.
  page and  value numbers.  numeric keypad.  the right side of the face
  panel is a printed block diagram of the voice architecture with buttons 
  for each "module".  pushing a button updates displays to emulate block 
  diagram with encoders under displays used to alter patch data.
Sequencer/Arpeggiator: none
Keyboard/rack: neither a rack nor a keyboard be.  this thing looks like it was 
  ripped out of a spaceship's control deck.  about 36" by 15" by 6". 
  slanted case.
Known problems:  some late period Xpanders were tossed together with out of
	spec chips.  they exhibit strange intermittent tuning problems of 
	filters  and vco's.  Instrument is generally quite reliable.
Accessories: Xk MIDI controller-61 key master keyboard
Related synths/gear: Matrix12 is a keyboard version with 2 xpander voice
	boards (12  voices) and updated firmware.  matrix6 is less flexible
	modulation matrix synth.  matrix 6/r and matrix 1000 are rackmounted
	versions of matrix6. matrix modulation and tracking generators live 
	on in the alesis quadrasynth, Kurzweill K2000 and Emu Proteus family.
Price range: as of  6/15/95, $800 to $1800 US...not cheap.
Availability: estimated production run of 2000 units, worldwide
Comments: 
   rich, deep, VERY powerful synth for a variety of styles of music.
 Strengths: multimode filter, sheer programming power..."a soundtrack in a box"
 Weaknesses: bass response not as good as Roland or Moog.   envelopes not
    as "snappy"  as moog's.  less resolution on some  controls (lfo frequency,
    tracking generators) than some of us would like.  programming/editing
    multi-setups can be confusing.  big unusual case.  primitive MIDI cc
    implementation.
 Overall:  i plan on taking mine with me to the afterlife...after having
    spent a few more decades with it on this particular plane of existence!
 Other:  Instrument features hard to find Curtis filters, but it is
    mostly discrete (easy toreplace/repair) components.  almost  anything can
    be controlled by  anything else. apparantly one of Marcus Ryle's first
    synth designs.  Tom Oberheim had  some input on specs and hardware design.



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Lx Rudis                   Eater of Souls              415.882.1730  Voice
lx@fht.com                 Foley Hi-Tech               415.882.1733  Fax
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