Oberheim XK/XK-1 MIDI controller

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Last Update 06-27-2019

Features
Not a "master controller"
Caveat Emptor
Firmware Revision
Factory Reset
Epilogue

I generally steer clear of early MIDI accessories.  The MIDI standard was introduced in 1983, and many MIDI implementations from the early days were either misinterpreted (IE the infamous "All Notes Off" on Roland keyboards and Yamaha DX-7 maximum velocity response less than 127) or not implemented in the spirit of "universal control".  The Oberheim XK was introduced in 1985 and falls under the latter.  While it is a MIDI controller, Oberheim chose to optimize it for their Xpander and Matrix-12 products as will be explained later.  Its MIDI implementation doesn't fit the definition of a "universal controller".  The XK does not implement MIDI features added to the standard later, such as NRPNs or 14 bit controller messages.

By the way, while the rear panel badge identifies the model as the Oberheim XK-1 it has zero relevance with the Hammond XK-1.

In the 80s rock band I am playing in, the Andromeda gets a lot of use and its own 61 note keyboard is often not enough with all the sounds I have to play.  To remedy that, my Hammond XK3 in my offsite rig doubles as a MIDI controller for my Alesis Andromeda when I am not playing organ parts.  Since I am using my Kurzweil MIDIBoard as a master MIDI controller for the entire system, I only need note-on & note-off MIDI messages from the XK3 to trigger the Andromeda.  All other MIDI messages are filtered using my JL Cooper MSB+ to keep the system glitch free, which can happen too easily in a complex MIDI matrix system!  Since my stage rig is a compact duplicate of my studio system, I do my sound design development in my studio carrying only my Andromeda instead of the entire stage rig.  This saves a lot of time and a lot of stair climbing to my basement studio.  I sought a good 61 note MIDI controller for my studio to emulate the dual function of my XK3 so I could configure Andromeda mixes for the stage.  None of the modern MIDI controllers met my needs (to be frank, most of them are cheap plastic toys).  I became aware of the Oberheim XK MIDI controller only recently - after a review of its capabilities I decided this would fit my needs.

Features

The XK is a ruggedly built controller with non-weighted 61 note long fulcrum keybed that features attack AND release velocity, and mono aftertouch. While owners have complained about the XK's unreliable Panasonic keybed like that in the OB8 (as well as Moog Memorymoog, Korg Poly-6, others), mine does NOT have the Panasonic keybed - perhaps Oberheim changed to a better keybed in its later years?  The keybed feels like the same one in my Oberheim Matrix-6, and even though it is non-weighted I like its feel better than a lot of other keyboards.  Like the Matrix-6 and Matrix-1000, the XK was imported from Asia and is not an Oberheim design.  The XK features the Oberheim "levers" for pitch bend and modulation, a slidepot controller right above them, and octave shift buttons conveniently above those controls.  Like the OBX/OBSX/OBXa/OB8, it includes HOLD and CHORD functions (handy for a MIDI controller).  The unit weighs 15 pounds and is a low profile case - I could easily add a couple of straplocks and use this as a "keytar".  On the rear panel are jacks for footswitch and external clock.

100 user patches (known as "master programs") can be configured in the XK, with each patch capable of three MIDI zones that can be split or layered.  The XK has a "block copy" that allows you to define a "default" user patch configuration then copy it to a block of patches (this eliminates copying your default parameters to every patch by hand).  MIDI Parameters for each zone include channel number, patch number, multipatch number, upper limit, lower limit, voice limit, transpose, slidepot CC#, mod lever reverse CC#, switch# for footswitch, mono mode (not "unison"), levers on/off, aftertouch on/off, velocity sensitivity, and arpeggiator.  Velocity sensitivity is offered in two curves (only one is really useful), plus fixed velocity.  Release velocity uses the same sensitivity selection. Patch numbers are only assignable from 0 to 99 (not the MIDI max of 127), and Pitch bend and aftertouch CC# are fixed and cannot be reassigned.  Pitch bend resolution is only 9 bits not 14 as the MIDI spec permits.

The arpeggiator can be set to one zone at a time and can be externally clocked from the rear panel jack but its maximum rate is 40hz (reduced to 20hz in OS version 1.4, see below).  The arpeggiator can be combined with the HOLD function, which latches the notes so you don't have to hold them down.  The CHORD function can also be used to arpeggiate a chord using a single key press.  Arpeggiator intervals are "global" and are not stored with a user program.  Multipatch number is only useful with the Oberheim Xpander/Matrix-12 products.

START, CONTINUE, STOP, AUTOTUNE, and ALL NOTES OFF MIDI controls are available but not as dedicated buttons thus they require a two button press.  Song Select is available, again requiring two button press and is not programmable.  Aftertouch sensitivity can be adjusted, the value is global and is retained with power off.

Spillover is possible on the XK using the voice limit parameter.  When the parameter is set to a value other than 16, the XK will transmit note messages for the first Nth notes, then each succeeding note is transmitted on the next adjacent MIDI channel.  This was optimized for the multipatch feature of Oberheim products like the Xpander/Matrix-12 but is not useful for other products.  This is what I mean when the XK is not optimal as a "universal controller".  Unfortunately there is no facility in the XK to configure patch numbers for the other MIDI channel.  If you perform the factory reset procedure, the default patches have zones programmed to odd numbered MIDI channels.  This is to ensure that a spillover operation does not cross into another zone.

"Mono mode" begs some clarification.  This does not turn the XK into a monophonic controller.  What it does is implement Mode 4 of the MIDI specification.  The usual operation of a zone is to transmit MIDI notes on the same MIDI channel (barring the spillover option).  MIDI Mode 4 transmits each succeeding key press to the next adjacent MIDI channel.  On the XK the voice limit forces the channel to "roll over" when the number of voices is exceeded.  This is intended to operate as a multitimbral system, where each MIDI channel can have a different sound called up.  Of course this requires an adequate set of MIDI devices for the receiving end, or MIDI devices capable of multitimbrality.  Since the XK modulation controls (pitch bend, mod wheel, slidepot, aftertouch) are mono only, every MIDI channel gets the same modulation amounts.  Unfortunately there is no facility in the XK to configure patch numbers for the other MIDI channels. top

Not a "master controller"

In my assessment, the Oberheim XK does not fit the definition of a master MIDI controller.  Its feature set for configuring a MIDI setup is pretty shallow.  Missing parameters for a master MIDI  controller are setting preset volume, modulation depth, and other MIDI parameters such as filter cutoff and envelope generator transient times.  The lack of ability to reassign aftertouch to a different MIDI CC#, missing ability to configure patch numbers for "spillover" operations, and no SYSEX patch archiving are big problems.  I may be spoiled by my MIDIBoard, but it did teach me parameters that are valuable for a master controller.

I have to say I am not a fan of slidepots for modulation controls.  Slidepots have a short life, and finding a replacement slidepot is hard because the pins have to line up with the footprint on the PC board (there is no industry standard).  I am very tempted to modify my XK to use a control other than the slidepot. top

Caveat Emptor

I have two very big beefs with the XK:
  1. NO PATCH ARCHIVING!  Only a MIDI output is provided and there is no SYSEX patch data transmission/reception implemented.  There isn't even a tape interface for archiving patches.  You must record your configurations on pen and paper, and the owners manual failed to provide a blank user patch template.  In my book, this is a stupid omission!
  2. WALL WART I DESPISE wall wart power supplies with the non-locking plug as they slip out too easy.  Wall warts are too fragile for the harsh rigors of gigging, and are a PITA to pack up.  Since I am a gigging musician, I refuse to use wall warts in my stage rig.  This means the XK is delegated to studio use only. top

Firmware revisions

Firmware rev 1.4 adds some features:
  1. The HOLD/CHORD functions are separate per zone
  2. The action of the pitch bend can be reversed (I greatly preferred the reverse orientation where pulling the lever towards you is bend down)
  3. Arpeggiator gate time is changed to minimize missing or sticking MIDI notes with fast tempos.  It also reduces the maximum tempo from 40hz to 20hz.
  4. Modulation lever (pulled toward player) CC# can be reassigned but is global.
  5. Velocity curves can have a maximum velocity value to accommodate the Yamaha DX-7 and other keyboards whose maximum velocity response is less than MIDI velocity=127.
There is no way to tell what version is in the XK other than attempting the new features or opening the hood to inspect the marking on the EPROM chip that holds the firmware. top

Factory Reset

If you acquire a used XK you should perform a factory reset procedure:
  1. turn off power
  2. press & hold MASTER PROGRAM button
  3. turn on power
  4. press STORE
  5. two "_" characters will appear in the display
  6. press "9" twice
  7. display will count down from 99, resetting all user patches in memory.
  8. No undo is possible, so archive your patches before a reset. top

Epilogue

While it is an adequate MIDI controller, don't use the XK as a master MIDI controller as its feature set is rudimentary and it lacks some crucial features.  Lack of SYSEX patch archiving is a serious omission that takes it out of the running for a master controller.  Since this product uses a coin battery on the circuit board to retain user patches when power is off, these batteries are due for replacement as they are over thirty years old and can cause potentially irreversible damage to the circuit board if the battery leaks.  If you acquire one of these, take it to a competent tech right away to replace the battery (this is not a job for the novice, and the procedure is not expensive for a tech).  On the plus side, a numeric keypad is provided for data entry - I abhor interfaces with only increment/decrement buttons for adjusting data.  If you have an analog synthesizer module with MIDI, the XK is a good controller. top

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