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The Kurzweil K250 a.k.a. "Kurzweil 250", "K250" or "K-250", manufactured by Kurzweil Music Systems was the first electronic musical instrument which produced sound derived from sampled sounds burned onto integrated circuits known as read-only memory (ROM), without the requirement for any type of disk drive. Acoustic sounds from brass, percussion, string and woodwind instruments as well as sounds created using waveforms from oscillators were utilized. Primarily designed for the professional musician, it was conceived and invented by Raymond Kurzweil, original founder of Kurzweil Computer Products, Inc., Kurzweil Music Systems and Kurzweil Educational Systems with consultation from Stevie Wonder; Lyle Mays, an American jazz pianist; Alan R. Pearlman, founder of ARP Instruments Inc.; and Robert Moog, inventor of the Moog synthesizer.
- 1 History
- 2 Technical specifications
- 3 Voices
- 4 Software versions
- 5 Manufacturer optional components
- 6 Manufacturer transitional components
- 7 Third party optional components
- 8 Undocumented functions
- 9 Artists and musical groups who have used the Kurzweil K250
- 10 Audio
- 11 Audio and video
- 12 Articles on the Internet
- 13 References
- 14 External links
In the mid-1970s, Raymond Kurzweil invented the first multi-font reading machine for the blind, consisted of the earliest CCD flat-bed scanner and text-to-speech synthesizer. In 1976, Stevie Wonder heard about the demonstration of this new machine on the Today Show, and later he became the user of first production unit, Kurzweil Reading Machine. It was the beginning of a long-term relationship between them.
In 1982 Stevie Wonder invited Raymond Kurzweil to his new studio in Los Angeles, and asked if "we could use the extraordinarily flexible computer control methods on the beautiful sounds of acoustic instruments?" In response to this query, Raymond Kurzweil founded Kurzweil Music Systems, with Stevie Wonder as musical advisor. A prototype of the Kurzweil K250 was manufactured for Stevie Wonder in 1983. It featured Braille buttons along with sliders (potentiometers) for various controls and functions, an extensive choice of acoustic and synthesized sounds to choose from, a sampler to record sounds onto RAM and a music sequencer utilizing battery-backed RAM for compositional purposes. During production of the Kurzweil K250 at least five units were manufactured for Stevie Wonder.
The Kurzweil K250 was officially unveiled to the music industry during the 1984 Summer NAMM trade show. Shortly thereafter the Kurzweil K250 was commercially manufactured until 1990 and was initially available as an 88-key fully weighted keyboard and as an expander unit without keys called the Kurzweil K250 XP. A few years later into production a rack mount version called the Kurzweil K250 RMX a.k.a. K250 X also became available.
The Kurzweil K250 is generally recognized as the first electronic instrument to faithfully reproduce the sounds of an acoustic grand piano. It could play up to 12 notes simultaneously (also known as 12-note polyphony by utilizing individual sounds as well as layered sounds (playing multiple sounds on the same note simultaneously, also known as being multitimbral). Up to that point in time the majority of electronic keyboards utilized synthesized sounds and emulated acoustical instrument sounds created in other electronic instruments using various waveforms produced by oscillators. Five other manufactured digital sampled sound musical instruments were available at that time: E-mu Corporation's E-mu Emulator and E-mu Emulator II; Fairlight Corporation's Fairlight CMI; and New England Digital's Synclavier I and Synclavier II. However, there were major differences between the Kurzweil K250 and these other instruments:
- The acoustic piano sound contained in and produced by the Kurzweil K250 was so realistic tests were conducted with listeners blindfolded to differentiate sonic differences between a 9-foot Steinway grand piano playing and the Kurzweil K250 playing. Both were played through the same high quality $40,000 US dollar sound system. According to Kurzweil, "There was general agreement that it was not possible to tell the difference between the piano and the K250."  This was achieved despite the fact that the sounds in the Kurzweil K250 are 10-bit sampled sounds and utilized a proprietary sound contouring model to reduce memory requirements.
- The Kurzweil K250 could be played as a solo instrument, as an instrument in a band, musical ensemble or in an orchestra. It could also be played as any of these musical groups. Because of this capability, the instrument was one of the first to be used as a Virtual Orchestra.
- Expanding upon this concept a new technology at the time, MIDI Musical Instrument Digital Interface, multiple units and/or other MIDI capable devices could be connected (in a daisy chain fashion) and played together simultaneously or separately. MIDI is utilized to transmit and receive other messaging in controlling other MIDI devices as desired. For example, if twelve Kurzweil K250's were connected together up to 144 notes could be played simultaneously, more than a typical symphony orchestra could typically produce simultaneously with all members playing at any moment.
- SCSI technology is utilized in its system architecture, which was the fastest data transfer technology available at the time.
- It utilized a Motorola 68000 32-bit 10 MHz processor, which was one of the fastest processors available at the time.
- With the sampling option a sound could be sampled up to 50 kHz. (Such a high sampling rate, much higher than the highest frequency humans can hear, is needed because samples of sound at a given rate can represent at best half that audio frequency; see Nyquist frequency.)
- The pitch of a sound could be transposed (see: transposition (music)) up or down using five different transposition modes without much change in timbre, as long as the transposition was not more than a few semitones.
The Kurzweil K250 was highly engineered. For example, the J12 connector on the back of the Kurzweil K250 where the power pod connects to the unit is similar to connectors used in the NASA Space Shuttle. It has hi and low current/voltage rated pins and a lock ring on a collar with a barrel connector. Other details, such as an array of multiple output options, a click track, a sync source (for synchronizing music with another device), an analog output board that produced inaudible noise levels with the widest amplitude (see envelope) available (even at maximum volume), multiple sliders to assign multiple functions, the sampler previously mentioned and a twelve-track sequencer with advanced functionality were all state-of-the-art at the time of production.
The Kurzweil K250 was initially priced at $10,715 plus options (in 1983 U.S. dollars). Memory (Computer data storage) along with costs in designing, engineering, research and development of such a revolutionary product contributed to this cost. Those who could afford the Kurzweil K250 enjoyed a musical composition, MIDI composition and performance instrument unparalleled to any other at the time. An Apple Macintosh computer typically could be connected to the instrument for sound contouring/sound modeling (see Sound synthesis) and musical compositional purposes. Almost 4,000 units were manufactured.
In the latter years of production two related instruments were also manufactured:
- The Kurzweil K225 RMX. The Kurzweil K225 RMX was similar to the Kurzweil K250 RMX and it was more affordable. The Kurzweil K225 RMX contained about half of the sounds available on the Kurzweil K250 and utilized early production Kurzweil K250 hardware. In some cases a sticker identifying the unit as a Kurzweil 225 RMX was used instead of the standard silk screening imprinting.
- The Hyper Kurzweil K250. Very little is known about this model other than the RAM cartridge was relocated to the left front panel, the right front panel possibly had other functionality (unknown), five additional buttons with some sort of SCSI functionality (unknown) were placed above the tuning control, 88 red LED's (Light-emitting diodes) were placed above each key (apparently to light up as the corresponding key was depressed), the manufacturer name KURZWEIL had raised letters instead of imprinted letters on the front panel and the slider caps were different (the slightly rounded edges were squared off). A SCSI hard drive may also have been added below the front right panel area. It is suspected this may have been one of the last Kurzweil K250's developed.
The Kurzweil K250 (with wooden keys manufactured by the Baldwin Piano Company) is heavy and bulky to move; it weighs 95 pounds (plus a few pounds for optional boards and components) and measures 57 inches length x 27 inches width x 9 inches height. The power pod weighs 22 pounds and measures 17¾ inches length x 11⅛ inches width x 4⅛ inches height. The Kurzweil K250 is used today by musicians in recording studios, movie studios, orchestras, ballet/theater companies (see ballet company), colleges/ universities, Bell Labs (the research arm of Alcatel-Lucent), religious organizations, churches and Kurzweil K250 enthusiasts throughout the world.
- 12-track music sequencer, polyphonic, 12,012 events (with version 3 software and higher), fully editable including quantization (see Quantization (music)), section call, sequence chaining, punch-in/out, mute/solo/fader automation, event editing, channel stealing, rhythm change, tempo change, MIDI and tape sync.
- Tempo control, plus or minus up to 700 beats per minute (can be additionally manipulated if using the on-board sequencer), real time.
- Chorus (five different modes – doubling, full chorus, flanging, echo and microtonal) with delay and detuning capability (all editable and adjustable), switchable in real time.
- Transpose (five different modes – octave pitch shift, chromatic pitch shift, octave transpose, chromatic transpose and timbre shift); maximum range of 2 octaves up to 5 octaves down depending upon the mode selected, real time. Note – timbre shift is an application of the technology where the keymap is transposed one way and the pitch is transposed the other way so the pitch stays the same but the digital artifacts are used in the sound.
- Fine Tuning (center position is concert or standardized pitch A=440), real time.
- Brightness (of the sound), real time.
- Sound volume, real time.
- Volume swell, real time (see Expression pedal).
- Tremolo, real time.
- Vibrato, real time.
- Sound velocity, both positive (increase) and negative (known as reverse velocity), real time (see keyboard expression).
- Aliasing, real time.
- Pitch bend, up or down, real time.
- Touch sensitivity, real time.
- Two sustain modes, normal sustain and sustained release (which is a quick dampening of sound after a note is struck), real time.
- 96 non-destructive ROM sounds (basic sound block).
- 341 presets.
- 12 voice polyphony, 12 oscillators per voice, 256 segment amplitude envelope generator.
- 12-bit multitimbral, 16 channels, 144 parts.
- Fully assignable filters and envelopes.
- 2 low-frequency oscillators (LFO's) per voice, 24 multi-form LFO's total, all adjustable, 12 different adjustable options (see Low-frequency oscillation).
- Variable sampling rate.
- 18-bit floating point resolution.
- Truncation, looping (see music loop), velocity crossfading.
- Two separate signal buses (see electrical bus).
- SCSI system architecture.
- Separate outputs on both balanced XLR and 1/4 inch high and low power signal outputs as well as a 1/4 inch headphone jack.
- Click track (built in metronome) for timing purposes, switchable on or off.
- Trigger in via 1/4 inch jack.
- Two full-size brass pedals built into the power pod, used for sustain, sound dampening and sostenuto just like an acoustic piano.
- Full size 88 note velocity-sensitive fully weighted keyboard using lead weights in the keys (excluding RMX models).
- Keyboards can be split, layered or set up with dual-amplitude 6 layers deep. 87 split keyboards in one keyboard setup is possible. Approximately 40 user-created keyboard setups can be programmed, depending upon the keyboard types that are programmed.
- MIDI capable IN, OUT and THRU with limitations on MIDI functionality (not MIDI GM standard – GM standard was implemented in 1991, one year after the Kurzweil K250 ceased to be manufactured).
- Kurzweil K1000 remote mode capable with message display and remote button operation.
- Main unit size = 54" width x 27" length x 9" height.
- Main unit weight = 95 pounds plus a few pounds for optional components.
- Power pod size = 11⅛" width x 17¾" length x 4⅛" height (283 x 451 x 105 mm).
- Power pod weight = 22 pounds (10 kg).
- Power input = 110-120 volts AC, 50/60 Hz, 380 watts (typical, an option was available for 220-240 volts AC). Later units had a different internal power supply and selectable 110/220 volts AC, 50/60 Hz, 380 watts.
- Resident Voices: Concert Grand Piano, Harpsichord, Violin Section, Viola Section, Cello Section, Bass Section, Plucked Acoustic Bass, Snare Drum, Bass Drum, Tom-Tom (2 octave chromatic), Hi-Hat Open, Hi-Hat Closing, Hi-Hat Closed, Crash Cymbals, Ride Cymbals, Guiro, Ratchet, Sleigh Bells, Cowbell, Sandpaper, Hammond tm B-3 Organ (3 settings without percussion, 1 with percussion), Trumpet, Baritone Horn, Valve Trombone, Sine Wave, "Endless Glissando", Nylon-Stringed Acoustic Guitar, Hand Claps, Finger Snaps, Temple Blocks, Grater Up, Grater Down, White Noise
- Sound Block A: Choir, Flute, Electric Bass (open), Electric Bass (slap), Clarinet, Oboe, Harp Arpeggios, Harp Glissando, Conga (open), Conga (slap), Conga (ringing), Chimes, Marimba, Vibes, Timpani
- Sound Block B: Electric Guitar (mutes), Electric Guitar (Lead Strings), Electric Guitar (harmonics), Snare Drums (5 types), Kick Drums (5 types), Hi-Hat Open, Hi-Hat Closed, Hi-Hat Closing, Rim Shot, Claps, Crash Cymbal, Ride Cymbal (rim), Ride Cymbal (Bell), Toms (3 types), Electric Piano (Fender Rhodes tm), Mini Moog tm
- Sound Block C: Solo Violin, Solo Cello, Celeste, Pizzicato Strings, Bassoon, Cathedral Pipe Organ, Hand Bells, Plucked Harp, Sawtooth Wave, Church Pipe Organ
- Sound Block D: Nine Brass instruments
- To determine the software version perform either of the following:
a. Watch the display for the data below while performing a hard reset (power up while simultaneously pressing down the read, list and send buttons).
b. Press F, 1, 1, select, select, 4, select, select. Then read the data on the display.
- ED021485 = Version 2.0
- ED060385 = Version 2.2
- ED011786 = Version 3.0
- ED081586 = Version 3.2
- ED111586 = Version 4.1
- ED082087 = Version 4.2
- ED073087 = Version 5.0
- ED060388 = Version 6.0
- ED051089 = Version 6.1
- ED100389 = Version 6.2
- ED032089 = Version 7.0
- ED070689 = Version 7.1
- ED100489 = Version 7.2
- ED012690 = Version 7.3
Manufacturer optional components
- Sampler: 12-bit sample rate of 5 kHz to 50 kHz, 100 to 10 seconds of sampling time respectively. Six different sampling modes: quick take, de-emphasis, slow decay, normal decay, fast decay and speech. Samples are fully editable. 1MB ROM standard. 1/4 inch microphone input jack for sampling source.
- 2 MB SuperRAM (increases the sampling RAM available from 1 MB to 2 MB).
- 4 MB SuperRAM II (increases the sampling RAM available from 1 MB to 4 MB).
- Sound Block A – a.k.a. "Expanded Basic Sound Block" (adds an additional 88 non-destructive ROM sounds).
- Sound Block B – a.k.a. "Rock Sound Block" (adds an additional 59 non-destructive ROM sounds).
- Sound Block C – a.k.a. "Classical Sound Block" (adds an additional 43 non-destructive ROM sounds).
- Sound Block D – a.k.a. "Brass Sound Block" (adds an additional 35 non-destructive ROM sounds).
- Separate output board (providing twelve 1/4 inch jack discrete monophonic outputs in addition to the polyphonic stereo outputs). See Monophony and Polyphony (instrument).
- Plexiglas sheet music stand.
- Performance (tubular) keyboard stand.
- Volume swell pedal.
- Daughterboard for installing up to two additional ROM sound blocks beyond the capability of adding four sound blocks.
- Kurzweil 250 Quick Load System (QLS)
- For Apple/Macintosh Computers (See: Apple Inc.) – Latest version is version 3.8. Will work with most Apple/Macintosh computers using Macintosh System 6 to Mac OS 9.2 (and possibly later, not verified) for use in uploading/downloading information to/from the Kurzweil K250 and working with that data. Data could also be viewed and/or manipulated using other third party software. A serial interface on the Apple/Macintosh computer is required; on early Apple/Macintosh computers (typical) it is known as a DB-9 connector or Mini-DIN 8 connector (typical) and on later Apple/Macintosh computers it is known as a Geoport, which is a Mini-DIN 9 connector. Some early Geoports using Mac OS 7.5.3 or earlier may not work with the Apple-supplied hardware driver – a driver that is known to work is the Opcode Open Music System 2.3.8 SerialDMA driver (freeware) available at:  If the Apple/Macintosh does not natively contain a DB-9 connector or Mini-DIN 8 connector or Geoport an adapter will be required for interfacing the K250 to the Macintosh—the only known third-party adapter is available at the GeeThree Stealth Serial Port adapter website: 
- For IBM PC compatible personal computers (PC's) – See Third Party Optional Components below.
- QLS cable for connecting the Apple/Macintosh DB-9 or Mini-DIN 8 (typical) or Geoport port to the Kurzweil DB-37 computer jack (DB-9 Male or Mini-DIN 8 Male or Geoport Male to DB-37 Male) -or- the PC DB-9 to the Kurzweil DB-37 computer jack (DB-9 male to DB-37 male).
- QLS Modem Board (SCSI Board) – Apple/Macintosh or PC computer interface for saving/loading of samples, setups, keyboards, sequences and bins using QLS or MacAttach software (predecessor to QLS software for Apple/Macintosh).
- Battery-operated 256 KB RAM cartridge and optional cartridge adapter kit for data storage and retrieval. (Note: Kurzweil indicated a cartridge kit is required, however it has been verified by the author of this article that the cartridge kit is not required if care is taken while inserting and removing cartridges to/from the cartridge slot).
Manufacturer transitional components
During the manufacturing of the Kurzweil K250 several improvements were made to the instrument as updates and upgrades. In addition, third-party components were also available. For those who purchased the instrument later in the manufacturing run, expanded, improved and upgraded components as well as software updates were typically installed in the instrument (unless the instrument was older stock and was not upgraded for some reason). For those who did not have a particular expanded, improved or upgraded component and/or software update and desired it, the item needed to be purchased and if necessary, installation charges were added, either by Kurzweil or by a third-party vendor. The following items are:
- Software ROM upgrades. From the very early instruments to software version 4.X, then software version 5.X, then software version 6.X. and lastly software version 7.X with version 7.3 being the last version produced in 1990. These upgrades offered improved hardware and software functionality, signal processing improvements, bug fixes, maintenance improvements, feature additions/enhancements and increased reliability.
- Hardware upgrades. The CGP (ROM) board was modified to allow additional ROM blocks and the processor board was modified for improved signal processing. The upgraded hardware was typically found in Kurzweil K250's manufactured in 1986 or later and was a highly recommended upgrade for older Kurzweil K250 units being upgraded to use version 5.X, 6.X or 7.X software.
- Power pod upgrades. Revised the type of power supply used and allowed for 110/220 volt AC selectable input.
- Front panel button slider and button design and shape.
- Front panel button labeling changes to match major software enhancements from software version 3.X to 4.X and later.
- Complete Parallel SCSI Type 1 implementation in versions 7.0 through 7.3. A 50-pin Narrow SCSI board was added above the CGP Processor Board. The K250 could then theoretically provide direct connectivity up to eight other SCSI devices (for example to connect directly to a hard drive without the need for a separate computer).
Today either the end user has to install components themselves or a third-party vendor will need to install components since Kurzweil Music Systems no longer provides service or support for this instrument series.
Third party optional components
- Apple II computer or nearly any compact Macintosh computer (Macintosh 512 up to Macintosh IIci) computer using Mac OS version 6 (documented). A later model Macintosh with the proper interfacing hardware (GeoPort) and Mac OS 7 – 9.2 (and perhaps later OS's) has been proven to work.
- MacAttach software for use in uploading/downloading information to/from the K250 using an Apple/Macintosh computer through Kurzweil software version 5.0 (this was superseded by QLS, which was available optionally by Kurzweil Music Systems).
- Sweetwater Sound Block SW800 – a.k.a. "Sweetwater Orchestral Sound Block" (adds an additional 54 non-destructive ROM sounds).
- Sweetwater Sound Block SW900 – a.k.a. "Sweetwater Contemporary Sound Block" (adds an additional 52 non-destructive ROM sounds).
- Various sampled sounds were available via the "Sweetwater network" that Sweetwater Sound established in the mid to late 1980s for the purpose of creating and swapping user-created sounds. Some of those sounds were incorporated on the Sweetwater SW800 and SW900 Sound Blocks.
- Sweetwater Sound K250 Editor Librarian software. Required QLS and a separate MIDI interface from the K250 to the Apple/Macintosh computer.
- Kurzweil Quick Load System (QLS) for PC's – (Note: Information about the following is not well known to the author of this article.) Latest known version is version 1.0 and it is not known if a later version was made for the PC. It is interesting to note Kurzweil Music Systems did not create QLS for the PC even though their name is on the label of the QLS 5¼" floppy disk. (It is not known to the author of this article the company that created QLS for the PC). It is not definitively known which PC platforms or operating systems this will operate on, even though it is suspected it will work on 286 and 386 computers using some early form of DOS. Like the Apple/Macintosh version it is used for uploading/downloading information to/from the Kurzweil K250 and working with that data. Data could also be viewed and/or manipulated using other third party software. A DB-9 serial interface on the PC is required.
- Mono pressure – The User's Guide and Reference Manual indicates this feature is not available. However if the Kurzweil K250 is connected to a MIDI device not utilizing the Rock/Pop General MIDI standard (such as a real church organ) this function can control the volume of that MIDI device independently of any other MIDI device connected utilizing the Rock/Pop General MIDI standard. This feature has been verified to work with Kurzweil 250 software version 6 by the author of this article.
- Channel stealing – If the parameters for "Steal Ahead with Sustain" (Function 10 -> STL4) and "Steal Ahead without Sustain" (Function 10 -> STL5) are both set to 11 apiece it is possible for the Kurzweil K250 to produce more than 12 notes simultaneously with certain keyboard sounds despite the fact there are only twelve analog channels available. This feature has been verified to work with Kurzweil K250 software versions 5 and 6 by the author of this article.
- Sequence chaining (natural, not silenced) using the on board sequencer without inserting a note release on the initiating sequence before chaining to the next sequence – This is very useful if chaining sequences which require note(s) to be held over from one sequence to another:
- If the sequence being chained to contains a note release event corresponding to the note attack on the same track.
- The track number utilized must be the same on both sequences.
- Both tracks utilized must use the same keyboard setup during the period of time involved (the keyboard setup can change after the note release event).
- Note: If utilizing MIDI OUT on the tracks involved undesired consequences may occur on the MIDI device connected as that device may not process the note release. This is because the MIDI device may not see a note release at the end of the first sequence involved possibly resulting in a hung note that may need to be reset manually. Some MIDI devices are able to accommodate this arrangement and others are not. It is possible to overcome this problem by utilizing this feature only for tracks not requiring MIDI and then if MIDI is required duplicate the track for MIDI only and insert a note release at the end of the first sequence (even though this may not produce a satisfactory result). This feature has been verified to work with Kurzweil 250 software versions 4, 5 and 6 by the author of this article.
Artists and musical groups who have used the Kurzweil K250
Reference: Kurzweil 250 User's Guide, Pages 140 – 148 Appendix C: The Kurzweil 250 In the Real World Copyright 1988 Kurzweil Music Systems Incorporated
- 2nd Chapter of Acts, band
- Alan O'Day, singer, songwriter
- Anne Murray, singer
- Anthony J. Resta, producer, musician, composer
- Arlo Guthrie, singer
- Art of Noise, band
- Barbara Mandrell, singer
- Barry White, record producer, songwriter, singer
- Bob Seger, musician
- Bruce Springsteen, musician, singer, songwriter, mentioned in the book "Bruce," a Springsteen Biography, by Peter Ames Carlinwas, used in the recording of the Tunnel of Love Album in 1987.
- Chicago, band
- Chick Corea, jazz pianist/keyboardist, composer
- Christopher Yavelow, composer
- David Foster, composer, musician and record producer – K250 provided signature staccato violin sound on Love Theme from St. Elmo's Fire
- Dolly Parton, singer, songwriter, composer, author, actress, philanthropist
- Dominic Frontiere, composer, arranger and jazz accordionist
- Don Dorsey, audio production consultant
- Doug Ingle, organist, vocalist, composer
- Dudley Moore, actor, comedian, musician
- Eddie Van Halen, guitarist, keyboardist, songwriter, producer
- Emerson, Lake & Powell, band
- Eric Clapton, Singer, songwriter, composer, guitarist
- Flood (Marc Ellis), alternative rock and post-punk producer
- Gabriel Yared, composer - ( '37°2 le matin [Betty Blue]' - K250 extensively used for OST 'Flagrant désir [Trade Secrets]'  )
- George Benson, musician
- Grateful Dead, band
- Herbie Hancock, jazz pianist and composer
- Huey Lewis and the News, band
- Isao Tomita, composer
- James Horner, composer
- Jeff Bova, arranger, composer, keyboardist and record producer
- Jim Steinman, composer, record producer, lyricist
- John Williams, composer, conductor and pianist
- Journey, band
- Keith Emerson, keyboardist, composer
- Kenny Rogers, singer, photographer, songwriter, producer, actor
- Kitaro, composer, multi-instrumentalist
- Lee Greenwood, singer, songwriter
- Lionel Richie, singer, songwriter, record producer, actor
- Lyle Mays, jazz pianist
- Michael Kamen, composer
- Mickey Newbury, singer, songwriter
- Neil Diamond, singer, songwriter, actor
- Nile Rodgers, composer, arranger, guitarist, music producer
- Olivia Newton-John, singer, songwriter, actress
- Our Lady Peace, band
- Pat Metheny, jazz guitarist and composer
- Patrick Moraz, progressive Rock keyboardist
- Paul Shaffer, Music Director of the CBS Orchestra on Late Show with David Letterman
- Prince, musician
- Ray Ellis, record producer, arranger and conductor
- Ray Sharpe, composer, musician and record producer
- Ray Stevens, musician
- Richard Carpenter, composer, musician
- Richard Robbins, composer
- Simple Minds, band
- Spandau Ballet, band
- Stanley Jordan, jazz guitarist
- Steve Johannessen, keyboardist, Singer
- Steve Levine, record producer
- Stevie Wonder, musician and composer
- Stewart Copeland, musician, drummer
- The Judds, mother/daughter duo
- Tori Amos, singer, songwriter, record producer, pianist
- Ultravox, band
- Vangelis, composer
- Wax, band
- Matthias Vogt, scientist, composer
- "All I Ask of You" – from: Phantom of the Opera composed by: Andrew Lloyd Webber – performed by Christopher McGilton and Nancy Smith using the Kurzweil 250 solely as the accompaniment 
- "Gesù bambino" composed by: Pietro A. Yon – performed by Christopher McGilton and Nancy Smith using the Kurzweil 250 solely as the accompaniment 
- Christopher Yavelow – Countdown (For the Nuclear Age) – The Worlds First Computer Opera, completely synchronized from the baton of the conductor to the Kurzweil K250 
- Christopher McGilton – Religious/Sacred Music in .mp3 format performed on the Kurzweil 250 and Yamaha MU-50/80 Sound Module  or 
- Craig D. Tollis – The Happy Frog: Kurzweil K250 – Two demo recordings of the Kurzweil 250 
- Jane Brockman – Kurzweil Etudes excerpts in the tradition of Chopin performed on the Kurzweil 250, in three series:
- Pamela J. Marshall – Spindrift Recordings – Noises, Sounds & Strange Airs, "Child's Play"
- Pauline Oliveros – Dear. John: A Canon on the Name of Cage 
- Steven Johannessen – K250 Demo Music Showcase at the Middle Of Nowhere 
- The Kurzweil 250 Rock Block – Play the 45 RPM Kurzweil 250 Demo Record virtually! 
- The Kurzweil Rocks! – Play the 45 RPM Kurzweil 250 Demo Record virtually!
- The Virtual Kurzweil 250 Sound Sheet – Play the 45 RPM Kurzweil 250 Demo Record virtually!
- Philipp Koltsov – Russian composer & pianist plays Kurzweil 250's patch #1 Grandpiano Demo 
Audio and video
- ASJ Avantius – Muzika u domaćoj kinematografiji ( II DEO ) 
- Bach's Nightmare: The Ultimate Rape, or The Art of Kitsch 
- CBS News Interview With Joel Spiegelman in September, 1988 on New Age Bach and the Kurzweil 250 
- Chick Corea Electrik Band – The Dragon – (Note the Kurzweil 250 is to Chick's left on the bottom and string sounds are played on it during the performance) 
- Christopher McGilton – Magnificat performed on the Kurzweil 250 and Yamaha MU-80 Sound Module – 
- Christopher McGilton – No Greater Love performed on the Kurzweil 250 and Yamaha MU-80 Sound Module – 
- Clinton S. Clark – Film Scoring Portfolio 
- FX – Kevin Loch at Lisner Auditorium Nov. 8, 1986 
- Joel Spiegelman Interview on the Joe Franklin Show, August 1988 
- Keith Emerson – Emerson, Lake and Powell with Paul Shaffer and the CBS Orchestra on the Late Show with David Letterman (Note that two Kurzweil K250's are being played live – one by Keith Emerson and the other by Paul Shaffer) 
- Kurzweil – It all started with Ray Kurzweil – The story of Stevie Wonder's technical challenge to Ray Kurzweil that ultimately motivates the inception of Kurzweil Music Systems. 
- Kurzweil 250 Demo Cassette (Jazz / Orchestral demo from a great sampler-synth) 
- Kurzweil 250 Demo Cassette (With voiceover explaining history and features) 
- Kurzweil 250 Rock Block Demo 33 1/3 RPM Record 
- Mutabaruka – The Mystery Unfolds 
- Pat Metheny Group – Daulton Lee (Information in Italian) 
- Ray Kurzweil – Ray Kurzweil Appearing on Worldnet – Demonstration of the Kurzweil 250 
- Robert Estrin – Piano Questions: A Great Digital Piano – The Kurzweil K250 
- Santino Famulari – La Campanella on a Kurzweil 250 – 
- Steven Johannessen – Visual Music Showcase at the Middle Of Nowhere 
- The Big Cruise – Don Lampasone (ASCAP) 
- The Mosquito 
- Wayne Shorter Quartet – The Last Silk Hat (North Sea Jazz 1986) 
Articles on the Internet
- Sound on Sound – Size Does Matter Kurzweil K250 Workstation Keyboard (Retro) 
- Sound on Sound – Synth Secrets 
- Biography of Ray Kurzweil 
- Additional Article of Ray Kurzweil with picture of Stevie Wonder 
- The Age of Spiritual Machines  or 
- The Man and the Machine:An Interview With Ray Kurzweil 
- Time Magazine – Can We Talk? An article about Speech-to-Text recognition and about the Kurzweil 250 
- Virtual Organ – Virtual Instruments:Joe Barron, Present at the 1984 NAMM Show when the Kurzweil 250 was introduced: 
- What's New In Electronic Music; The Art Advances At Warp Drive: A. Arnold Anderson, New York Times 
- Synthony's Synth & MIDI Museum 
- Mastering the Kurzweil 250, Volume One: User's Guide and Volume Two: Reference Manual, Copyright 1988 Kurzweil Music Systems, Inc. 
- Synrise – Brief information on the Kurzweil 250 (In German) 
- Byrd, Donald, & Yavelow, Christopher (1986). The Kurzweil 250 Digital Synthesizer. Computer Music Journal 10, no. 1, pp. 64–86.
- "A Biography of Ray Kurzweil". Kurzweil Technologies, Inc. 2008.
- The Age of Spiritual Machines (Viking, 1999)
- Kurzweil, Ray. 1984. "The Goals of the Kurzweil 250." Waltham, MA: Kurzweil Music Systems