Product History

Tom Oberheim
Guess what! I did not design by myself all the products described in this section of my website - I HAD HELP!

So, I dedicate the following section to all the creative, hard-working engineers, technicians, and support people that have helped me so much over the years at my three companies.

Thanks gals and guys!

Tom Oberheim


Music Modulator & RM-1

The first commercial product that Tom produced was the Music Modulator which was the result of combining Tom's experiments with ring modulators with other circuitry to create a device that could be used in live performance. This product was used by a number of contemporary musicians including innovative trumpeter Don Ellis, and experimental composer Richard Grayson, who played the units with Tom in improvised live performance concerts. Tom was asked by the acclaimed film composer Leonard Rosenman to provide a ring modulator for an upcoming movie Beneath the Planet of the Apes (1970). 

The Music Modulator was also sold by the Chicago Musical Instrument Company (later Norlin Corporation) under the Maestro name as the RM-1.


Maestro PS-1 Phase Shifter

Tom became interested in the sound of the Leslie rotating speaker which was starting to be used in pop songs as more than just an organ speaker. His experimentation led him to "phase shift" circuits that at first did not do an accurate simulation of the Leslies but allowed creation of some interesting sound-modifications. He designed a product that created this effect which became known as the Maestro PS-1 Phase Shifter. The device was one of the first phasor devices on the market and became one of Oberheim’s best-selling products. The device used a 6-stage phasor design.


Digital Sequencer (DS-2A)

Using a combination of what Tom had learned about analog synthesizers by becoming an ARP dealer in the Los Angeles area in the early 1970s and his 10 years as a digital systems engineer, Tom designed the DS-2A digital sequencer that would allow the musician to enter a musical sequence of notes and durations directly from the synthesizer keyboard. The 144 step sequencer interfaced with the most of the analog synthesizers available at the time including the ARP 2600, Odyssey, and the Minimoog.   Three transposition settings could be preset and recalled. Each note in a sequence could have a duration from 1/20 of a second up to 8 seconds.


Synthesizer Expander Module (SEM-1)

As a consequence of the success of the DS-2A Tom decided to produce a small analog synthesizer module to be used in conjunction with the sequencer. It was designed so that it could also be used to enhance the sound possibilities of the ARP & Moog products by means of its multi-mode filter. The Synthesizer Expander Module is a complete, classic analog synthesizer implemented with two precision voltage controlled oscillators (VCOs), a wide-range 2-pole multi-mode filter (VCF), two envelope generators and a low frequency oscillator (LFO). Included within the module design are selectable modulation sources for modulating the VCOs and the VCF. Internal connections can be applied to panel jacks in to allow integration of the module with external equipment.


Universal Synthesizer System (USS-1)

The USS-1 was not a synthesizer, but one of the first multi-effects devices. The USS-1 included the following sound modification features: a unique fuzz circuit, a voltage controlled synthesizer-type filter, sample/hold, an envelope follower, a PS-1A phase shifter, and an octave divider all in one box. The unit was used extensively by guitarist Wah Wah Watson for Herbie Hancock’s mid-70’s fusion albums, among others.



The Phasor pedal was a smaller version of the PS-1A circuit with a single knob for speed control instead of the three rocker switches from the earlier design. It utilized a 4-stage phasor design. It was also released under the Maestro name as the Mini-Phase.


Voltage Controlled Filter

The Voltage Controlled Filter pedal was an SEM-type VCF filter circuit coupled with an envelope follower and a sample/ hold circuit. This product was also released under the Maestro brand as the Maestro Filter Sample/Hold.


Four Voice Polyphonic Synthesizer

The Oberheim Four Voice was the first commercially available polyphonic synthesizer. By utilizing multiple SEMs and a digital scanning keyboard, this instrument allowed the musician to play up to four keys at a time, where each key controlled a complete, true analog synthesizer. Each voice was completely independent and could be programmed to have the same setting or different settings, which allowed creation of massive, realistic orchestral sounds.

The assignment of key depressions to SEM voices was controlled by selecting different modes in the keyboard electronics section of the instrument. This allowed both polyphonic operation, as well as having all SEMs play together in unison. Another unique feature of the keyboard electronics was the ability to select true, polyphonic portamento. To enhance the musician's ability to change the overall sound of the instrument, the patented Polyphonic Synthesizer Programmer was also available. Additional features included the ability to control the output level and left-to-right panning of each SEM in order to create a powerful stereo sound field, and cassette interface for storing different settings.


Two Voice Polyphonic Synthesizer

The Oberheim Two Voice synthesizer was created as a performance keyboard instrument by utilizing two Synthesizer Expander Modules and a classic analog sequencer, coupled to a 37-note keyboard. The inclusion of two SEMs and a two-voice capable sequencer allowed the instrument to be used in three operational modes:
-  2-voice polyphonic keyboard mode
-  2-voice sequencer mode
-  one SEM & one sequencer track mode
The third mode allowed a sequencer track to play one SEM with the second SEM could be played from the keyboard. Also, the keyboard could be used to transpose one or both sequencer tracks. Modulation sources included two envelope generators, two LFOs, and noise generator and a sample/hold circuit.


Eight Voice Polyphonic Synthesizer

Why stop at only four voices? The programmer module in the Four Voice was designed to control up to eight SEMs, so an extension cabinet with four more SEMs was created. When the two cabinets were connected together an eight voice was formed. The Eight Voice was one of the most powerful synthesizers of its era.


Eight Voice Dual Manual

A limited number of special version Eight Voice synthesizers was made that featured two keyboards. The bottom keyboard was extended to five octaves, while the upper keyboard was four octaves, the same size as in the standard Four Voice and Eight Voice models.



The Oberheim OB-1 monophonic synthesizer was Oberheim's first completely programmable analog synthesizer. The OB-1 could store eight onboard patches with touch-sensitive buttons and interfaced with a cassette interface for external storage. Based on the SEM, the instrument added ADSR envelopes, a noise generator, and a switchable 2 pole/ 4 pole VCF with keyboard tracking.



The OB-X was the first polyphonic, fully programmable Oberheim synthesizer. The instrument was available in 4-, 6-, & 8-voice versions and was based on SEM circuitry. The instrument retained polyphonic portamento from the 4-voice.and added polyphonic sample/hold, included an enhanced LFO, unison chord/hold feature, cross-modulation, as well as stereo and mono outputs. Paddle pitch and modulation levers were introduced on the OB-X.
A cassette interface was built-in for saving preset sounds to tape.



The OB-SX was a smaller, preset-based version of the OB-X. It was available in four, five, or six voice configurations, and originally featured 24 presets and had black/gray/white front panel graphics similar to the OB-X. Later units were equipped with 56 presets and were cosmetically upgraded to contain blue-line graphics similar to the OB-Xa.



The OB-Xa was the successor to the OB-X and represented a major change in the internal voice circuitry as well as its external look, being the first Oberheim synth to feature the now-iconic blue lines on the panel. While the circuitry in the OB-X was based on the classic SEM design, the OB-Xa voice circuitry was based on the Curtis family of synthesizer chips. In addition to adding increased reliability and serviceability, a 4-pole filter was added. Available in 4, 6, and 8-voice versions, most OB-Xa units contained 8 voices in order to take full advantage of its new programmable split and layer bi-timbral capabilities. Originally shipping with 32 preset memory locations, later OB-Xa models were expanded to feature 120 programs.



The DMX was a programmable, sample-based digital drum machine. The DMX shipped in the fall of 1981 with eight independent drum voices each containing up to three sounds, for a total of 24 drum sounds triggerable from the front panel buttons. Each voice could be individually tuned, mixed via faders, and had a direct audio output on the rear panel. Each voice was contained on its own dedicated voice card, which could be swapped out by the user with alternative drum voice cards that were sold separately. The DMX could record, save, and edit sequences and songs stored in internal battery backed-up memory, with a maximum sequence time of over 5 hours and up to 2000 events. It could also quantize and add rhythm humanizations like shuffles, flams, and rolls.



The DSX was a 16-voice polyphonic digital sequencer designed for integration within the Oberheim System. Capable of storing 10 10-track sequences with 6,000 steps, the DSX was a powerful digital sequencer for its time and expanded the functionality of the Oberheim line. Introduced before the existence of MIDI, the DSX could be connected to an OB-X (later models), OB-Xa, OB-SX, or OB-8 (introduced later) via a 37-pin computer interface cable. In addition to the eight voices of the connected OB synth the DSX could control up to eight additional voices via dedicated CV and Gate outputs. The DSX was the first real-time sequencer with quantizing capability, and when synchronized with a DMX (via a 1/4" cable) and an OB synth became the heart of “The System” which spawned many hit records in the ‘80s.



The DX was released in 1982 as an affordable alternative to the DMX. It featured 18 drum sounds with 6-voice polyphony and used a similar voice architecture to the DMX except with the six voices contained on a single board and sound changes being possible via replaceable EPROMs. Like the DMX, users could tune and mix each drum voice. It could store 100 sequences and 50 songs in 8K of memory. The DX only had 6 faders and triggers on its front panel instead of the 8 of the DMX. Factory MIDI was later added on the DXa. The DX would later be able to interface with the Stretch for an addition 4 voices and MIDI functionality.



The last of the OB series, the Oberheim OB-8 was a powerful eight voice analog polyphonic synthesizer. The fully programmable OB-8 could store 120 patches, had a polyphonic arpeggiator, and was bi-timbral with various split and layer options. One of the unique characteristics of the OB-8 was its innovative Page 2 functionality: a microprocessor-driven feature that enabled users to access a completely new set of functions using the same set of front-panel controls. This design allowed for greatly expanded modulation capabilities. The Page 2 features were screened on the front panel in light blue on most OB-8 units (early units had Page 2 features, but not the screening). Equipped with Oberheim digital Interface bus, the OB-8 became the centerpiece of the last version of the Oberheim System when connected to the DMX and DSX. Introduced just before the adoption of the MIDI standard, later OB-8 models included MIDI functionality.



The Prommer was an EPROM chip burner designed for use with the DMX and DX series drum machines, but could also burn EPROM chips for other devices of the era. Users could sample their own sounds and add effects, like reversing samples, ring modulation, and basic envelope functionality. The end result was a custom 8-bit monophonic sample that could be triggered by the early digital drum machines of the day. The device was impressive for its time, adding a level of sample manipulation that is now widespread among DAWs.



While other companies in the mid-80s moved toward all-digital synths, Oberheim’s next instrument remained mainly analog, with the power of digital control. The Xpander was released in 1984, and still stands as one of the most flexible synthesizers of all time. This six-voice multi-timbral polysynth set out to recreate the patchability of earlier modular synths while retaining the lush analog sound Oberheim was known for. Each voice of the Xpander had two VCOs each with a dedicated level VCA and waveshape mixing, a 15-mode filter, two output VCAs, seven-position panning control, five LFOs, five envelope generators, a lag processor, four ramp generators, and three tracking generators. Individual presets could be stored in one of 100 locations (Single patches), and independently assigned to each voice with versatile split and layering capabilities into 100 addition locations (Multi patches). The first Oberheim synth designed for full MIDI integration, the Xpander provided more MIDI control than any other synth of its era, including velocity, release velocity, mono and poly aftertouch, with assignable MIDI channel per voice. In addition to MIDI the Xpander could be controlled via six dedicated CV and Gate inputs, making it directly compatible with modular synthesizers as well. In production until 1988, the Xpander sounded warm, lush, and complex, with highly intricate modulation possibilities.


Matrix 12

Released in 1985, the Matrix 12 put two Xpanders in an integrated unit along with a Oberheim’s first velocity (and release velocity) keyboard. The result was a 12-voice digitally controlled analog synth with a 61-note keyboard. Like the Xpander, the Matrix 12 had a whopping 47 modulation destinations and 27 modulation sources. Just like modular synths, users could create dense patches, but now for a polyphonic synth with a keyboard. The Matrix 12 was capable of lush, complex sounds and remains one of the most beloved synthesizers of the last 40 years.



Released in 1985, the Xk was a 61-key MIDI keyboard with velocity and aftertouch. It featured an arpeggiator, transport controls, switchable velocity curves, keyboard zone allocations, chord memory, release velocity and MIDI patch switching for up to 100 patches. Intended as the perfect companion for the Xpander as well as any other MIDI synthesizer module.


Matrix 6

The Matrix 6 was released in 1985, aiming to be a more affordable and smaller polyphonic synthesizer from Oberheim. Classic knob-per-function controls were replaced with a small membrane interface, though the Matrix 6 was still programmable and could store 100 patches plus 50 splits. It was a 6 voice bi-timbral synthesizer with a single low pass filter, 12 digitally-controlled oscillators, 12 VCAs, 3 envelope generators per voice, ramp generators and 2 LFOs. The Matrix 6 had a 61-note keyboard with velocity and aftertouch and full MIDI functionality.


Matrix 6R

With the growing use of synthesizer modules, the Matrix 6R was a logical extension to the Matrix lineup. It contained the identical voice architecture and user interface as the Matrix 6 but was housed in a 3U rack mount chassis.


Matrix 1000

Released in 1987 and in production until 1994, the Matrix 1000 was a preset-based rackmount synthesizer with 1000 presets based on the Matrix 6’s voice architecture. It was a 6 voice, multitimbral polyphonic synthesizer that was designed to have the Matrix sound yet fit easily within a rack setup at only one third the height of the Matrix 6R. Patches could be edited on a MIDI controller.


The Gibson Era

Tom's company, Oberheim Electronics, Inc., went bankrupt in 1985 and the company assets were acquired from the bank by a group of lawyers who changed the name to Oberheim ECC. Tom continued as an employee, although he left the company within a couple of years to start his new company, Marion Systems. In 1988, Gibson Guitar Corporation, acquired the Oberheim brand and for a few years continued to make several of the existing Oberheim products such as the Xpander and Matrix 1000. Several other products with the Oberheim brand were released during the Gibson era, although none of them involved Tom Oberheim. The OB-Mx was released in 1994, and after that most Oberheim-branded products were produced under license by Viscount International. Products included digital organs, pianos, and in the year 2000, a digital synthesizer called the OB-12.

By the late 2000s Gibson seemed to have stopped pursuing new products under the Oberheim brand. Tom Oberheim began making synthesizers under his own name again in 2009, and in 2019 Gibson formally returned the Oberheim trademark. 40 years after it all began, the "circle r" Oberheim trademark again belongs to the man who started it all, Tom Oberheim.


Marion Systems MSR-2

During the Gibson era, Tom produced some products under his new company name, Marion Systems. The Marion Systems MSR-2 was a new-concept modular synthesizer system utilizing a high-level mainframe/module implementation. The one-U rack mainframe could accommodate up to two eight-voice, eight-way multi-timbral analog synthesizer modules(ASMs). Other mainframe features included a six-input programmable mixer including external inputs, and a seven-band programmable stereo graphic equalizer. Superpatch storage allowed storage of all system parameters including the module data, as well as mixer and equalizer settings.

The Analog Synthesizer Module (ASM) was a complete eight-voice, eight-way multi-timbral analog synthesizer plug-in module utilizing custom integrated circuits developed by Marion Systems. In addition to the classic VCF, VCA sound, the module utilized unique high-resolution oscillators (HROs) that sounded analog but achieved digital stability. The HROs had six different waveforms available. Additional features of the ASM included: 2 pole/4 pole filter, noise generator, voltage controlled PAN, two LFOs plus vibrato, and three envelope generators and two ramp generators. Extensive modulation matrix was provided.


Marion Systems ProSynth

The ProSynth is a one-U rack analog music synthesizer that utilizes one Analog Synthesizer Module (ASM). All of the features and sounds of the ASM have been retained, but without the MSR-2 mainframe features. Just like the ASM that is included with the MSR-2, the ProSynth can play up to eight different timbres at once controlled independently over any of the 16 MIDI channels or layered four deep on a single key.


SeaSound SOLO

The SeaSound SOLO was a standalone, studio-quality computer-based hard disk recording/playback interface that communicated with either a PC or Mac computer through a custom PCI card. The SOLO features included:

Two custom microphone pre-amps with 48V phantom power
Two high-impedance instrument pre-amps
Two line inputs, inserts, direct outputs & auxiliary inputs
Built-in mixer with two headphone amps
24bit/96k A/D & D/A converters
Signal activity, clip indicators & 10 segment VU meters
S/PDIF In & Out, at standard sample rates

The device included mixing controls for mixing input signals with the audio already recorded in the host computer, as well as mixing together live sounds coming into microphones along with MIDI tracks coming from instruments all in stereo ready to record into the computer.

The SOLO was packaged as a two rack space unit came complete with a PCI bus controller card, cable, how-to video, CD-ROM with application software and instruction manual.


SEM Patch Panel

Tom reissued the synth that started it all, the Synthesizer Expander Module, in 2009, the first official synthesizer to carry Tom Oberheim's name in over a decade. The new SEM used nearly the same circuitry as the original, retaining the original sound and the internal modular patch-point capabilities. It used the same multimode VCF and voice architecture that fans knew and loved from 35 years prior. New to this generation of SEM was the addition of 33 connection points on a patch panel for interfacing with Eurorack modular synths.



In 2010 the new SEM was modernized further with the addition of a MIDI-to-CV section that made interfacing to MIDI gear and computers much easier. In addition to pitch control, other modulation sources could be routed from MIDI, and an audio input preamp circuit allowed for external audio signals to be processed through the SEM filter.



The next SEM combined the best of the Patch Panel and MIDI-to-CV versions and was called the SEM Pro. It included 21 patch points, an audio preamp, portamento, filter tracking, various assignment modes, LFO retriggering, transposition, and a MIDI to CV interface. The three different versions of SEM were all available from Tom Oberheim for several years, and are still highly sought after today.



Tom’s favorite synth from the original Oberheim era is the Two Voice. After the rerelease of the SEM, he brought back the TVS with a number of additional features that made it a truly unique and versatile synthesizer. Sonically, the SEMs were the same as their individual reissue. However, they could be controlled by a velocity sensitive Fatar keyboard with after touch and/or a new and improved sequencer module. This module came a long way from the original Mini Sequencer: the new sequencer was a two channel, 16 step unit that could store multiple sequences and chain them into longer songs. It also had eighth, sixteenth, and triplet ratchet modes, as well as sample/hold. There were a whopping 56 patch points on the top panel in addition to six 1/4" jacks on the rear, as well as MIDI in, out, and thru. The SEMs could be split across the keyboard, played in unison, duophonically, and have the sequencer control either one or both. Bend box controls added pitch and mod wheels, as well as a global vibrato LFO and VCO 2 detune. Another addition to the influential SEM line, the TVS Pro marked a full-circle point for Tom and his timeless instruments.


TVS Pro Black

A year after the TVS Pro was launched, a limited number of black-panel version were made. With only a little more than one hundred units made, these are the rarest of Oberheim Two Voice models ever produced. They are identical in every way to the TVS Pro with the exception of the panel color.


Sequential OB-6

Tom has always loved polyphonic synthesizers, so when Dave Smith of Sequential approached him about a collaboration it created the perfect opportunity for Oberheim polyphonic synthesizers to return. Sequential put six voices of classic analog Oberheim synthesizer circuitry based on the original SEM into a powerful and versatile platform that has reintroduced the Oberheim sound to countless new players. The OB-6 continues to be a powerful and popular analog synth that gets enthusiastic use from a wide range of current artists.


Sequential OB-6 Desktop

Later the same year as the introduction of the Sequential OB-6 was the launch of its companion Desktop version. With all of the same sonic power as its keyboard cousin, the Desktop version provides a compact and more affordable way to add the Oberheim sound to any existing MIDI or computer rig. It can also be combined with an OB-6 to expand the polyphony to 12 voices with its PolyChain feature.


TVS Pro Special Edition

Although the last TVS-Pro was manufactured in 2018, interest in this synth has continued. By popular demand, in May of 2021 Tom brought back the TVS-Pro as a Special Edition, with each unit now having the original "Oberheim" logo badge, plus Tom Oberheim's personal signature. Despite there being no formal announcement, hundreds of musicians inquired on this website as to how they could purchase one. The demand was much higher than the small number of units that Tom was able to build, so people were selected at random from the inquiries in order to buy one. In just one day all the built units were spoken for, which unfortunately left many people disappointed. Although we would like to make more units available, current parts and resource shortages do not make that possible at this time.