VCO: Discrete or chip-based, which is better? Does it matter? When I bought my Sequential Prophet-6 it was touted as great because it had VCO’s constructed from discrete components (like the original Prophet-5 synthesizer keyboards). Oberheim’s first synthesizer, the Synthesizer Expander Module (SEM) also was famously made from discrete components. Oberheim managed to take the original discrete SEM and make it into a polyphonic synthesizer, albeit a very expensive instrument (original four and eight voice synthesizers used multiple SEM modules).
In a parallel universe Dave Smith was innovating with the original Sequential Prophet-5 (five voice). Both of these great synth designers started by using discrete component designs and both migrated to using chips by Doug Curtis, creator of the famed 3340 VCO, on a chip, known simply as CEM. These chip based synths were the ones that were most popular by sales volume, playability and tuning-stability. The debate continues on today about which of these build schemes produces better sound. I think the most important thing is the music you make with any of these instruments but I still find their stories to be almost as fascinating as the instruments themselves.
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| Tom Oberheim (L) and Dave Smith (R) with OB-6 by Sequential |
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| Mr. Oberheim with 2-voice SEM (love the screen door handle) |
SEM: Synthesizer Expander Module
In 1969, Tom Oberheim, a trained physicist with a passion for jazz and electronics, founded Oberheim Electronics in Los Angeles. Initially, the company focused on building effects units for Chicago Musical Instruments under the Maestro brand, such as the RM-1A Ring Modulator and PS-1 Phase Shifter. However, Oberheim’s fascination with synthesizers led him to develop the Synthesizer Expander Module (SEM) in 1974, a compact monophonic synth designed to complement instruments like the Minimoog or ARP 2600.
The SEM was a revelation in its simplicity and power. With two voltage-controlled oscillators (VCOs) offering sawtooth and pulse waveforms, a multimode filter (low-pass, high-pass, band-pass, and notch), and two envelope generators, it delivered a fat, warm sound that became a hallmark of Oberheim’s designs. The SEM’s modular nature allowed it to be integrated into larger systems, such as the Two Voice, Four Voice, and Eight Voice synthesizers, which combined multiple SEMs in flightcase-style enclosures. These were among the first multitimbral synthesizers, allowing each module to be assigned to different keyboard ranges, a groundbreaking feature for polyphonic music.
The SEM’s discrete circuitry and hands-on design resonated with musicians like Herbie Hancock and Jan Hammer, who appreciated its raw, expressive sound. It laid the foundation for Oberheim’s reputation as a purveyor of lush, characterful analog tones, setting the stage for the company’s ambitious leap into fully programmable polyphonic synthesizers.
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| The OB-X |
The OB-X: Polyphony Meets Programmability
By the late 1970s, the synthesizer market was heating up, with Sequential Circuits’ Prophet-5 (introduced in 1978) setting a new standard for polyphonic, programmable synths. Oberheim responded in 1979 with the OB-X, the company’s first fully integrated polyphonic synthesizer, available in four-, six-, and eight-voice configurations. Built on SEM circuitry, the OB-X used a single printed circuit board per voice, streamlining production while retaining the rich analog sound of its predecessor.
The OB-X featured two VCOs per voice, a 2-pole low-pass filter with its own ADSR envelope, a VCA with an ADSR, and a flexible LFO section. Its 32 programmable presets, automated tuning process, and polyphonic portamento made it a performer’s dream, while its Polymod section allowed for cross-modulation and oscillator sync, adding a layer of sonic versatility absent in later OB models. The OB-X’s paddle levers for pitch and modulation, inspired by guitar string bending, offered a unique performance interface, though they were less popular than the Prophet-5’s wheels (first introduced on the Minimoog in 1970).
The OB-X found favor with artists like Rush, Queen, and Prince, who used its bold brass and string sounds to define albums like Moving Pictures (1980) and The Game (1980). Despite its success, the OB-X was expensive—starting at $4,595 for the four-voice model—and faced stiff competition. Oberheim needed to innovate further to stay ahead.
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Each voice card in the OB-Xa contained two CEM3340 VCOs |
The OB-Xa: Streamlining for the Masses
In 1980-81, Oberheim released the OB-Xa, a successor to the OB-X that marked a significant shift in design. The OB-Xa replaced the discrete SEM-based circuitry with Curtis Electromusic Specialties (CEM) integrated circuits, specifically the CEM3340 VCO, CEM3320 filter and CEM3310 envelope generators. This change reduced manufacturing costs and improved reliability, though some purists argued it slightly tamed the OB-X’s raw edge. The OB-Xa also introduced Oberheim’s iconic blue pinstripe aesthetic, which became a visual hallmark of the brand.
The OB-Xa retained the OB-X’s polyphonic architecture (available in four-, six-, and eight-voice versions) but added bitimbral capabilities, allowing split and layered sounds. It also featured the Oberheim Serial Buss, a pre-MIDI protocol for interfacing with other Oberheim products like the DMX drum machine and DSX sequencer, marketed together as “The System.” This integration made the OB-Xa a staple in 1980s new wave, synth-pop, and hip-hop, powering tracks like Van Halen’s “Jump,” New Order’s “Blue Monday,” and Prince’s “1999.”
The OB-Xa’s success solidified Oberheim Electronics’ place in the industry, but the company faced challenges. The synthesizer market was becoming crowded, with Japanese manufacturers like Roland and Korg diversifying into effects and digital instruments. Oberheim, committed to analog, needed a bold new direction to maintain its edge.
The OB-8 was released in 1983 and it introduced several enhancements to the OB-Xa. The OB-8 had a Z-80 microprocessor and MIDI, two important things the Xa did not. The OB-8 used Curtis CEM3340 VCOs and CEM3320 filters which delivered a polished sound. The OB-8 introduced continuously variable filter slope (from 2-pole to 4-pole) providing greater sound shaping. Improved ergonomics, clearer front panel, dedicated knobs and more robust build, plus stereo output option and “Page 2” for deeper editing. Above other features the OB-8 featured improved tuning stability and reliability thanks to the microprocessor and refined circuitry.
The Xpander and Matrix 12: The Pinnacle of Modulation
In 1984, Oberheim unveiled the Xpander, a six-voice, keyboardless synthesizer that redefined analog synthesis. Designed by Marcus Ryle and Michel Doidic with input from Doug Curtis, the Xpander paired analog audio generation (VCOs, VCFs, and VCAs) with digital control, introducing the revolutionary Matrix Modulation system. This system allowed users to route any of 27 modulation sources to 47 destinations, offering near-modular flexibility without patch cables. Each voice boasted two VCOs, a 15-mode filter, two VCAs, five LFOs, five DADSR envelopes, a lag processor, four ramp generators, and three tracking generators, making the Xpander a sound design powerhouse.
The Xpander’s six-part multitimbrality allowed it to function as six independent monophonic synths, enabling complex arrangements within a single unit. Its MIDI integration, including velocity, release velocity, and polyphonic aftertouch, was unmatched for its time, and its CV/Gate inputs ensured compatibility with modular systems. Artists like Vince Clarke, Depeche Mode, and Hans Zimmer embraced the Xpander for its lush, intricate sounds, heard in tracks like Erasure’s “Stop” and Nitzer Ebb’s Belief.
In 1985, Oberheim released the Matrix 12, essentially two Xpanders combined with a 61-note velocity-sensitive keyboard. With 12 voices and the same Matrix Modulation system, it offered unparalleled polyphonic sound design capabilities. Jazz musicians like Lyle Mays and Michael Brecker used its complexity to craft evolving, expressive patches, while its warm, analog tone made it a favorite for lush pads and intricate sequences. However, the Matrix 12’s complexity and high cost limited its market to dedicated professionals.
The Fall of Oberheim Electronics
Despite the brilliance of the Xpander and Matrix 12, Oberheim Electronics faced financial difficulties. The company’s commitment to analog synthesis, while artistically lauded, struggled against the rise of digital synthesizers like the Yamaha DX7 and Casio CZ series, which offered affordability and new sounds. Oberheim’s first bankruptcy in 1985 led to its assets being acquired by a group of lawyers who renamed it Oberheim ECC. Tom Oberheim stayed on briefly as an employee but left in 1987 to found Marion Systems, frustrated by his lack of control.
Gibson Guitar Corporation acquired Oberheim in 1988 after a second bankruptcy, continuing production of the Xpander and Matrix 1000 (a preset-heavy, cost-reduced version of the Matrix 6) under Keith McMillen’s direction. However, Gibson’s focus shifted away from synthesizers, and by the early 1990s, Oberheim-branded products like the OB-Mx and digital organs (produced under license by Viscount International) bore little resemblance to Tom Oberheim’s vision. By 1988, Oberheim Electronics as Tom had envisioned it was effectively defunct, its legacy preserved in the enduring influence of its instruments.
Legacy and Impact
The journey from the SEM to the Matrix 12 reflects Tom Oberheim’s relentless pursuit of sonic innovation. The SEM introduced a modular, multitimbral approach; the OB-X brought programmability and polyphony; the OB-Xa streamlined production for broader appeal; and the Xpander and Matrix 12 pushed the boundaries of modulation and sound design. These instruments defined genres, from synth-pop to film scores, and their warm, analog tones remain sought-after today.
Oberheim Electronics’ downfall was a casualty of a shifting market, but Tom Oberheim’s contributions endure. In 2009, he began developing new instruments under his own name, and in 2021, he regained the Oberheim trademark from Gibson, partnering with Sequential to release the OB-X8 in 2022, a modern synth combining the OB-X, OB-Xa, and OB-8 architectures. The 2024 release of the TEO-5 further demonstrates Oberheim’s ongoing relevance.
For musicians and producers, Oberheim’s synthesizers remain a testament to the power of analog sound and innovative design. Whether it’s the raw punch of the OB-Xa in Van Halen’s “Jump” or the intricate layers of the Xpander in Erasure’s “Stop,” these instruments continue to inspire, proving that Tom Oberheim’s vision was not just of its time but timeless.
Thanks for reading High on Technology, Good Music To You!
©July 2025 by Mark King, It is NOT ok to copy or quote without written permission from the author.
Now, please go and create something beautiful, preferably analog ;-)
