At the 1978 mini-NAMM show in the basement of a Disneyland hotel in Anaheim, California, Tom Oberheim saw something that would change the direction of his fledgeling synth company. That something was an early prototype of the Sequential Circuits Prophet-5—an instrument that would quickly change the face of the synthesizer business.

Tom was a computer engineer with an interest in sound. He'd been building ring modulators, phase shifters, and other effects since around 1969. In 1974, he developed the SEM (Synthesizer Expander Module), which came out of his experience as a West Coast dealer for ARP, who at the time were marketing their ARP 2600 synthesizer, Odyssey, and other instruments. With the SEM, Tom aimed to produce the simplest form of synthesizer he could. It would have a pair of oscillators, a filter, VCA, pair of envelopes and an LFO—which Tom considered to be the basic synthesizer building blocks.

×

The SEM was different from similar synthesizers at the time, like the Minimoog or ARP Odyssey, because it had a 2-pole filter rather than the more aggressive 4-pole filter that other synths were using. The filter was state-variable, designed by Dave Rossum of E-Mu, and was capable of low, high and bandpass modes without self-oscillation. It was a calm, smooth, and cuddly filter that gave the SEM a distinctively warm tone. Tom also developed a way to combine two and then four SEMs into a polyphonic instrument using another Dave Rossum innovation, the digital scanning keyboard. The Two-Voice and Four-Voice synthesizers were the first commercially available polyphonic synthesizers, and were followed a year later by the huge Eight-Voice synthesizer that simply doubled up on the Four-Voice panel.

So, when Tom came across the Prophet-5 at that first Anaheim-based NAMM show, it wasn't just the polyphony that interested him; it was the fact that all the voices responded to a single set of controls, the oscillators tuned themselves, and that you could save patches. The Two, Four, and Eight-Voice SEMs had to be programmed individually, giving it a unique character—but making it laborious to use compared to the instant, portable, and instrument-like nature of the Prophet-5. Once the Prophet-5 hit the market, Oberheim's sales quickly plummeted. Tom and his designer Jim Cooper realized that they would be out of business if they didn't do something.

It was this environment of pressure and uncertainty that gave birth to the Oberheim OB Series of synthesizers. They had to start from scratch, invest in microprocessor development systems, and work out how to inject a layer of digital control into an analog synthesizer sandwich. At the 1979 summer NAMM show in Atlanta, Oberheim revealed a barely working prototype of the OB-X, which was essentially based on the SEM with the addition of voltage-controlled envelope generators. They took around half a million dollars in orders that weekend and cemented Oberheim as a serious player in the synthesizer game.

Oberheim OB-1

Let's back up a bit, though—because there's a slight time rift in the story. Before Tom saw the Prophet-5 and took steps to invent the OB-X, Oberheim had already released the OB-1. The intention behind the OB-1 was to make a more accessible, programmable, and live-performance-friendly version of the SEM (and…to inadvertently get a prominent Star Wars character named after it?).

Oberheim had already invented a programmer unit for storing knob positions of the Two/Four/Eight Voice synthesizers, and so they didn't need Sequential to tell them how important and useful patch storage was. At this time, microprocessors were still too expensive, and Oberheim—recalling his prior career as a computer engineer—did not see early microprocessors as being serious computers. As such, Oberheim's company did not fully embrace microprocessor technology until the Prophet-5 more or less demanded it. So instead, for the OB-1 Tom and Jim designed a digital logic system to store the synth settings in 8 memory slots. It was simple stuff and mostly captured the envelopes, LFO, and modulation levels. It looked every bit like a stylish, exciting lead synthesizer and was revealed at the 1977 summer NAMM.

The OB-1 had two VCOs with variable waveforms from triangle to square. It had oscillator sync, cross-modulation, and sub-bass on both. The filter went beyond the 2-pole SEM to include the popular 4-pole design that other synths used, along with keyboard tracking. The envelopes were widened into fully ADSR stages, there was a single multi-wave LFO and a noise generator. Everything a cool little lead monosynth needed, and one of the first where you could change sounds at the touch of a button.

By the time it got to market in 1978, the Prophet-5 had announced the end of the era of monosynths and so the OB-1 didn't really have the life it deserved, and as with its cinematic namesake, left us too soon. With the release of the OB-X in 1979, Oberheim updated the OB-1 with similar colors and front panel design, but all eyes were on the new programmable and affordable polysynths.

Oberheim OB-X

So, when we last left the OB-X, it was holding itself together on a table at the 1979 NAMM show. It made a huge impression. It consolidated the sound of the SEM into an instrument with a single set of controls to cover all the voices and a microprocessor-driven patch memory. It slotted in perfectly as a sonic alternative to the Prophet-5, and with 4, 6, and 8-voice versions, it had a few more notes to knock around. In fact, the "X" in OB-X was originally supposed to stand for the number of voices, but OB-X seemed to stick.

The OB-1 is often seen as a monophonic version of the OB-X—when, actually, the opposite is true. The OB-X took on the same sort of architecture as the OB-1 with the expanded envelopes, cross-modulation, and LFO with multiple shapes, but it kept to the single 2-pole state variable filter. Instead of a logic system, Oberheim had to embrace the Z-80 microprocessor to provide the digital control over the voice cards, the automated tuning process and the 32-slot preset memory. The OB-X retained the polyphonic portamento and Sample & Hold from the previous polyphonic SEM synthesizers, which was quite unique.

Another unique feature was the response to the Prophet-5's pitch and modulation wheels. The OB-X used paddles, similar to those on the Yamaha CS-80, which were designed to mimic the motion of a guitarist bending strings. It works differently to traditional pitch wheels; with the paddles, you pull it towards you to pitch bend up and away to bend down. The paddles would remain a feature across the whole OB Series.

Oberheim OB-SX

The OB-X was big, heavy and expensive, and while it was a fantastic machine for the studio and sound design it was less great for live performance unless you had a road crew. And so, in a similar way to what Moog did with the Polymoog Keyboard, Oberheim released the cut-down and road-ready OB-SX in 1980.

The OB-SX removed nearly all the controls and left you a space that would be perfect for the OB-1, MiniKORG, or some other lead synth. You still had some knobs for a bit of envelope, filter and LFO control, but the idea was that in live performance, you just needed to play rather than tweak or explore tones. The internal architecture was based on the OB-X, but Oberheim moved to the Curtis ICs for the VCO and filter, and away from the discrete circuits of the SEM.

The first version came with 24 presets and shared the style and colouring of the OB-X. The presets were inspired by funk and progressive rock music of the time and could be upgraded with another bank of 24 sounds. A later version included 56 presets and took on the blue pinstripe look of the OB-Xa, which arrived in 1981. Apparently, you could send in a tape dump of sounds taken from an OB-X, and Oberheim would put these into the OB-SX for you so that you could take your own sounds on the road.

Oberheim OB-Xa

The OB-Xa represented the evolution of the OB-X into a mainstream and ultimately legendary synthesizer that could take on the might of the Prophet-5. It fully embraced the Curtis integrated circuits that Oberheim had explored in the OB-SX, which increased reliability and stability—and made it cheaper to buy and easier to service. Fortunately, the overhaul of the electronics didn't have much of an impact on the overall tone, but there were plenty of improvements that made a big difference in how it worked.

The two-filter approach of the OB-1 finally made it onto the bigger synth, which satisfied those who wanted a more Moogy sound. The cross-modulation was now being fed by the filter envelope, which did very interesting things to the sync sound. There were now three LFOs, unison mode, a chord memory, and sample & hold. The eight voices could be split into two four-voice synthesizers for bi-timbral splits or layers and could be independently controlled via the modulation paddles. This was very innovative at the time.

With the OB-X, you had to hit a button to enter Edit mode to create and store a patch. On the OB-Xa, the controls were always active; they would add or remove from the stored values rather than jump like other synths, and they could be overwritten at the touch of a button. Originally, it had room for 32 programs, but was raised to 120 over time.

Oberheim wasn't really involved in the development of MIDI, which was just around the corner, so they had come up with their own system of connectivity. The Oberheim System was a 37-pin computer interface that allowed you to connect two OB-Xa's together or hook up to the DMX drum machine or DSX sequencer that were released at the same time. It really showed how mature and innovative Oberheim had become.

Oberheim OB-8

The innovation in the 1983 OB-8 was in the software. Some say the extra layer of control, the reliability, and the fully mature Oberheim System connectivity made the OB-8 the pinnacle of analogue synthesizer design, whereas others will say that it just didn't sound quite as fat as the OB-Xa. Maybe it's because the tuning was slightly better, which is always a pro and a con, depending on your point of view.

What's clear is that the OB-8 was a next-level eight-voice synthesizer. You now had seven LFO waveforms, versatile modulation routing, voice panning, an additional VCO triangle waveform with waveform mixing, a bi-timbral arpeggiator, and a whole host of new ideas in the "Page 2" concept. With a double tap of a button, many of the controls have entirely new functions. You could turn voices on and off, detune the oscillators, quantise modulation, add envelopes to LFO depth and frequency, interact with portamento, and more. If you just wanted to play a synth, you didn't have to worry about the additional depth, but if you wanted to get into the guts of designing sounds, then the second page of the OB-8 was amazing.

MIDI made its way onto the OB-8, first as an upgrade and then fully integrated into later models, which helped it play nice with instruments outside of its own ecosystem.

Inbetween

With the arrival of the Yamaha DX7 in 1983, things changed in the synthesizer industry. But Oberheim moved with it and shifted to the Matrix range of analogue synthesizers, finally brought in velocity-sensitive keyboards and continued to innovate.

Bankruptcy came in 1985 through some bad accountancy and legal advice rather than a lack of sales. Tom Oberheim left the floundering lawyer-led company in 1987, and it was sold to Gibson in 1988. In the 1990s, Gibson-led Oberheim released a number of curious products which attempted to cash in on the Oberheim + OB Series legacy.

The OB-Mx

Gibson attempted to revive the Oberheim name with the 1994 OB-Mx. The OB-Mx has a storied development history—going through several major hardware revision with generally poor project management. Toward the end of the project, they brought in Don Buchla to head up the design team, along with his long-time collaborator, programmer D.N. Lynx Crowe. This is one of the last self-contained synthesizers that Don Buchla worked on, but it was not a true Buchla invention—he just helped to get it across the finish line after the ball had been dropped by prior product managers. The idea was to pull the analog Oberheim sound into a modern machine.

The signal path is all analog with digital control over the 12 voices, and it's all built into an alarmingly big rack-mounted box. On the front panel, you have a 40-character, 2-line display and 32 knobs controlling the two VCOs, VCFs, VCA, four envelopes and three LFOs per voice.

It was released to decidedly mixed reviews, and never gained great success as a product. Some say the filters are not really up to scratch and don't sound like the SEM and Ladder designs they are supposed to mirror, whereas others believe it was the best analog synth to come out of the 1990s. It was certainly expensive compared to the digital workstations that surrounded it.

The OB-12

The Oberheim OB-12 has the name, but none of the original team that gave us the classic Oberheim sound. The OB-12 was designed and built by the Italian company Viscount. It was released in 2000 as a 12-voice, DSP-based virtual analog synthesizer competing with the likes of the Roland JP-8000, Yamaha AN1X, and Korg MS-2000.

It has a huge screen, a vast array of controls, its 4-part multitimbral, has an arpeggiator, phrase recorder, program morphing and automation recording. It was impressive, well priced and remains a popular keyboard of its time.

While it is an interesting footnote in synthesizer history, it's not exactly what we would call "an Oberheim."

The Return

In the early 2010s, Tom dabbled with the idea of returning to synthesizers. The SEM was reissued under his full name of "Tom Oberheim," as he didn't own the Oberheim brand name. In 2011, the SEM Pro came with patch points, and I even remember seeing a Eurorack version at the NAMM show around that time, but it never materialized as a product.

In 2015, he was able to do a short run of the original Two-Voice as the TVS Pro. But then Tom and Dave Smith, founder of Sequential and Dave Smith Instruments, had a conversation.

Sequential OB-6

Tom was impressed by the Prophet-6, released in 2015, around the time that Dave Smith got the name Sequential back from Yamaha. It was the long-awaited homage to the original Prophet-5, but with a thoroughly modern hardware and software architecture. They'd talked about coming up with a new version of a classic OB synth, and the Prophet-6 had all the technology and facilities that could make that a relatively straightforward reality. All they needed was a voice card that was fully SEM rather than fully Prophet.

So, between them, Tom and Dave came up with a compatible voice card version of the classic SEM synthesizer and a design for the front panel, and you have a new synth in a similar form but completely tonally distinct. The voice cards go as far as to use discrete components rather than ICs to produce the two VCOs, the VCF and a smattering of VCAs needed for the programmability.

Oberheim OB-X8

Which brings us finally to the ultimate return of the Oberheim synthesizer; the OB-X8. In 2021 Music Tribe, in a gesture of goodwill, gave Tom his old name and brand back. To celebrate he produced a handful of special edition TVS Pro synthesizers, but behind the scenes, Sequential had been bought by audio brand Focusrite, and Tom thought there would be great synergy in Focusrite taking on the Oberheim brand as well. Tom was trying hard to be seriously retired, but he took a great interest in what Focusrite and the Sequential engineers would do with it.

The OB-X8 was designed to pull in all the best aspects of every OB synth into one glorious instrument. The looks reflect the original OB-X rather than the later OB-Xa or OB-8, and is very familiar, although less deep and heavy. The knobs are luxuriously wide apart, like they've got all the space in the world, which feels slightly strange compared to the dense controls on most modern synths.

The character of each OB series synthesizer can be recreated on the OB-X8, and in the combination you end up with something that is amazingly greater than the sum of its parts

Future OB?

Does there need to be another one? Since the OB-X8 Focusrite has released the Oberheim TEO-5, which explores new avenues of modulation to take the Oberheim tone into unexpected places. Maybe we've seen all we need to of the classic OB architecture, though—it's difficult to imagine how one could develop on the true masterpiece which is the OB-X8.

No matter what, it will be interesting to see what Oberheim cooks up next.

Be sure to check out our interview with Tom Oberheim here!