At Winter NAMM 2009 a keyboard player of note approached us with a list of desirable vintage equipment asking if we were interested in making a purchase. Frankly, if we’d had the funds we’d probably have bought everything, but two instruments stood out so we decided to throw financial caution to the wind and, if necessary, sell a couple of vital organs in order to become their custodians.

One of these instruments was an Oberheim 8-Voice and with a deal struck we returned to the UK and excitedly awaited its delivery.

While we’d been informed there was no provenance by way of certificates or pictures, our 8-Voice had been previously owned by Chick Corea and when it finally arrived on the 8th March 2009 we were thrilled to see the custom flight-case emblazoned with ‘Chick Corea World Tour 1978’ plus an address of Griffith Park Blvd, Los Angeles. This is currently listed as Mad Hatter Studios and was originally established by Mr Corea back in the 1970s. Opening this custom flight-case revealed an instrument of our dreams and it’s fair to say that day marked the start of an enduring love affair with the 8-Voice.

While the instrument is a physical monster, the concept of the 8-Voice is actually very simple; based around a single Synthesiser Expander Module (SEM) containing two VCOs with Pulse and Sawtooth waveforms, two ADS Envelope Generators, one LFO and a magical Multi-Mode Filter. In isolation a SEM is monophonic, but in the 8-Voice, because there are eight SEMs triggered by a polyphonic keyboard we have the potential for eight note polyphony.

The Oberheim SEM was first produced in 1974 by Tom Oberheim, a physics graduate of UCLA who, via a series of fortunate events, was inspired by a Harald Bode electronics article to build a ring-modulator for the band The United States Of America, and jazz trumpeter Don Ellis in the mid-1960s. Over time other notable musicians and film composers recognised the musicality of Tom’s work with electronics and in 1969 he was approached by the product manager of Chicago Musical Instruments Company (CMI) asking if they could market Tom’s products. Tom’s first product was the Maestro RM-1A Ring Modulator, and following its success Tom followed up with the Maestro PS-1 Phase Shifter, having been inspired by musicians who were playing guitars through Leslie Cabinets. Approximately 75,000 PS-1’s were built by Tom - pretty incredible from a small operation run out of Tom’s spare bedroom.

Following an early 70s NAMM show, where he first encountered an ARP Synthesiser, Tom became an ARP dealer and sold 2600’s to various movie composers and local musicians and subsequently designed a modification that enabled the 2600 to be played duophonically. In 1973 he also released the second ever commercial digital sequencer (the first being the EMS), the DS-2 resplendent with three tracks and a total of 144 notes.

This was a fertile time for Tom who decided to build a small module that was designed to compliment and expand the tonal palate of existing synthesisers, including ARP’s and Moog’s, resulting in the birth of the SEM. At the time most synthesisers featured 24db per octave Low-Pass filters whereas the SEM contains a 12 db per octave Multi-Mode filter featuring Low-Pass, High-Pass, Notch and Band-Pass filter modes.

Tom recalls. “Those were in the days when the typical musician would have only one synthesiser that you could play by yourself, or my digital sequencer could play it, but you couldn’t do both. So, I came up with this idea to develop what I thought would be the absolute minimum, but still fully useful, synthesiser module. That became the SEM. Then you could have the digital sequencer play the SEM, while you played your synthesiser.”

In January 1975 CMI (which had now become Norlin) cancelled all orders for Tom’s effects pedals forcing him to take drastic action to save his business. After chaining four of his expander modules together and attaching a digitally scanned polyphonic keyboard, licensed from E-mu, in June 1975 he showed prototype versions of the SEM based 2-Voice and 4-Voice instruments at the Chicago NAMM Show. According to Tom this was the first time a true polyphonic synthesiser had been shown at a trade show and afterwards, via a mutual friend, Tom was introduced to Stevie Wonder who, after a short demo, bought the 4-voice prototype.

“Actually the 4-Voice that Stevie ended up with was a very rough prototype, including all wire-wrap wiring internally. In the fall of 1975 a friend who knew Stevie asked me if I would like to meet him at a studio in Hollywood where he was recording a new album. I said “sure” and my friend said “bring along the 4-voice prototype”. We went to the studio, walked in with the 4-Voice, my friend introduced me, Stevie played on the instrument for a minute or two and said: “Can I buy it?”. That’s the last time I ever saw it.” recounts Tom.

While true four note polyphony was a serious achievement back in 1975 to achieve eight note polyphony a supplementary case containing a further four SEMs was made. After hooking this case up to a 4-voice via a couple of umbilical cables, the user was able to play eight note chords via the single polyphonic scanning keyboard.

This was manna from heaven for keyboard players, but all this power didn’t come without responsibility. For each note played on the keyboard, SEMs would trigger sequentially - the first note of a chord would play SEM 1, the second SEM 2, the third SEM 3 etc. So if you wanted to play a uniform sound, polyphonically, across every note, each SEM had to be set up identically. Given that we’re talking analogue electronics with all the tuning issues and subtle vagaries that go with that technology, this represented a real challenge. Furthermore, if you wanted to change the sound to yet another uniform polyphonic sound, it would entail changing all eight SEMs to an identical setting. That’s a potential of 160+ knobs - not ideal in a live situation.

Remember, this was before the micro processor controlled memories that would later become available on instruments such as the Prophet 5. While Tom later released a programmer section that helped in situations like this, in practice it was a bit of a fudge and really only good for storing global settings of the 4 or 8-voice. Nonetheless, the sound of a SEM, and especially those within a 4 or 8-Voice is something to behold so musicians were soon queuing up to become part of the Oberheim club.

One such member was Joe Zawinul who called Tom in 1976 to say said he’d bought an 8-Voice and would really appreciate some advice on how to use it. Tom visited him and tried to explain the various intricacies of the instrument but left thinking that his explanations had been largely misunderstood. However, several weeks later Joe called back and invited him to his studio where he played him the seminal SEM based track, Birdland.

According to Tom, the 4-Voice and 8-Voice were initially adopted by artists with a jazz focus, musicians including Herbie Hancock, Joe Zawinul and of course the aforementioned, Chick Corea. Those with rock influences followed rapidly, artists including; Rush, Styx, Supertramp & Patrick Moraz. Eventually a small army of users had to have that ‘Oberheim’ sound including Earth Wind & Fire’s Larry Dunn, George Duke, Rose Royce, Jam & Lewis, Prince, Frank Zappa, Michael MacDonald, Jan Hammer, Lyle Mays and many more.

So what is the fabled Oberheim sound? It’s a tricky one to answer because the Oberheim lineage is wide and varied, from the 2, 4 & 8-Voice SEM based instruments, to the OBX, OBX-a, OB-8 and Matrix 6 & 12 range. Each have their own sonic character, but the adjective that’s probably most used when describing 90% of Oberheim instruments is ‘creamy’.

SEMs are not used for effects or massively punchy bass lines - those are best taken care of by other instruments - but the SEM’s 12db per octave Multi-Mode filter, (with continuous control from Low-Pass to Notch and High-Pass, plus a switchable Band-Pass mode) is very musical sounding, and its lack of aggressive resonance and self-oscillation definitely contributes to the instrument’s ‘creamy’ description. Some might say the filter is the SEM’s crowning glory.