Oberheim OBX, OBXa & OB8

The Oberheim OBX. Picture courtesy of the EMIS Synthesizer Museum.

Simon Lowther introduces the clan of classic American analogue synths.

Tom Oberheim entered the synthesizer business with his SEM and 4‑Voice models in the mid 1970s, and achieved considerable success. Oberheim synths quickly became known for a fat warm sound, raunchy brass and full strings, not to mention great bell and Hammond sounds. In 1978, however, their place at the cutting edge was threatened by the arrival of the milestone Prophet 5, the first of the microprocessor‑programmable and homogeneous‑sounding polyphonic synths we take for granted today. The OBX, unveiled in July the following year, was Oberheim's response.

OBX

The OBX had similar audio paths to the earlier SEM; on the OBX, however, they came under microprocessor control for full programmability. There were 32 programs storable in four banks of eight, named A, B, C and D. Continuing a tradition which had begun with the SEM, you could choose a four, six, or eight‑voice instrument and buy additional voice cards later, bank manager or album advances permitting. It was also quite easy to open up the OBX's hood to get inside, either to make quick repairs, defeat a wobbly voice, or get at the memory‑protect switch. If you ever do see an OBX opened up, you'll notice that there is an awful lot in there, which makes them big, heavy, and unfortunately of questionable reliability. The whole voice chain uses analogue components, with Curtis chips employed only for the envelopes. Perhaps as a consequence of this, every individual OBX can sound slightly different.

Though the trademark blue stripes appeared only on the later OB‑series synths, the original OBX's panel layout (shown here) was retained.

Voice Architecture: Oberheim's View

Although the OB series evolved over the years, and substantial improvements were made to the control system, the layout of the front panel remained remarkably consistent, and most of the OBX's panel features survived into the OBXa and OB8.

First of all, you got two VCOs delivering sawtooth or variable pulse waveforms. These were supplemented on the OBX by cross modulation and sync switches. Then came the mixer — not the OBX's most exciting feature, consisting as it did of just four switches. You could turn OSC 1, OSC 2 and white noise on or off, or use OSC 2 at half volume. Although this mixer attracted a fair amount of criticism over the years, Oberheim decided not to change it (for whatever reason) and kept the design for the subsequent OBXa and OB8.

The filter on the OBX was a resonant 12dB/octave lowpass, with cut‑off controllable from the dedicated filter ADSR. LFO modulation was also possible, and the filter's keyboard tracking was either on 100 percent or off. Although the VCF on the OBX was apparently related to the filter on the SEM, it lacked the latter's multimode settings, which I always thought was a bit of a shame. No doubt cost came into it, especially as the OBX was not cheap. The VCA had its own dedicated ADSR, and the single LFO offers triangle, square, and sample and hold waveforms for the usual duties, which included a big, swirly and effective PWM.

Performance Time

Each new model in the series added new features to the performance panel (this is the OB8's), but retained the OBX's innovative paddle controllers.

A major innovation on the OBX were the performance controllers, which took the form of two sprung paddles to the left of the keyboard. Though there was some doubt about these paddles at first, as Moog style pitch and mod wheels were very much the accepted standard, they proved to give such a balanced resistance, making control expressive and intuitive, that most players just loved them. There was also polyphonic portamento, which excited magazine reviewers at the time, unison for monster mono lines, and a nifty chord memory for huge one‑finger stab sounds. The later effect is great, especially for dance music.

On the back panel were sockets for vibrato, filter, hold and program advance. Interestingly, the OB series was stereo from the outset, with Left, Right and Mono outputs, but Oberheim never got round to putting a headphone socket on.

Though the OBX may seem pretty light on features by today's standards, it still possesses one overwhelming plus point — it sounds huge.

OBXa

It's generally true that a new product has to have some strong features to succeed against an established market leader, and Oberheim clearly knew that the OBX was not enough to take the crown from the Prophet 5. Early in 1981, therefore, the OBXa was introduced. Its appearance, like its name, did not suggest radical alterations — but Oberheim's improvements made all the difference. For one thing, it looked smarter, sporting the now‑famous black body with blue strips. For another, you could now split or layer two sounds on the keyboard, and 8 of each were storable, which was big news at that time on this sort of synth. It was, if not a first, a pretty close thing.

Beyond that, the synth engine had also been upgraded. The filter now had selectable 12dB or 24dB (2‑ or 4‑pole) rolloff, giving a nice choice of tone colours (apparently JL Cooper had already been doing this as a third party modification for OBX owners who wanted a 4‑pole Moog type sound). The cross‑modulation switch on the OBX was reassigned, and now connected the filter envelope to sweep the pitch of Oscillator 2, for those screaming sync sounds. Though the loss of cross‑modulation was a shame, I think this made up for it.

Inside, there had been a major overhaul, with Curtis chips employed throughout (buyers still got to choose a six‑ or eight‑voice instrument). Such a radical change of components meant that there was inevitably a change of tone, but it was a subtler one than might have been expected, and the OBXa had a wonderfully fat, powerful sound. An unequivocally positive consequence of the component change was that it made the OBXa lighter and a bit more reliable than its predecessor (though only a bit, as the availability of an optional road repair kit might suggest).

Extra Performance

The OBXa also benefited from significant improvements to the performance panel. The paddles could now modulate each VCO and split or layered part independently. There were also now three LFOs, one on the performance panel, and a programmable one for each of the two voice boards. Though there was only one set of controls on the main panel, each half of a split or layer could have its own modulation settings.

The OBXa's designers had also come up with some clever ideas to get more out of the available hardware. If you pulled the performance panel LFO knobs, they clicked upwards, whereupon the LFO depth knob now set the LFO depth directly, bypassing the paddle for continuous two‑LFO sounds. Raising the speed knob changed the waveform to sawtooth, and transpose and pitch bend were implemented on the second VCO. This was surprisingly effective, whether you used it when the VCOs were sync'ed or for expressively bending VCOs against each other. All of these were nice touches typical of a maturing system.

Oberheim OBXa keyboard synthesizer.Photo: Richard Ecclestone

Editing Time

On the original OBX, you had to enter edit mode by pressing a special button. The OBXa's controls, on the other hand, were always active. If you liked your edit, you could just write it in. Edits were very smooth, since moving a knob added or subtracted from the value stored in memory rather than jumping to the physical setting of the knob like a Jupiter or Prophet. If you wanted to clear the value and show the true setting, you turned the control fully left then right. For hard core programmers, there was a manual switch which disconnected the programmer so you could start from scratch.

The OBXa's auto‑tune feature is worth mentioning. Not only is it faster than that of the Prophet, but it is also more user‑friendly. When the tune button is pressed, the synth strolls through the voices displayed by the programmer LEDs so you can see its progress. Failed voices continue to flash when the auto-tuning is over, and if any are getting wobbly the tuner spends more time working on them, hovering on that voice while passing through. I much prefer this system to that of Memorymoogs and Prophets, which just shut down while tuning and can take quite a few seconds, leaving you to wonder if it will work out OK or not.

On the back panel, a 37‑pin computer interface appeared, designed specifically to link the OBXa to another OBXa/OB8 or to other Oberheim products like the DMX drum machine and DSX sequencer in what was termed the Oberheim System. While this was cutting edge technology at the time (remember, we are talking well over a year before the introduction of MIDI), it's unlikely to get used much today. Various updates increased patch memory from 32 to 120 programs, and improved the general running of the autotune and cassette interface. The extra sounds were selected by holding down multiple bank switches and then choosing 1 to 8. While the extra capacity was useful, patch names could get long winded (ACD5, for example), and sometimes you just couldn't remember where you'd put that sound!

With the OBXa, Oberheim were back on the map, and customers flocked in.

OB8

There is something of a difference of opinion about the OB8 amongst OBie afficionados. It was, undoubtedly, much more sophisticated, and the operating system gave it more features than the OBX/Xa and a more modern feel. Some say it was the best of the series, being a lot lighter (it had the same box as the OBXa, but with less in it), more flexible, and more stable (one of Oberheim's goals in increasing the degree of software control). The fall in component prices that had occurred throughout the '80s meant that the OB8 was cheaper to make than its predecessors, and so was bound to sell well.

There is, however, a body of opinion which says that the OB8 lacks power in the sound department compared to the OBXa and its forefathers, and it is possible that some of the very clever software calibration routines that give reliability do also contribute to a less vibrant sound.

The OB8 offered even more features, and greater reliability, than the earlier OBX and OBXa; some, however, would argue that it lacked their sonic punch.

The Sound

Before we consider the features which were new to the OB8, let's look at the argument about sounds. For annihilating heavy metal guitarists in a live mix, the OBXa or OBX is the one. Think Van Halen. The OBXa does seem to have shorter attack times than the OB8 and a fuller, gutsier sound. However, I have found that the OB8 can sit better in a mix when working with more recent synths, though I don't really know why. I've always found the OB8 strings smoother, and the extra modulation options lend themselves to a more polished and interesting sound. Tom Oberheim himself allegedly had some retrospective misgivings about the OB8 sound, claiming that the OBXa sound is fatter because its tuning is less perfect. The only answer, really, is to play both of them and see what you think. There is a difference and, though both are great, each has its own strengths and weaknesses.

In appearance, the OB8 is remarkably similar to the OBXa. There are more features to list on the front panel, and an end cheek is cutaway to reveal pan knobs for each of the eight voices. Apart from the early units, OB8s were factory fitted with MIDI. Mine has sockets on the other end cheek, while on later units MIDI moved to the back panel.

The idea of adding voice cards had been dropped, and the OB8 was, as the name suggests, an eight‑voice synth. In terms of programmability, it was considerably more versatile than the OBXa, offering seven LFO waveforms which could also be routed to the VCA for tremolo. Its VCOs could mix sawtooth and pulse waveforms for a fatter sound, and you also got a triangle wave. It's also worth noting that the OB8's memory‑protect switch was externally mounted on the rear of the unit.

Once again the performance panel had been upgraded, giving its LFO more waveforms (including white noise), and a rather fab Arpeggiator. Externally clockable, though unfortunately not by MIDI, it could control either or both parts of a split or layer, and memorise up to five preset transpositions as well as note order. This was way beyond usual Arpeggiator expectations, though sadly it only remembered its current setting.

A Second Page

Another feature of the OB8, which was very remarkable at the time, was that pressing the chord button twice in quick succession assigned most of the controls completely new functions — a halfway house towards parameter access. It was clear when the jump had been made because all the LEDS immediately switched to show new settings. The eight programmer LED's also came on, showing that voices were active. You could turn voices on or off with these, which was very comforting for live performers. If you're buying an OB8, it's worth checking here to see if any dodgy voices have been deactivated. On earlier OB8s none of these Page Two features were labelled, while on some later units they were detailed in faint blue writing, though I'm not sure how common these were. Apparently you could pay, in the States at least, to have the writing put on as a retrofit.

The OB8's second page adds a lot of control and modulation extras. You could detune the VCOs in unison mode for a mega sound, quantise the LFO modulation into semitones, even put the LFOs out of phase with each other and set them to track the keyboard, so that the higher you played, the faster the LFO went — in a musical fashion too. There was a pair of software generated delay and attack envelopes for controlling LFO depth and frequency for anything from subtle expression to wild VCS3 impressions. These envelopes could be inverted for attack, hold and decay.

You could also mess with the portamento, choosing whether you wanted notes to arrive at the same time or not, pre‑programming slurs, and quantising to create glissando. Blind twiddling (my favourite form of editing) produced a stream of sounds that just seemed to spark the musical imagination.

The MIDI settings are also accessed from Page Two. You can select any MIDI channel from 1 to 8 as the basic channel, or opt for Omni mode if you prefer. When the synth is in split or layer mode you get true bi‑timbral operation, with MIDI data being sent and received on adjacent channels for each half of a split or layer. I must say that having each part of a layer responding to different MIDI channels can be plain confusing when used with a sequencer! A pleasant surprise, however, is SysEx, which allows patch dumping of the current patch via MIDI.

What is great about Page Two is that if you want to get on and play you can completely ignore it, but programmers can really dive in and have fun. Oberheim continually improved the software on the OB8, adding some features and debugging others. You can check the revision of any OB8 by pressing the Page Two button twice, holding it the second time, then pressing the sync button. The Programmer LEDs then show the version — B5 was the last.

The OB8 is the most modern‑feeling of the OB series, with features today's users expect, like programmable program volume, balancing of parts in a split or layer, and remembering many settings you had even after powering down. Like its predecessors, however, the OB8 lacked a touch‑sensitive keyboard. It still had a distinctive Oberheim sound, but one which I would describe as lighter than those of its predecessors.

Conclusions

The OB series are undoubtedly some of the great analogue synths, refined through their heyday from 1979 to 1985, and are probably the foundation of Oberheim's reputation today. The sound is big, bold, fat, and full. No doubt you have seen OB this or that in patch names on synths over the years, in the same way people talk of Moog bass, and although not as punchy as a Moog, for sheer power an OBXa or OBX is a valid alternative to a Memorymoog. As the series progressed, design and production improvements brought costs down, and improved reliability by using fewer actual parts inside, while increasing features and control with the clever use of software. The OBX, OBXa, and OB8 shared a similar voice architecture, which represented a frustrating mix of rash simplification and genius. Today this charms you and your creativity down interesting sonic avenues. If you are looking for an analogue synth, they are class acts.