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Oberheim OB-X8

Polyphonic Analogue Synthesizer By Gordon Reid
Published October 2022

Oberheim OB-X8

Oberheim are back, and doing what they do best — making massive polysynths with a massive sound.

Back in the distant past, I owned an Oberheim OB‑X. It was a bit tatty and wasn’t my favourite synth, so I swapped it at a famous London music store for a Prophet T8. With its wide, weighted, velocity and poly‑aftertouch sensitive keyboard, this was far more suited to my needs, so I never regretted the trade. Nevertheless, there was something a bit special about the OB‑X that I only appreciated when I no longer had it.

Later, the opportunity arose to obtain a museum condition OB‑8, so I did, but my retrospective lust for the OB‑X never quite faded. Wouldn’t it be nice, I mused, to have a synth that sounded like the OB‑X, but with all of the facilities of the OB‑8 as well as the keyboard from the T8? I waited for a few years, then another few, and then some more... and then I gave up. But then I learned of the OB‑X8, an 8‑voice analogue polysynth designed to emulate all of the original OB series and then add facilities that extend it in a sympathetic fashion.

When the review unit arrived, I immediately popped it on a two‑tier stand above my OB‑8 and switched both on. At that moment, and for the first time ever, the OB‑8 misbehaved and did something that I would never recommend — it took up smoking. So I contacted The Synthesiser Service Centre in London to arrange an emergency trip to the doctor. But one important lesson had already been learned. While we might revere our old synthesizers, owning them is as much an exercise in curation as it is in making music.

The 21st Century Oberheim?

Visually, the OB‑X8 recalls the OB‑X and the first model of OB‑SX rather than the OB‑Xa and OB‑8. It’s roughly the same width as the OB‑X and, although it’s less deep, the controls are laid out much as before. Consequently, and despite the addition of a small OLED screen and its associated encoders, there are wide spaces between the knobs and buttons that might feel odd to players accustomed to the dense panels of some modern instruments.

As in all previous OB‑series synths, there are two VCOs per voice. At some point, it must have been decided that the discrete OB‑X oscillators were superior to the CEM3340s in later models so, unlike elsewhere in the OB‑X8, there are no OB‑Xa and OB‑8 options. This means that what we have here are OB‑X oscillators with additional OB‑8 facilities; simultaneous selection of the waveforms, independent pulse widths for osc 1 and osc 2, a triangle wave and semitone tuning for osc 1.

Cross‑modulation is implemented as it was on the OB‑X. This means that there’s no way to adjust the amount, although you can now select whether either or both of osc 2’s sawtooth and triangle waves are used as the modulation source. In addition, there’s hard sync, and the filter contour can sweep the frequency of osc 2 as it could on the OB‑Xa and OB‑8. You can engage cross‑mod and sync simultaneously, but the OB‑X8 remains surprisingly well behaved when you do, and doesn’t descend into weird and wacky territory.

The outputs from the oscillators pass to the single filter per voice. This is perhaps where the OB‑X8 will find greatest favour with purists because the 12dB/oct SEM‑style OB‑X filter and both the 12dB/oct and 24dB/oct modes of the CEM3320‑based OB‑Xa and OB‑8 filters are available. In addition, the high‑pass, band‑pass and notch modes from the original SEM filter are provided, which means that the OB‑X8 can make more than a passing stab at emulating the fabulous but unwieldy Oberheim 8‑Voice.

On the OB‑X, there were five buttons controlling the audio inputs into the filter: osc 1 at full level, osc 2 at half or full level, and noise at half or full level. The OB‑Xa and OB‑8 lost the half‑level noise button, and now there are just three — osc 1, osc 2 and noise — and you use the menus to determine the signal level for each of these sources.

Cutoff frequency and resonance knobs are provided, and a dedicated ADSR contour generator performs shaping duties. None of the original OBs offered self‑oscillating filters, and so it is here; the resonance can be pronounced, but it never strays into oscillation. Keyboard tracking is also available, and you can adjust this from zero to 100 percent. The output from the filter then passes to the audio amplifier, the gain of which is controlled by its own ADSR contour generator. At this point it’s worth noting that there were differences between the contours generated by the OB‑X/Xa and the OB‑8, so the OB‑X8 allows you to select the characteristic that you prefer in any given patch.

The OB series had a single, global LFO rather than one per voice. Again, the different characteristics of the vintage models are accommodated and, depending upon which you choose, several underlying attributes are changed. As on the OB‑8, you can choose from seven waveforms, with an option to select between the OB‑X/Xa’s sine wave and the triangle wave that replaced it. However, the OB‑X8’s panel only offers access to five of these, with the key‑sync’ed triangle wave and the unusual Sampled Vibrato LFO wave accessed through the menus alongside things such as LFO sync, tracking and phase. The LFO’s maximum depth is that of the OB‑8, as is its frequency range of approximately 0.07Hz to 50Hz, both of which exceed the narrower ranges of earlier models. The range of LFO destinations is tiny by modern standards, with the chosen waveform directed at one depth to the frequencies of osc 1, osc 2 and the filter cutoff, and at another to the pulse widths of osc 1 and osc 2 and the gain of the audio amplifier. You can switch the modulation path on or off for each of the destinations, but that’s all.

In addition to the master volume and tune, the Master panel contains the Volume/Balance knob, which allows you to program the patch volume or the balance between the Upper and Lower parts in a Split or Double (see below). There are also three buttons. The first (Tune) does what you might suspect — it tunes and scales all 16 VCOs. The second (Hold) latches any notes being played while you depress it but, once it’s released, allows you to play any unallocated voices conventionally. The third (Chord) allows you to save a held chord and then replay it at any pitch. You can define how the chord is held (keyed or infinite) and the range over which the function operates. Unlike the vintage models, chord triggering is now handled correctly and the generated notes can exceed the highest pitch available from the keyboard. Again, you can play any unused voices conventionally.

The Control panel contains two important sound generation controls alongside some of the performance controls. These are the osc 2 detune knob and the Vintage knob that determines the amount by which the oscillators, filters and contours can differ across the eight voices. A third knob controls the portamento time. But...

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