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Oberheim TEO-5

Polyphonic Synthesizer By Gordon Reid
Published July 2024

Oberheim TEO-5

Far from being a cut‑down version of one of its bigger siblings, the TEO‑5 is a brand new Oberheim synth with a personality of its own.

Back in the not so dim and distant past, the engineers at Sequential took one of the company’s synthesizers — the Prophet 6, to be precise — and whipped out all of its voice boards. But, realising that a mute synth is only slightly better than a deaf sound engineer, they then inserted a bunch of different voice boards based upon Oberheim’s legendary SEM module, made a few other changes, and revealed a new instrument that they called the Oberheim OB‑6. I reviewed this in 2016, and was impressed. I had liked the Prophet 6, but I liked this more.

Let’s now fast‑forward to the present, where you’ll find me noodling around with a new Oberheim synth called the TEO‑5. At the time of writing, it hasn’t been announced, but a quick glance suggests that Sequential have pulled the same trick here as they did eight years ago. Just look at the chassis and control panel; the TEO‑5 seems to have the same relationship with the Take 5 that the OB‑6 had with the Prophet 6. But appearances can be deceptive. While there are similarities, even to the extent that the draft manual contains accidental references to the earlier model, don’t be fooled into thinking that they are different incarnations of the same underlying five‑voice polysynth. Sequential have no doubt saved time and money by re‑employing some existing tooling, but the two are distinctly different instruments.

The Voicing

Like the Take 5, the TEO‑5 uses a pair of SSI2130 analogue oscillators for each voice, but that’s where the similarities in the audio path end. Whereas the earlier synth used SSI2140 filter chips, the TEO‑5 offers a version of the state‑variable 12dB/octave SEM filter per voice. Furthermore, there’s nothing on its motherboard that looks like a VCA stage, so I contacted the chaps at Sequential, and they confirmed a growing suspicion: unlike the Take 5, there are no audio signal VCAs; loudness shaping is performed in the digital realm. This was not what I had expected and it means that, unlike some other polysynths that I’ve reviewed in recent years, removing the digital effects from the TEO‑5’s signal path doesn’t give you an analogue synth.

Both oscillators in a voice offer three waveforms — triangle, ramp and variable‑width pulse — and you can select any combination of these that you wish. PWM is obtained independently for each oscillator from the modulation matrix (see box) and you can select one or more simultaneous sources to control this. Osc 1 also features a square‑wave sub‑oscillator one octave below the selected pitch. You can tune each oscillator over a range exceeding five octaves, although I found that — perhaps unsurprisingly — MIDI note C5 wasn’t exactly five octaves above C0 on any of the voices in the review unit, and remained a few cents out no matter how many times I calibrated the synth. You can also detune Osc 2 for the usual rich, chorused effects. As you would expect, the cross‑mod lacks the consistency of a digital FM synth, but you can use cross‑mod and sync simultaneously to create sounds that you might not expect from an instrument of this nature. You can disconnect each oscillator from the keyboard and MIDI to use as a drone or, in the case of Osc 2, as a static audio‑frequency modulation source. You can also set the portamento time independently for each. In addition, you can send the output from Osc 2 directly to the amplifier, bypassing the filter. This is an old CS‑80 trick that allows you to reinforce the fundamental after heavy filtering, but is more advanced in the TEO‑5.

You’ll find the source mixer in the filter section. This only offers on/off buttons for the oscillators, the sub‑oscillator and your choice of pink or white noise, but you can set the levels for each in the Program menu. There’s no external audio input. The SEM‑inspired filter itself has bags of character. This isn’t surprising, because a quick inspection suggests that it’s based on the OB‑X‑inspired filter in the OB‑X8. However, like its forebears, you can’t force it to oscillate, even if you use multiple modulators to increase the amount of resonance. (I tried.) If offers four filter types, smoothly transitioning from low‑pass to notch to high‑pass, with an additional band‑pass mode available from the Program menu. You can modulate the filter type, cutoff frequency and resonance using the matrix.

The rest of the signal path for each voice comprises an A‑D converter followed by four digital stages. The first of these is the digital amplifier that performs the role of the audio VCA in a pure analogue synth. Following this, the signal reaches the first of three digital effect units. This is a simple overdrive that — far from generating the unholy rasp obtained from some earlier generations of digital distortion — can add a pleasing body and drive to your sounds. This is followed by an Effect unit (great name!), which allows you to select one of 12 algorithms — four types of delay, chorus, flanging, an emulation of the classic Oberheim phaser, a high‑pass filter, distortion, an emulation of the original Oberheim ring modulator, rotary speaker and ‘lo‑fi’, the last of which combines overdrive and wow/flutter to emulate a sickly tape machine. There are only three parameters to control each of these, and you adjust them using knobs called Time, Depth/Mix and FBack/Misc. For the most part, these names are descriptive of their functions but, were I ever to use the TEO‑5 in anger, I would print the parameter chart, laminate it and stick it next to the synth. Finally, there’s a dedicated reverb with controls for the mix, room size, pre‑delay and decay time, and a multi‑mode HP/LP filter to shape the reverberated signal. Having reached the end of the signal path, the audio is then converted back into the analogue realm before being presented to the audio outputs on the rear panel....

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