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Sequential Trigon-6

Polyphonic Synthesizer By Gordon Reid
Published October 2023

Sequential Trigon-6

Dave Smith’s last synthesizer is a worthy farewell from a man who gave the synth world so much.

Sometimes living people feel constrained to write nice things about dead people for no reason other than that they’re dead. I’m not one of them. As far as I’m concerned, an old bugger who has died is just a dead old bugger. I’m telling you this so that you’ll have context when I say that Dave Smith — the founder of Sequential — was one of the nicest blokes you could ever meet. That he was also a brilliant engineer who gave the world some of its finest synthesizers and was instrumental in the creation of MIDI was just another facet of the man. So it was with huge regret that, having planned to meet him at NAMM last year, the first newsflash that I received when I landed at Santa Ana airport was to learn of his death. Never again would I have the opportunity to ask him when he was going to fix my Rev 1 Prophet 5, only for him to repeat our long‑time ritual of telling me, most politely, to get lost. I will miss him, as we all should. At the time of his death, Dave was working on the Trigon‑6, which was announced later in the year. Now described by Sequential as the company’s “polyphonic take on the classic, thick and creamy analogue sound that defined the dawn of the synth era”, I wonder whether it’s a fitting tribute to the man and his achievements. Let’s find out.

The Technology

Whether packaged as the original Trigon‑6 keyboard or the recently announced desktop module, the Trigon‑6 is a 6‑voice, monotimbral analogue polysynth based upon three oscillators and a ladder filter per voice. The former makes it unusual, because the majority of polysynths rely upon two oscillators per voice. Nonetheless, it’s clearly a member of a family that includes the Prophet 6 and the OB‑6 and, like its siblings, is based upon six voice cards inserted into a motherboard that provides common facilities and housekeeping functions.

Each of the three oscillators in a voice offers sawtooth, pulse and triangle waves, with an additional ramp wave on osc 3. With exception of osc 3’s mutually exclusive saw and ramp waves, you can select any combination of these that you wish. Each oscillator also offers five octave settings, with detune of up to ±7 semitones on osc 2 and osc 3, hard sync of osc 2 to osc 1, an LFO mode on osc 3, and the ability to disconnect osc 3 from the keyboard CV and MIDI notes. White noise is provided by a separate noise generator.

The output from each voice’s oscillator section passes via a mixer to its Moog‑inspired low‑pass, resonant ladder filter. This offers 12dB/oct and 24dB/oct modes and responds like many such filters from the 1970s; as you increase its resonance, it passes less and less of the low frequencies presented to its input, creating a quasi‑band‑pass response at high values. I have always favoured synths that retain their welly when the resonance is cranked up, but I know players who prefer this response, so I’ll leave it to you to judge whether it’s a good thing or not.

The filter will oscillate at maximum resonance in either mode, and will track the keyboard at 50 or 100 percent when asked to do so. With tracking of 100 percent it will — unless confused by enharmonic pitches — lock to the oscillators, so you can use it as a fourth chromatic oscillator. If there’s a shortcoming (and it’s a common one) it’s that the resolution of the cutoff frequency knob is quite coarse. This may not bother you, but it’s worth noting nonetheless.

Lying in the oscillator section, there’s a knob that I haven’t yet mentioned, which is labelled FDBK <> DRIVE. Turned clockwise from 12 o’clock, this increases the oscillators’ output to overdrive the filter input. When turned the other way, it routes each voice card’s output back into its filter input, thus replicating the trick that we all used to fatten up the Minimoog — but here done polyphonically on a voice‑by‑voice basis. The results can range from warmth to chaos — you choose.

The output from the filter passes through an amplifier before being presented to two 24‑bit/48kHz digital effects units. Effect A offers two sync’able delays, a chorus, three phasers including an emulation of the original Oberheim phaser, an emulation of the Oberheim ring modulator, and two flangers, while Effect B adds four reverb emulations to these. Each effect algorithm offers just two parameters, so it’s unlikely that any of them will replace your expensive studio devices when recording, but the programmed effects are stored on a patch‑by‑patch basis so, for sound design and live performance, they work well. Nevertheless, if you’re a fanatic, switching both effects off takes them and their associated A‑D and D‑A converters out of the signal path, so your sounds can stay in the analogue domain until they reach your digital mixer, or MP3 converter, or CD recorder, or are uploaded to YouTube... or whatever.

Shaping and modulation are grounded in the 1970s. The two contour generators — one dedicated to the filter cutoff frequency and the other to the audio signal amplifier — are conventional ADSRs. The global LFO generates six waveforms (yes, I know that only five are shown on the panel), offers eight destinations, can be sync’ed to master clock or MIDI, and can be key‑sync’ed if desired. Polyphonic modulation is...

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