Zoë Blade's notebook

Sequencer Complement

The Sequencer Complement was an analogue step sequencer released by Moog in 1969, as part of the 900 Series of modules. The complement consists chiefly of three modules that work together: the 960 Sequential Controller (the sequencer itself), the 961 Interface, and the 962 Sequential Switch.

960 Sequential Controller

The 960 Sequential Controller was designed by Bob Moog and implemented by Moog engineer Gene Zumchak.[1] It was heavily based on Buchla's Sequential Voltage Source Model 123,[2] basically adding a built-in clock (a simple pulse wave LFO), and a little complexity to the step incrementing options.

This was quite the self restraint, considering that Bob Moog had already helped the notoriously secretive Raymond Scott transistorise his own earlier sequencer,[3] and by this point was aware of Scott's Electronium, which included a much more advanced sequencer, capable of transposing and otherwise modifying its patterns.[4]

Like the 123, the 960 offers up to eight steps, each of which outputs three different voltages at once. The step can be incremented (and finally looped back to the beginning) via a trigger, such as from an LFO. Each step has a button that allows you to jump straight to a particular step, and a gate output. Each row has a pair of CV outputs.

It differs from the 123 by replacing the switch that selects the number of steps with nine separate switches, one per step plus one at the end, that optionally lets it be skipped or stops the sequencer incrementing at that point. (This is arguably a tad overengineered. Indeed, Roland's later 104 and 182 sequencers pare this idea back a bit, bringing back the 123's pattern length switch and simply adding another switch to toggle between looping and one-shot operation.) The 960 also adds a button to manually increment the step; an input as well as output gate for each step, allowing automated random access; and a switch that optionally lets the third row's voltages affect the clock's speed.

961 Interface

The only issue is that the sequencer's gates are all of the sensible V-trig kind, whereas the 900 Series's keyboard, ribbon controller, and envelope generator all use the more obscure S-trig kind. This is where the 961 Interface comes in, translating between the two gate types, and converting audio into V-trig to boot — perfect for synchronising to other instruments, or adding a swung or otherwise humanised groove.

Quite aside from enabling the envelope generators to be controlled by the sequencer, the interface also allows them to be controlled by the vast majority of MIDI to CV converters, almost all of which use V-trig. This saves you from having to find an especially versatile converter that also supports the rarer S-trig. Even if you already have such a thing, it still saves you from fiddly menu diving within it.

962 Sequential Switch

The real improvement over the 123 is the addition of a separate module, the 962 Sequential Switch. By patching the sequencer to it just right, it can effectively work in a series rather than parallel fashion, so that instead of getting 8 sets of three control voltages, you can instead get 16 or 24 control voltages, allowing longer if simpler patterns. It achieves this by simply taking it in turns to pay attention to each one of the three outputs, or by alternating paying attention to the first two while the third is routed elsewhere. (Roland pared this back in their later sequencers too, simply having two instead of three rows, and adding a switch to toggle between parallel or serial operation.)


  1. "'It was a pretty straightforward digital project,' Gene remembered. 'I didn't have to invent any of the functionality of it; Bob defined the functionality and I simply implemented it in digital silicon." Switched On: Bob Moog and the Synthesiser Revolution Albert Glinsky, 2022, ISBN 978-0-19-764207-8, p. 158
  2. "Gene Zumchak, a Moog engineer, developed the Moog sequencer in 1968, but the idea was based on what Buchla had done." Analog Days: The Invention and Impact of the Moog Synthesizer Trevor Pinch & Frank Trocco, 2002, ISBN 0-674-01617-3, p. 336
  3. "Refining the Electronium concept remained Scott's primary focus throughout the 1960s, when integrated circuits made smaller and more efficient versions possible. He asked Bob Moog to 'sophisticate my equipment. The concept is the same as I've had for many years now. And you're the scientist who will make these things small, more compact, and with fewer parts.' Scott replaced his eight-stage 'sequential timer' relays with Moog's electronic stepping switches." "The World of Sound: A Division of Raymond Scott Enterprises" Jeff E. Winner, Sound Unbound: Sampling Digital Music and Culture, 2008, ISBN 978-0-262-63363-5, p. 195
  4. "Back to Bob Moog — he is a most honorable person. He steadfastly refrained from embodying my sequencer in his equipment line until the sheer pressure of so many manufacturers using the sequencer forced him to compete. Yet, he used the simplest version, though he knew about my most advanced sequencer. Quite a gentleman, and a super talent besides." Raymond Scott: Artifacts From the Archives Raymond Scott, 2017, pp. 13—14

5U: 900 Series (Moog) | Sequencer Complement | The evolution of the 900 Series

Modular synthesisers: 100 Series (Behringer) | 900 Series (Behringer) | 900 Series (Moog) | A-100 | Concussor | Sequencer Complement | System-100M | The evolution of the 900 Series

Analogue step sequencers: 100 Series (Behringer) | 900 Series (Behringer) | Sequencer Complement | System-100 | System-100M

Moog: 900 Series (Moog) | Bob Moog | Bode Frequency Shifter | Sequencer Complement | The evolution of the 900 Series