Sequential Circuits Model 800 Digital 256-Step Sequencer SN 0330

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" The Sequential Model 800 Sequencer is a 256-event cv/gate sequencer based on microprocessor technology. This was probably Sequential's first product. Dave Smith started making these units in his garage. A cv/gate sequencer based on microprocessor technology. First known product from Sequential Circuits. Less than 500 units were produced between 1977 and 1980 starting in Dave Smith's garage.

This is serial number 0330, and was recently refurbished by synth maestro Dave Brown at Modular Synthesis.

He did an incredible job, which you can see at this page documenting the repair and restoration

This SCI 800 is described at the bottom of the page (the top of the page is my other, much earlier SCI 800, that truly proved a challenge to reverse engineer and fix!)

It was built like a tank, encased in a 8"X10"X5" metal box. It represents one of the first attempts at a commercial meld between analog and digital technology.

The 800 consists of 16 toggle switches which enable "cells". Each cell can hold up to 16 note-events each. The cells are loaded from CV (control voltage) keyboard via the CV/gate inputs (1 volt per octave) and can be programmed over a 5-octave range. The Gate is switchable between S-trigger and voltage gate. An internal clock runs from 20Hz up to 5kHz to calculate absolute note length or beat division if being driven externally by a low frequency clock. External input is provided via a specially wired plug. A multi-pin parallel connector is used to hook two or more 800's together. A foot-pedal was available for toggling between record and play modes and start/stop. The CV/gate output is quantized to semitones (1/12). The gate can also be switched between S-trigger and voltage gate.

Sequences cannot be stored, however there may have been a battery backup modification. If a hi freq VCO is used to "clock" the sequencer, it can function as a crude audio waveshaper.

The Model 800 can hold up to 256 events. There are 16 switches which enable "cells", which can each contain 16 events. They are loaded by an external CV keyboard and can be programmed over 5 octaves. An internal clock running between 20Hz-5kHz calculates the absolute note length or beat division when driven externally by a low frequency clock.

Multiple M800s can be hooked together with a multi-pin parallel connector. A foot pedal was made available to cycle between record and play modes. The cv/gate output is quantisized to 1/12 semitones. User sequences can not be stored, although there are rumors about a battery backup modification.

The Model-800 is a digitally controlled step sequencer. However, you'll notice that there are a lack of knobs (other than for tempo). Instead of 'dialing in' each note via a pot, and then being stuck with an 8-note-to-the-bar sequence, it records CV and gate voltages in real time. You can play at any speed, with any syncopation, and with any note lengths. It can record up to 256 notes, and you can edit note pitches and durations. That's right, real time digital sequencing in 1977.

The Model-800 has ample jacks for external clocking, chaining multiple Model-800s together, and separate CV sources for input and output. The jack labeled 'Trigger In' should really be labeled 'Gate In'. The Model-800 records actual gate-on time, and doesn't just record the trigger event.

There is also a foot pedal jack, for hands-free operation of the controls.

Model-800 Rear Jacks
◾External Clock In
◾External Clock Chain Out
◾Trigger In
◾CV In
◾Trigger Out
◾CV Out
◾Foot Pedal

Before MIDI came along, interfacing synthesizers together from competing manufacturers was not straightforward. Each brand used variations on gate voltage and polarity, CV voltage range and scaling, and gates vs. triggers.

The Model-800 has several toggle switches on the back panel to correspond with the most common settings. Here is a table from the original owners manual, showing how to set things up for various synths.

The Model-800 has 16 memory banks, which can each hold up to 16 notes. You can enable or disable the memory banks with toggle switches on the front panel. This allows you to have multiple sequences in memory at the same time, or protect a sequence from erasure. You can also perform minor arranging as a sequence is playing, by enabling and disabling memory banks in real time.

Once the memory banks have been selected, you can step through the individual notes using the Step and Reset toggle switches.

These functions are used mostly for resetting the sequence for playback or record, or for editing individual notes.

Recording on the Model-800 is fairly simple. You select the memory banks, reset to the beginning of the sequence, press the record button, and start playing.

Playing back is easy as well. You select the memory banks, reset to the beginning of the sequence, and turn the clock on. At the end of the sequence, it will automatically reset to the beginning, and play back in an endless loop.

Finally, there are toggle switches on the front panel that can enable or disable recording of the pitch CV, and also record a single note (with the clock disabled). These can be used to edit the pitch or duration of a single note."