Home
Analog Articles
Manuals
Synth DIY
Site Overview
 

Index
ARP 2500
ARP Filters
ARP Quadra
SCI 700
SCI 800
Oberheim OB1
Roland Seq'rs
Roland 700

 Email me

Created by
 Western Graphics
Last modified
 08 February, 2006
 

Sequential Circuits
Model 700 Programmer

Overview Back in 1974 Sequential Circuits was a small music technology company based in San Jose, California and run by Dave Smith from his apartment. The initial product was the Model 600 analog sequencer, followed in late 1975 by the Model 800 digital sequencer. Dave and new recruit John Bowden (x-Moog) then went on to create the Model 700 Programmer in the spring of 1977.

The new product provided rudamentary patch memories for analog mono-synths like the Mini-Moog and ARP 2600. The table top programmer had 64 memories of 3 control voltages to drive the VCO's and two DADSR envelopes to drive the VCF and VCA of the partner synthesizer. In 1977 this was a major step forward, with only Oberheim providing patch memories on its 4 and 8 voice synthesizers. The Model 700 makes use of CMOS digital chips and early RAM chips, Dave didn't use the newly available Z80 microprocessor. That would have to wait until the design of the Prophet 5  later in 1977 and the influence and support of Dave Rossum at E-mu Systems.

Mark 1 Dave launched the Model 700 in early 1977 and went on to sell one a week, mainly in the USA, for a few years. Here is a Mark 1 model, all the knobs are large, there are no CV trimmers on the top left hand panel and the patch switches are engraved with numbers. The record switch is part of the right hand lower toggle switch..

Mark 2 In 1979 the Mark 2 model was released with front panel V/octave trimmers for the 3 control voltages, and a single multi-way socket for a single cable connection to the partner synthesizer. The Mark 2 has revised PCB's and a slightly different circuit design. The original CA3080 and matched transistor design was updated to use SSM2050 and SSM2020 chips, along with TL072 Op Amp's. The high quality sealed cermet pots were also replaced with standard carbon pots. All these changes meant the Model 700 could be manufactured for less money.

Sequential Circuits went on to sell over 200 Programmers, and it was still in the catalog in March 1981.

The Model 700 has a place in synthesizer history and it provided some funding and technical R&D for the legendary Prophet 5. Below is a Mark 2 version with Prophet 5 knobs, and lettering above the tactile switches. The 7 segment display is larger and the patch Record facility has a red button rather than being on the right hand lower toggle switch.

Description The Model 700 has 3 independent control voltages for controlling the pitch of the partner synthesizers VCO's. Each pitch is controlled by a rotary potetiometer, and a single external control voltage from a keyboard can be optionally added into each pitch with 3 toggle switches. The pitches are quantized to semitone values.

Two envelopes can be programmed with the usual ADSR and an initial delay - very Dave Rossum! The envelopes are triggered from gate or trigger inputs, usually from the external keyboard. The envelopes are designed to drive the VCA and VCF of the partner synthesizer directly. Each envelope has its own VCA so that the envelope volume can be controlled from the 700. There is an additional offset control for envelope 2, so that the initial VCF cut-off can be set too.

Memories Once a patch has been set up with the programmer you can store it into one of 64 memory locations, selected by 8 switches (Programs) and a rotary switch (Banks). A red Record button is partially sunken into the control panel, which means it is not accidentally pressed. Patches can be recalled or the programmer can simply by used as a live set of controls.

Tricks The 700 has a few neat tricks up its sleeve. The 8 Programs within any Bank can be incremented electronically from a footswitch or a LFO or keyboard. Using an external LFO you can create a traditional 3 control voltage x 8 step sequencer with different VCF/VCA sounds for each step. The number of PRograms that are incrementade can be adjusted from a rotary front panel control from 0 - 8. When set to 3 the Model 700 will switch Programs as 1-2-3-1-2-3-etc.

Technology The Model 700 is based around CMOS logic chips, there is no microprocessor as the new Zilog Z80 was too expensive to use. Dave couldn't use ADC chips either, so he emulated one with discrete digital and analog chips. The control voltage resolution is 6-bits, which for the VCO controls equates to 64 discrete voltages, 5 octaves from 0 - 5V. However the envelopes also get the same resolution, which is a bit more of a limitation.

Inside there are two neat and well laided out PCB's stacked on top of each other. The first board contains 16 pots which are scanned and stored as 6-bit digital words into 768 bytes of SRAM storage, which is backed up by a 3V lithium battery. This data is used to drive the 3 control voltages, and to control two DADSR envelopes based on SSM2050's, along with two VCA's built from SSM2020's. This design is very similar to the Dual Transient Generator made by E-mu Systems.

* Analog Synthesizer Patch
   Programmer
* 64 non-volatile memories
* 3 control voltages (VCO's)
* 2 DADSR envelopes
* 2 internal VCA's
* 768 bytes of RAM
* 2 digit LED display
 

Mark 1
* Launched in 1977
* Based on CA3080 chips
* Patch buttons numbered

Mark 2
* Relaunched mid 1979
* Redesigned with SSM chips
* Larger 7 segment LED
* Prophet-like knobs
* Separate record button
* Trimmers for V/oct
* Single interface connection
 

* SCI Model 700
     Brochure      (1.6MB)

  Purple
  White
  Biege
  Orange
  Green
  Yellow
  Red
  Black
  Blue
  Green
  Orange
 

Envelope 2
Envelope 1
Voltage 3
Voltage 2
Voltage 1
External Voltage
Trigger
Gate
Switch Trigger

Program Increment
 

The Model 700 originally sold for US $995, from 1977 - 1981.

Over 200 were manufactured in San Jose, and the build quality is consistently high. There are some minor kludges on the PCB's.

Model 700's do occassionally come up second hand, but condition is very variable from mint to write-off. Secondhand prices vary from $50 - $200.

Repairs are generally easy, but watch out for the rare 1kx1 SRAM chips, which are $17 each to replace.