SSM

SSM Analog Synthesizer Chips

Overview Dave Rossum's first silicon chip design achievements came in the analog arena rather than in the digital domain. Whilst Scott Wedge was programming the Eµ4060 Z80 software in 1976, Dave co-developed the first ever range of analog synthesizer chips with Ron Dow. The chips were manufactured by a local Silicon Valley foundry – Solid State Music (SSM). This range of SSM chips achieved considerable fame as the basis for a wide range of ground breaking synthesizers over the next few years, including the Prophet 5.

First Attempts In 1975 Ron called by the E-mu Systems office (house) in Santa Cruz and discussed a new VCA custom chip he was planning to manufacture, which had the potential of being utilised in E-mu's modular synthesizers. He was keen to get E-mu to buy in (literally), as he wanted them to stump up the US$1000 to integrate it! The idea was initially interesting until Ron explained that chips would work with power rails up to +/-12V. Since the E-mu modular systems were based on +/-15V this was a non-starter and Ron was shown the door!

Improved Designs A year later and Ron was back with an improved VCA design which had +/-15V power rails. This time Dave became interested! A loose co-development partnership developed over the next few years, with Dave contributing design ideas and providing Ron with lab equipment to perfect the design of the SSM2010 (low distortion VCA), SSM2020 (VCA) and SSM2030 (VCO). The SSM2030 was a lengthy year long and difficult project. It was followed by the SSM2040 (VCF) and SSM2050 (Transient Generator) which were largely Dave's designs. These innovative chips were all available by the early summer of 1977, making a new generation of synthesizers feasible in 1978.

Fathers of the Polyphonic Synth The range of SSM chips that Dave Rossum designed with Ron made polyphonic synthesizers possible. The availability of each analog building block on a single chip meant that multi-voice synthesizers were economical to build, and could be manufactured so that each voice sounded nearly the same. This was a big step forward from the expensive and huge Yamaha CS80 and Oberheim 8-voice of 1976.

The chips achieved considerable fame as the basis for a wide range of ground breaking polyphonic synthesizers including the Prophet 5 Revision 1, the PPG Wave 2.2 and the Korg PolySix.

Emulator Core E-mu Systems based a number of analog synthesizers of the late 1970's on the SSM chips, including the Audity, Galanti and Blue Box. They sold both individual chips and complete voice cards up until 1980/81. Later SSM chips featured in the warm analog VCF's of the early E-mu digital samplers and all the drum machines.

• SSM2020 (Dual VCA) - Audity, Blue Box, Voice Card
• SSM2030 (VCO) - Audity LFO, Blue Box, Voice Card
• SSM2040 (VCF) - Audity, Blue Box, Voice Card
• SSM2044 (LPF VCF) -Emulator, Drumulator, SP-12, SP1200
• SSM2045 (VCF/VCA) - Emulator II
• SSM2047 (VCF/VCA) - Emax
• SSM2050 (TG) - Audity, Blue Box, Voice Card

Most of the analog modules in the Modular were switched over to using SSM chips from 1977 - 1979. If you want more information on how these chips were used in the Modular click on the more.

• Resonant Filter - SSM2020
• High Pass Filter - SSM2040
• Transient Generator - SM2050, SSM2055
• VCA and Dual VCA - SM2010, SSM2020

E-mu Systems finally stopped using the SSM designs when supplies of the SSM2044 ran out in the late 90's, and they had to replicate the chip with discrete logic in the final run of SP1200's.

Competition The chips proved very popular from 1977 - 1985, with the only competition coming from Curtis Electromusic Specialities (CEM) based in Santa Clara, who began manufacturing a range of analog synthesizer chips in 1979. These proved to be rather more stable in design, but they did not have the warmth of the SSM designs. The Emulator III was the only E-mu design to use CEM chips (the CEM 3387).

Today The SSM analog synthesizer chips are now out of production and quite hard to locate new. The SSM2044 was manufactured up until the late 90's, but many others are over 20 years old. Some chips turn up as old synthesizers are broken for spares. The original chip designs are apparently lost, although it may be possible to reverse engineer them as they use a standard transistor base. SSM were taken over by Analog Devices, and some SSM designs are still in production including dual transistors and VCA's.

Some designers have started to duplicate some of these classic designs. At E-mu Systems Gary Hull replicated the SSM2044 for the last SP1200's in the late 90's, and there is a complete replication of the famed SSM2040 VCF in discrete transistor logic in a contemporary modular system.

SSM Voice Card

Overview Throughout the 1970's E-mu Systems supported the synthesizer kit community, helping enthusiasts who couldn't afford a retail synthesiser at US$2000+, but who could afford to spend a few hundred dollars putting together a kit of parts. The analog synthesizer modules in the Modular were available as pre-built sub-modules, without front panel controls and as a populated and tested PCB's.

E-mu Systems were able to go one step further in 1979, with the availaibility of SSM chips that miniaturised each synth module. Dave designed a complete monophonic synthesiser that fitted on a printed circuit card that was just 6" x 6.5". This card could be used by enthusiastic synthesizer builders to create a monophonic synthesiser or it could form the basis for a larger computer controlled polyphonic system.

We know of at least one musician who built an eight voice synthesiser using these voice boards, designing a modular like main system cabinet to hold them.

Voice Architecture The Voice Evaluation Board was a complete dual oscillator analog synthesiser, consisting of:

• Two VCO's using the SSM 2030, with PWM, linear and exponential FM, and hard sync.
• A single VCF using the SSM2040, which could be configured as high-pass, low-pass or phase shift.
• Two voltage controlled ADSR's, based on the SSM2050
• Two VCA's based on the SSM 2020
• An optional on-board power supply
• A 100-pin edge connector (S100 bus)

Revision 2 The Voice Card was updated to use the latest SSM chips, and later models used the SSM2033 and SSM2055/56.

Options The Voice Board came with user documentation and the schematics. It could be bought in three configurations:

• 1600K - Basic Kit with SSM chips and special components
• 1610K - Complete Kit with all components
• 1610 - Assembled Board, which has been tested

The Voice Board does not seem to have sold very well, and they are rarely seen on the second hand market. It was advertised in Polyphony, a US synth DIY magazine, and sold from 1979 - 1981.