SSM2040

The SSM2040 IC is a 4-pole filter from Solid State Micro Technology For Music (SSM). Regarded as one of the best sounding filters, because of the way resonance and small amounts of soft distortion when overdriven, can add harmonics to the original signal.

History

Designed by Dave Rossum of E-mu Systems and used in the first 2 versions of the Sequential Circuits Prophet 5. Early SSM chips were often defective, and having to pay royalties led Sequential to switch to Curtis ICs in later versions of the Prophet 5.

Circuit building block

The device's cutoff frequency can be exponentially voltage controlled over a 10,000 to 1 range. It is an extremely flexible circuit building block which can be used in virtually any active filter design including low-pass, high-pass, band-pass and notch. Roll-off characteristics can be selected to be Butterworth, Chebyshev, Cauer, Bessel or any other filter type.

Clones and schematics

In chronological order:

• discrete SSM2040-style filter by Jürgen Haible, 1997.
• SSM2040 Style 4 pole Filter by Jürgen Haible, 1998. A discrete version that reproduces the original sound. A lot of component selection is needed (matching transistor pairs). The circuit is not a pin for pin replacement, and it has a voltage controlled resonance path added. There'a little error in the drawing: the pnp current mirrors have C and E mixed up.
• SMD SSM2040 filter by René Schmitz, 1999
• 4-pole VCF by Osamu Hoshuyama, 2002
• The SSM2040 Integrated Circuit, by James Gideon, 2006
• SSM2040 style VCF + discrete VCA (AMORE), 2011. Both circuits by René Schmitz.
• Discrete Transistor 2040 SVVCF by Scott Stites, electro-music.com forum, Apr. 2013

Synthesizers etc. using the SSM2040 or clone

• AMSynths AM8040
• Digisound 80-7. In 1982 this was replaced by the CEM3320 based 80-7A which offered the same features but with "lower noise and improved resonance level".
• Division 6 Filtare SEIII
• E-mu Systems Blue Box and Audity
• E-mu Systems SSM Voice Card
• Hearn Morley HM2040 potted module.
• Mad Science Lab SSM2
• Mattson Mini Modular FV1-B, based on the SSM2040 designed by Jim Patchell
• Radio Junk Box 2040 VCF
• RSF Kobol Expander I
• Sequential Circuits Prophet 5 Rev. 1 & 2
• SMB-1 Project
• SRM Synthesizer Octave Cat
• SSM2040 VCF by Ryan Williams, March 2007.
• Steiner EVI
• Synthesis Technology MOTM-440
• Tiptop Audio Z2040
• VCF/Phase Shifter by Craig Anderton, AMS-100 guitar processor, Device 6, 1979
• Vedic Scapes Model 2040, uses the HM2040
• Voltage Controlled Phase Shifter module by Craig Anderton, AMS-100 guitar processor, Device 4, 1979

See also

• CEM3320
• SSM2044
• SSM2045

Further reading

• SSM2044 data sheet
• Build a better music synthesiser by Thomas Henry, Tab Books Inc, 1987, ISBN 0-8306-2753-3, Chapter 6: A four-pole lowpass VCF – SSM2040
• Electronic Music Circuits by Barry Klein, Howard Sams, 1982,ISBN 0-672-21833-X, pages 125-126, 135-137, 141
• Two ICs For Electronic Music – SSM2020 And SSM2040 by Dave Rossum, Electronotes 78, Volume 9, 1977, p. 15
• Reader's Circuits – VCF With SSM2040 by Rich Ryan, Electronotes 84, Volume 9, 1977, p. 17
• A Fourth Order State-Variable Filter by Bob Chidlaw, Electronotes 99, Volume 11, 1979, p. 3
• Musical Applications of Microprocessors by Hal Chamberlin, Hayden, 1985 ISBN 0-8104-5768-7, pages 218-220, 599, 603
• The Smooth Phaser by Thomas Henry, Electronic Musician, June 1988, pp. 78, 80-83.

External links

• Circuit for dynamic control of phase shift, US Patent US3969682, by David Rossum, 1974
• SSM2040 data sheet at MaxMidi Rare Silicon or Digisound80.co.uk
• The SSM2040 Integrated Circuit, by James Gideon, 2006. Discusses the IC, the ways it can be configured and the discrete version by Jürgen Haible.
• Additional Design Ideas For Voltage-Controlled Filters by Bernie Hutchins, Electronotes 85, Volume 10, 1978, p. 5
• SSM2040 VCF by Ryan Williams, March 2007.

Projects

• Build the PGS Lowpass Voltage Controlled Filter, Common Mode, January 1983, Number 1, pp. 10–15
• SSM2040 style VCF + discrete VCA (AMORE), 2011. Both circuits by René Schmitz.
• Synthesizer Phase Shifter by Thomas Henry, Polyphony, October 1984, pp. 14–17.
• Discrete Transistor 2040 SVVCF by Scott Stites, electro-music.com, Apr 2013