Doepfer MS-404

In December 1994, Doepfer released the Doepfer MS-404
The MS-404 is a MIDI analog synthesizer with a 24db resonant filter that Dieter Doepfer intentionally created for his own personal pleasure earlier that year.

MS-404 close-up - Picture via Matrixsynth

In the summer of 1994 he created a monophonic analog synthesizer in a 19-inch rackformat / 1 unit high.
Although his module could do so much more than reproducing the sound of a TB-303, most consumers looked at it as an extended clone of the classic Roland TB-303 bassline.

Its two LFOs (that can modulate the single VCO) add a lot extra to the original 303 functionality.
Other extra features include a full ADSR envelope generator, noise, FM and PWM capabilities, an external filter input, CV/GATE interfaces, MIDI implementation and a glide effect.
The MS-404 can be played via MIDI but all parameters are controlled manually only.
The slide and accent effects from the TB-303 are possible on the MS-404 via glide control and it uses MIDI velocity for accent.

MS-404 Picture via Matrixsynth

The price was around 300 Euros (598 DM) and the module was released in a time when the demand for 303-clones was huge and many different manufacturers were building those; Future Retro 777, Syntecno TeeBee, Control Synthesis Deep Bass 9, and MAM MB33 were  few competitors, to only name a few. (A large list of 303-clones can be found on Wikipedia)

In the beginning Doepfer only planned to launch 50 to 100 modules, but they received almost 500 orders in the first two months in 1995.
At the end of 1997 Doepfer had sold more than 3000 MS-404 units.
The last MS-404 was sold in March 2001, as the amount of inquiries was falling (from 100 items per month to hardly 10 items per month at the end of 2000).

The few differences between the 2 regular versions of this module are minor.
There were always rumors that the different versions of the MS-404 sound different, but there were never any changes in the MS-404 hardware.
Version 1 can not use MIDI sustain, but this doesn't have any effect on the sound.

The rare green version of the MS-404
(Picture via Marc C Young)

In 1997 approximately 100 limited edition synths (with a green faceplate and a printing 'Music Store') were sold as a 25th anniversary special for Music Store of Cologne, Germany.

Doepfer still offers technical support for the unit and the manual is still available online.

Video: Doepfer MS-404

" Smooth synthpop demo made with the Doepfer MS-404.
This is really a little 1 VCO beast. Multitrack + external FX. "
Uploaded by SyntheticMachines

More:
http://www.doepfer.de/ms404_e.htm
http://www.vintagesynth.com/misc/ms404.php
http://en.wikipedia.org/wiki/MS-404