9090 Analog Drum Synthesizer

Update via joseph_amos in the comments: "This is actually a DIY project. [link] It looks like whoever is selling just copied and pasted the text from the first page. "

images via this auction
"serial No. 001 t page 2002
The 9090 is an analogue drum machine based upon the legendary Roland TR-909 Rhythm Composer. Many people consider this machine to be the life and soul of house music and it's modern derivatives. Trance, techno, whatever. In some moment of insanity back in '99 I decided it would be a fun challenge to build an entire clone of this classic analogue drum box (having no appreciation of how such a project can take over your life) and, bored with using sampled beats, I wanted a real, tweakable analogue box. Just like the 909.

I chose to make my 9090 just a MIDI controlled unit without an integral sequencer. All original drums are in there, together with power supply and a new PIC-based MIDI interface. The complete project is built across two separate printed circuit boards, designed to fit within a 2U height 19" rack enclosure. I didn't develop a sequencer to go with this, but I'll do it if I get the time.

The voice circuits used within the clone remain faithful to those of the original machine. In other words they remain mostly unchanged, except where I've added controls for extra tweakage. Most semiconductors have been substituted for modern equivalents that are more easily available. Most of the TR-909 sounds are completely analogue and hence some pretty intricate discrete circuitry is involved. Only the hi-hat and cymbal are 'digital' since the TR-909 used samples contained within three 32K ROMs for these.

The final version was built using nice professional printed circuit boards. I had a quantity of these PCB sets made and they are available to buy at 49GBP a set. These are completely blank PCBs only of course and almost everything else has to be obtained separately, but a PIC is supplied for the MIDI circuit and pre-blown EPROMs optionally be provided too for the digital sounds. The boards went through a few revisions before having the final PCB run so I am pleased to report that the boards are entirely error-free and no track modifications are needed.

Modifications
A small number of modifications were included to further enhance the 9090's capabilities, mainly in the form of extra potentiometers. The arrangement of knobs on the front panel is similar to that on the TR-909, but you can probably spot a few new ones on there.

In particular the versatile Bass Drum has several additional controls. Pitch sets the initial pitch. Tune Decay (formerly Tune) sets the speed at which the pitch is swept (lowered) as the drum sounds, and Tune Depth sets the sweep amount. Rotating the Tune Depth control clockwise produces a lowered final pitch. Manipulating the Pitch, Tune Decay, and Tune Depth settings can produce a bass drum ranging from relatively flat sounding, to a very energetic, punchy kick that really cuts through the mix.

A Bass Drum Distortion control causes an increasing clipping effect as it is rotated clockwise. This simple addition takes advantage of the diode clamp circuit that ‘rounds off’ the triangle wave from the VCO, by overdriving the diodes to produce a more square, overdriven sounding wave.

A Tune control has been added to the Hi-Hat voice. This affects both open and closed-hat sounds together. It works in the same way as the tune control for crash and ride cymbals.

Interfacing
The 9090 has a complete MIDI interface, implemented with a PIC microcontroller. Drum sounds are assigned to individual keys and are velocity sensitive. By means of a Configure button, MIDI channel and note assignment (how the drum sounds are assigned to various notes across the keyboard) can be altered using MIDI messages. A MIDI Thru jack allows chaining of further MIDI instruments via the 9090. A useful MIDI LED provides visual indication of all data, with the exception of clock information.

A handy MIDI to DIN Sync interface was included for good measure simply because I needed one to synchronise my TB-303 with the MIDI clock. Two DIN Sync outputs are located next to the MIDI sockets, providing a fixed 24PPQN signal.

Enclosure Design
The 2u enclosure is one obtained from Maplin Electronics here in the UK. The supplied front and rear panels were discarded in favour of some professionally made panels from Schaeffer Apparatebau in Germany, designed using Schaeffer's own free Frontpanel Designer software. The Alpha potentiometers are mounted to a sub panel inside, with the 16mm Re'an 'soft touch' knobs fitting through 17mm holes on the very front. I was a little apprehensive about how this would turn out, but fortunately everything aligns perfectly thanks to Schaeffer's excellent workmanship.

The rear panel looks kind of incomplete in these pictures because the rear individual output sockets have not been wired up properly yet. I'm going to get a PCB made to accommodate these sockets actually, because wiring all those resistors to them does look a bit messy IMHO.

Of course, the project could be built into a desk-top style case - this would be really funky if a sequencer was incorporated. The boards could probably be stacked if necessary, one on top of the other, with carefully chosen low-profile components. When mounted into a rack enclosure, the potentiometers can be mounted on the front panel in exactly the same order as those on the original machine, with the drum circuits arranged in the appropriate order to allow for this. Most potentiometer headers are located along the top edge of each PCB so that potentiometer wiring is kept relatively short."