Sequential TOM Mini Cartridge


The TOM was one of the last products made by Sequential Circuits (in their original incarnation). For a 1985 drum machine, it has a lot of tricks up its sleeve, such as changing the pitch, volume and panning of sounds as part of a sequence, playing sounds backwards and time correcting all the way down to 96th notes. Not to mention it has a mode where every sound gets its own dedicated MIDI channel and can be played chromatically on the keyboard.

The built in sounds are quite good - they sound similar to the Oberheim DMX, but there aren't many of them. Sequential conveniently put a cartridge slot on the machine for adding additional sounds, but these cartridges are hard to find and expensive, and didn’t really interest me in terms of the sounds they offer. I came up with this small and simple little board which can take a single 27256 EPROM so I could play around with some new sounds.

New Sounds

Sounds on the TOM use the same mu-law compressed format used by the LinnDrum, DMX, etc., so you can use sound data from those machines more or less unchanged. All sounds are stored on one or two 32K EPROMs (I only used one for this design), and have a header block at the beginning that tells the machine how many sounds there are, how long they are as well as a few other things.

Following Bob Grieb’s superb reverse-engineering notes on the TOM, I wrote a generic header table that you can use. It expects 7x 4K sounds. To make your own ROMs, put the 4K header block at the beginning and then add 7x 4K sounds of your choice, one after the other to fill out the whole 32K. You’ll probably need to replace the first 8 bytes of each sound (except the first) with $00, otherwise you’ll get a lot of unwanted clicking after the sound has played.



Espen Kraft demonstrates using the cartridges in the context of tracks