On this page you will find all you need for building your own tr909 bass drum circuit (PCB, schematic,
This PCB was inspired by Colin Fraser, who found some very useful extensions to the bass drum circuit of the Roland TR909. Trevor page's 9090 - project was of course also very helpful for me !
As an addition to these modifications, I added a "compression" pot, changing the behaviour of the envelope of the tri/sine signal a bit, see schematics for detail. As it is a standalone bass drum, I added the noise circuit on the board. Noise is adjustable from 0% to maximum, unlike in the original TR909.
Here you will find a PDF-file, containing the PCB of the tr909 bass drum circuit (component side view !!!!) and 3 pics for component placement : I divided these into : Pots, Resistors and all the other things (for a better view). The transistors are depicted as they are built into the PCB, "5" means BC559, "4" means BC549. All Diodes are 2N4148. In my projets I allwys use 1% metal film resistors.
Schematic, klick on the thumbnail to get the high resolution image.
This is how two of these circuits fit into my MOD2...
...and of course, how it sounds. As you can hear, the PCB works fine. (in this case, I triggered the two 909-bass drums with my
16 step trigger sequencer.)