At the moment, there's a lack of real drum synthesizers in the Linux Audio
world.
Drum synthesis instead of sampling is important to emulate the dynamic sound
of -for example- the TR-909 hand clap, which is generated out of white noise.
You can find some patches for Alsa Modular Synth here:
https://sigterm.demon.nl/~stanley/drumsynth/
Most patches don't sound like the real 808/909, because they need some/much
more tweaking. Feel free to improve the patches.
I'm now trying to decipher the original schematics of the TR-909, my aim is to
write a separate 909 softsynth (clone), because Alsa Modular Synth is too
limiting (difficult/impossible to create drum maps, difficult to handle
multiple instances of AMS, etc)
Regards,
Stanley Jaddoe