subatomic wrote:when I had trouble with my 9090 snare r@f's page was a huge help.
(For example, here's his breakdown of the 909 bass drum)
he breaks down each 909 circuit and shows where the env/vco/vca/etc... are. makes it easy to understand each circuit.
especially useful for troubleshooting...
also, look for DC voltages that shouldn't be there, could mean you have a trigger stuck "on", or if you have the wrong type (npn vs pnp) transistor in, it might be shorting the trigger to ground making the trigger do nothing (or trigger immediately on power on then never letting go). it's intuitive to look for AC with a scope, then totally forget to look for improper DC offsets...
Thanks, those schematics did help quite a bit
I played with how I trigger a bit after trying to decipher the schematic and was surprised by what I found. If I keep trigger always at +5 and touch velocity/accent line momentarily to +5v and then short, I get a drum hit. It seems like 'trigger' gates the entire drum sound and 'velocity' actually initiates the whole sound/envelopes....
doing this stuff, the drum is close to what it should be.. and I think I've tracked down roughly where my existing mistakes are.
I'm still shocked by the "velocity vs trig" thing. I'd intended to just tie velocity down to a constant voltage and pulse a trigger. I originally intended to modify my 606 to send its trigger out and pull that in as trig in to the 909 kick, now it looks like I'll actually have to pull in both trig and vel/accent.
bizarre since i've never seen any drum machine modified to supply velocity out?? does anyone have insight on this?