[sdiy] 808 Bass Drum

[NSSINC]

	It was pretty straight forward when 
I built a few as "modules" to run 
off a paia midi>cv. I eliminated Q39 
and Q40 and ran my trigger pulse 
straight into the circuit from 
there. Try that, if you have more 
problems, I can look more closely at 
what I did. I also put pots in place 
of r165 and r166 to control the 
initial and final freq.

-Al



Tom Arnold wrote:
> Is it just me or the the 808 Bass drum a really finicky circuit?
> 
> I have it cooked up on a board using the MicroLarge layout.  After reading
> the 808 service manual a bit I removed Q39 and connected R154 directly to
> ground.  My reasoning for this is the BD signal is the Drum Select and not 
> actually the trigger, the trigger pulse is shot at it on the "accent" line 
> through Q40.  I put a small cap in series with the input and a 10k
> resistor to ground from the input side of the cap so that I could just pulse
> the circuit for testing  the cap/resistor give me roughly a 1ms wide pulse
> although not very clean.  Anyhow, that proved that the circuit worked.  The
> narrower I made that input pulse, the cleaner the drum got.   I figured the
> next best step was to really clean up the input so I build a quick one shot
> using a 4013 and now I have a very clean 1ms wide pulse, but a nasty pop at
> the hit of the drum.  The exact opposite direction from my expected/intended
> result.
> 
> And to think, I assumed I'd just need to clean up the trigger and add a
> buffer on the output ( with a delay-on anti-thump ) and have something to
> turn into a module.
>