[sdiy] 808 Bass Drum

[Tom Arnold]

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.

-- 
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 - Tom Arnold       -  Free Synth DIY webspace http://www.sdiy.org 
 - SynthGeek        -
 - BBD Fanatic      -  "...is it a virus, a drug, or a religion?" 
 - echo evho wjxo   -    Juanita Shrugs. "What's the difference?" 
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