[sdiy] Back to that drum topic...

[Happy Harry]

Hi Gene....

inline


>From: Gene Stopp <gene at ixiacom.com>
>To: synth-diy at dropmix.xs4all.nl
>Subject: [sdiy] Back to that drum topic...
>Date: Wed, 3 Apr 2002 12:59:29 -0800
>
>Hi DIY,
>
>Been watching that drum thread recently... turns out I've been tossing
>around the same kind of ideas lately. A while back I made a drum set for my
>kids (which is a great excuse these days to make something for ME). It
>consists of an Alesis DM-5 rackmount drum module and a bunch of old
>margarine tubs with PC speakers in them as triggers. The tubs are screwed
>into a piece of wood mounted on top of the DM-5 so the whole thing is
>somewhat portable. It was meant as a test setup but it worked so good that
>it's still that way.
>
>Anyway I also have a Moog drum controller that sits next to it, going into
>my big analog mess in the music room. It's currently wired into a modular
>and naturally makes some pretty wild sounds. I want to free up the modular
>stuff and make a little portable sound module dedicated to the drum -
>something portable that makes noise and holds a power supply for the drum.
>
>So here's what I've been thinking:
>
>a) An ASM-1 stuffed with low-cost parts like non-matched pairs and no
>tempco's (save those parts for keyboard use), with some kind of limited
>front panel controls pre-patched for drum noises
>
>or
>
>b) Some kind of circuit dedicated to percussive synthesis
>
>One idea:
>
>Multiple fixed oscillators at non-harmonic intervals each with their own
>decay envelope
>
>Osc 1 ---> VCA ---> output mixer
>Env 1 ------^
>
>This circuit times six or eight? Each osc would have a tune control, each
>env would have a decay control. Also one chain with a noise source instead
>of an oscillator maybe...
>
>I'm thinking the oscillators could be simple tri-square dual op-amp jobbies
>with a tune pot. The VCA's could be 3080's etc. (you can mix their outputs
>by shorting them together, I've been told)

That is correct. They are current sources. You can use a single
resistor to ground or drive into an inverting summer directly
(no input resistors... just feedback)

. The Env's could be simple
>decay-only contours all hit with the same trigger pulse.
>
>Any thoughts? Would it be useful to apply the envelopes to the pitch of the
>oscillators, also? Is there a cheap low-parts-count way to slightly alter
>the frequency of the integrator-comparator type of oscillator without 
>making
>the integrator an OTA?

Yes... there is a VCO that uses an integrator with the CV signal
fed to both opamp inputs... with a transistor to shory one to
ground to change the polarity. The Roland TR-909 uses this approach.

H^) harry
>
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>
>
>Best Regards,
>
>- Gene
>




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