[sdiy] 3/4 bit A/D converter (was: Sample&Hold thoughts)

Happy Harry paia2720 at hotmail.com
Wed Mar 14 15:44:27 CET 2001

Sure, I'd like to see it. Seems like another possible
use for the LM3914 bar graph display chip also.

H^) harry

>From: Michael Buchstaller <buchi at takeonetech.de>
>Reply-To: buchi at takeonetech.de
>To: synth-diy at node12b53.a2000.nl
>Subject: [sdiy] 3/4 bit A/D converter (was: Sample&Hold thoughts)
>Date: Wed, 14 Mar 2001 11:04:58 +0100
> >I'd use a good parallel A/D converter (12-16 bit), clocked at maybe a 
> >44khz rate... then feed it to a D/A converter (12-16 bit) but
> >add switches to selectively disable bits starting with the LSB...
> >
> >so its 12bit, 11bit, 10bit, .... 4bit ?
>I have done a module that consists of a string of 17 equal resistors, 
>16 voltage levels. Those are fed into the "-" input of 16 comparators, the
>"+" inputs are all together connected to the input signal.
>All comparator outputs are summed with equal resistors.
>That gives effectively a 4-bit A-->D and then back D-->A conversion. I have
>made the top end and the bottom end of the resistor string CV controllable.
>*very* interesting effects when you put LFO´s in there !
>This makes very strange sounds; depending on which signals you feed
>into it. When putting CV´s through it, it behaves lika sort of a quantizer.
>The 3-bit version does use only 9 resistors(8 levels); here the effect is 
>more pronounced.
>You can make very simlpe saws and drum sounds sound *very* electronical
>and strange - highly recommended !
>If anybody is really interested, i could put up the schemo on my web site.
>I have been using LM324 as comparators, so it is a cheap 4-IC solution.
>(OK, 5 IC when i use 2 of the additional Opamps as unitiy gain followers to
>drive the resistor string, and one more as an output amp)
>-Michael Buchstaller

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