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

[Michael Buchstaller]

>I'd use a good parallel A/D converter (12-16 bit), clocked at maybe a fixed 
>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, giving
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 even
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