I originally used R-2R DACs but I was lucky enough to be able to buy a
couple of DAC08 chips at Radio Shack and built a circuit using 74LS244
latching buffers so that I could drive both channels of a single 8-bit
parallel port and 2 extra control lines (Select and Strobe).
On 7/11/2023 6:43 AM, [email protected] steven--- via cctalk wrote:
On 07/10/2023 11:31 PM AEST Mike Katz via cctalk <[email protected]> wrote:
Way back in the 80's I was able to do stereo 4 part harmony on a 2 MHZ
6809 using two 8-bit D/A converters.
Much the same here. I recounted this on VCFed a few months ago about building a
simple 2-chip 8-bit ladder DAC with one-transistor amplifier for my Applied
Technology DG680 S100 machine back in the early 80s from this absolutely
excellent BYTE article on how to do polyphonic synthesis on a microcomputer
(KIM-1):
https://archive.org/details/byte-magazine-1977-09/page/n63/mode/2up
A schoolfriend who had an Apple ][ and had not done any Z80 machine code before
asked for me to hand him my Zaks book, upon which he wrote out one attempt in
Z80, crossed it out and wrote a second version. Which worked perfectly. For the
music piece I got it to play four-voice polyphony after painstakingly encoding
Bach's Praeludium in C Major from my mothers' collection of piano music scores.
A few years ago I had thoughts about porting the 6502 code to the PDP-11 and
use the same sort of ladder DAC. Not sure if the slimline 11/05 would be fast
enough for anything too high frequency, but if it was, the slimline 05's power
supply could then temporarily come out and be perhaps be powered off some beefy
batteries in that space, along with a small 1970s transistor amp and 1970s
headphones topped off with a leather shoulder strap to lug it around like a
giant Walkman.
