> On 07/10/2023 11:31 PM AEST Mike Katz via cctalk <cctalk@classiccmp.org> > 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.
