For info on DAC internals, have a look at https://www.analog.com/en/education/education-library/analog-digital-conversion-1986.html Part 2 details basic A/D & D/A architectures
Current output converters are: - less common than voltage output DACs - and, if a ladder conversion architecture is used, lurking inside voltage output DACs behind a transimpedance amplifier (I to V converter) I would be very surprised if the AAV11 does not output buffered volts Lots of other good reference material on analog.com, TI.com is also worth a look Martin PS Most contemporary audio work uses SigmaDelta converters, see e.g. Analog Devices AN-283 and MT-022 -----Original Message----- From: Douglas Taylor via cctalk [mailto:cctalk@classiccmp.org] Sent: 11 July 2023 17:29 To: Mike Katz via cctalk <cctalk@classiccmp.org> Cc: Douglas Taylor <dj.tayl...@comcast.net> Subject: [cctalk] Re: Talking PDP11 The DACs on the AAV11-C board are not marked in any revealing way. I think they are Burr Brown DAC80, 24 pin, but I'm not sure. I wasn't sure if they were working and was looking for a replacement. Looking at the spec sheets DAC's seem to come in Voltage or Current versions. Life got more complicated. This started out as a simple exercise into verifying the AAV11-C operation using PDP11GUI to program up a basic program to run all the codes thru the DAC. It worked, got a ramp out. Now, I'm starting to look at the KWV11-C and how to use that to send values to the DAC at a controllable rate. Doug ------------------ On 7/11/2023 11:41 AM, Mike Katz via cctalk wrote: > 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, ste...@malikoff.com steven--- via cctalk wrote: >>> 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. >
