11 Jul
2023
11 Jul
'23
10:10 a.m.
For info on DAC internals, have a look at
https://www.analog.com/en/education/education-library/analog-digital-conver…
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(a)classiccmp.org>
Cc: Douglas Taylor <dj.taylor4(a)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, steven(a)malikoff.com steven--- via cctalk wrote:
On
07/10/2023 11:31 PM AEST Mike Katz via cctalk
<cctalk(a)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.