via this auction
D/A in 77. Anyone know what these were specifically used with?
Sunday, September 30, 2007
4 comments:
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It appears that it could be used with any computer with an 8-bit parallel port for sequencing, etc. Probably used with any one of the first microcomputers? Looks like the low 6 bits specify the control voltage (64 possible levels) and the highest two can be used to output gate signals etc.
ReplyDeleteThis module was a D/A converter, albeit a specialized one for PAiA and/or any other synth that used a Hz/V control voltage scheme (not Octave/V). The interface on the back of the card is an 8 bit data bus and a strobe. The card had a 6 bit D/A converter and the "flags" could be used as triggers or to control a QuASH.
ReplyDeleteIn a PAiA system, the 8780 would be paired with an 8700 computer and one or more 8781 QuASH modules. The 8700 computer was 6503 based and provided a basic polyphonic keyboard scanner and channel assignment(as well as some other things like an arpeggiator, or any other code the user wanted to write - open source!, there was a cassette interface for program storage).
The 8781 QuASH was a Quad Analog Sample and Hold. The computer would write a digital value to the D/A and then latch the analog output in one of the 4 channels of the QuASH. Providing upto 4 channels of control voltage output.
If MIDI had been known at the time this was invented, then the 8700 would have had a MIDI interface, and the combination of all the 87xx modules would have provided a basic 4 channel MIDI->CV converter. The D/A and QuASH is a precursor to the PAiA MIDI2CV8
I believe it was possible to have multiple QuASH modules thereby allowing more than 4 voice polyphony. Here's a link to a complete PAiA system with 87xx modules:
http://www.synrise.de/thumbs/t_p4700j.jpg
Kind of reminds me of the MMM...
Here's a link to an auction of an 8700 and QuASH:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=160160571111
It was pretty cool DIY stuff for 1977. I ended up cloning John's design for a college project, replacing the 8700 computer with a DEC PDP-11/20 and the other 87xx modules with a bunch of hand wired perfboard. But that's another story. For reference here are a couple of pics of an 11/20:
http://www.piercefuller.com/library/img10083.html?id=img10083
http://www.piercefuller.com/library/img10084.html?id=img10084
A close up of the console:
http://webpages.charter.net/thecomputercollection/pdp11/pdp1120a.jpg
Ah the good old days of pre-PC computing...
Details about the whole PAiA computer control including the DAC and QuASH can be found in John Simonton's "Friendly Stories About Computers/Synthesizers". It is an interesting read if you like ancient synth history and a good tutorial about how a computer can scan a keyboard and generate multiple CVs. I have a scan by Anders Spoton that no longer seems to exist on the web. I'm not sure where I grabbed it from.
ReplyDeletei have on and i love it :)
ReplyDelete