24 Aug
2004
24 Aug
'04
4:23 p.m.
Years ago, I owned a data cassette drive made by a
company called National Multiplex, presumably long
defunct. It was obviously a modified audio cassette
recorder, but in which the internal electronics had
been completely replaced. Unlike the prevailing
standard for cassette-based data storage on micros
in that day, this drive used saturation recording
(NRZI, I believe) instead of a modulated audio carrier.
It was a very functional replacement for a paper tape
reader/punch, and ran up to 9600 bps using hi-fi grade
audio tapes.
I would be interested in locating one of these beasts
to replicate the setup I had on my IMSAI before I sold
the drive years ago. The drive came with schematics,
and as far as I remember, the circuitry was rather
simple -- a couple of op amps and a few gates.
Alternately, if I can locate a copy of the drawings,
I may attempt to reproduce the design using a
contemporary audio cassette mechanism.
Has anyone ever seen one of these?
--Bill
Yes, I still have the one I used with my SWTPC 6800,
along with the supplied documentation. The unit is
just a modified portable cassette player. National
Multiplex gutted the usual cassette player-recorder
circuitry and installed their circuit board. They also
increased the tape drive speed (by changing the diameter
of the drive motor pulley, IIRC). There were several
models, but they were all called Computer Aid. The square
black plastic model CCA-7 was the most popular and are
the ones I have. This model has the level meter on it.
I found and purchased another on eBay several years
ago, so they're still out there. Another model is the
rectangular silver Computer Aid model DC-3. If I come
across my documentation for it (I have a good idea where
it is, I just don't have the time to look for it), I'll
scan it and send you the url. It'll be on swtpc.com
somewhere.
Bill