Allison J Parent <allisonp_at_world.std.com> wrote:
> The problem is the LASER postdates transistors! The optical light source
> would have to be a collminated point source
The objective of the project is not to build a CD player out of only
materials available in the 1940s (although that would be quite a challenge).
It is simply to build a CD player that contains no transistors. Those
silly golden-ears audiophiles think that transistors sound bad, so I'd love
to part them from a few hundred thousand dollars of their money by selling
them a CD player that doesn't contain any of the pesky things.
By this criteria, I could even use a laser diode, and a photodiode as the
detector. But I'm not sure whether the common CD transport mechanisms use
a photodiode or a phototransistor, and I can't use the latter.
Anyhow, using a HeNe laser is preferred because it is a tube.
> Memory is easy, delay lines really big ones!
A delay line isn't particularly suitable for the principle memory requirement
of a CD player. As was pointed out before, early CD players used a 2K*8
SRAM. Newer players use more memory, and in current players that memory
tends to be inside the CD-Audio decoder chip.
But the problem is the purpose of the memory. It serves both as a FIFO to
retime the data to match the crystal-locked timing of the D/A subsystem,
and to de-interleave the data from the disc. The deinterleave process needs
to be able to write the data in an entirely different order than it is read
back, hence a delay line is not usable.
Also, since a delay line generally has a fixed delay (aside from temperature
dependencies and the like), it also can't really be used for the rate
matching.
Core memory definitely seems like the correct approach. A Williams tube
would be neat, but it is too slow, and anyhow they are too hard to find
or fabricate.
Received on Mon Feb 01 1999 - 20:16:06 GMT