Prototype CD Player
I built this in
1996 as I wanted a known audio source for my amplifiers.
In synopsis I
designed my marble sphere speakers, and was then no longer happy with the
amplification. I designed my amplification and then I was no longer happy with
the source (which was CDs despite their limitations). Along the way I built the
Such is the
slippery slope when one starts off one of those "I wonder if..." thoughts!
The CD player is a
prototype/test vehicle and a "hack" from bits I had to hand, hence the rough and
ready appearance. It does still work and one day "real soon now!" will be
rebuilt into a "proper" box.
The box was from a
dual 5-1/4" hard drive enclosure from way back when 5 MB was usual and 20 MB was
The CD unit is a standard computer CD-ROM drive that
I hacked to access the digital audio serial data and also the time code
The single board computer (big green PCB top right
hand side) was something I had designed for a scientific instrument and used a
Hitachi H8/500 16 bit processor.
The smaller proto-board (small green PCB bottom
left) contains a
NPC SM5842 8x filter chip and differential ECL drivers to the ribbon
cable. I drive the clock and serial data lines separately rather than using a
S/PDIF serializer/de-serializer so I can be sure that there is no added clock jitter as
there isn't any PLL clock recovery.
The Burr Brown 20 bit audio DACs are in the pre-amp
(where they belong) driven from ECL line receivers, so no analog audio
connections are required from a "noisy" digital environment.
Just for the joy of it I ran a 50 foot cable between
the CD player and the DAC/Pre-Amp.
The control panel has a 2 row by 40 character LCD
display with soft menus for function.
The bottom line displays the control options
currently available, whilst the top line displays section and track numbers,
plus the two time codes, one for the current track and the other for the whole
CD (did you know that there were two time codes?).
I made a coarse digital volume control with the
filter, with a mute function, which is displayed on the right hand side. This
involved setting the filter to different input data word lengths which was handy
when playing full amplitude test tones.
I was going to also count soft and hard
(un-correctable) errors but this was not implemented at the time.
All CD player functions can be operated from a
computer over a serial port.