Prototype CD Player

Introduction

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 bass speaker.

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.

Front View

The box was from a dual 5-1/4" hard drive enclosure from way back when 5 MB was usual and 20 MB was huge.

Top view

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 information.

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.

Display

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.