Well, we're done!
Mainboard again. Analogue O/P stage replaced with LME49720 op amp, a studio grade audio specific device. Decoupling caps replaced, output DC blocking caps replaced with Silmic (again, and audio grade type) of higher value (100uF instead of 47uF to extend LF further). Wurth Elektronik RF absorber added to CPU, DAC and decoder (DAC and decoder under the board). Clock crystal can grounded, bonded and damped with rubber grommet (crystals are very microphonic - this is a seriously good idea on ANY cd player!). External low noise regulated supply built for LME49720.
Everything back together again, new supply on veroboard on right, with it's own independent transformer as the one in there doesn't supply sufficient headroom for regulated +/-17v rails. I went for +/-17v as the LME allows it, and a higher voltage swing = better signal headroom / lower distortion.
Soak testing, spinning The Pixies 'Surfer Rosa'
Sounds pretty damned excellent, noticed a smooth almost 'analogue' style of presentation and some seriously good 'attack' and transient ability. Drums on 'Where is my mind' are in the room!
Just for laughs, this the distortion plot for the LME on a 17v supply. As you can see, at standard CD output voltage level of 2V, the distortion figure is 0.00004%, which is to all intents and purposes, un-measurable, so the analogue stage in this player isn't contributing to the overall distortion performance, which is now down to the DAC. Nice...
"Two very small men cutting steps in the roof of the world"