Requires Eagle by CadSoft
DOWNLOAD CY-668A SCHEMATIC
A few people have remarked on a sort of tinkling noise which accompanies bass sounds with the CY-668A.
It's a sort of nasty whine which accompanies bass sounds with a tinkling quality. One culprit would be the stereo pilot and multiplex, although more likely would be reference frequency breakthrough. The PLL chip specs and the fact that a 10.24MHz reference crystal is used point towards the conclusion that the phase detector frequency can be no higher than 10kHz, and may well be lower. At peaks of bass deviation the loop is 'fighting' the modulation and this is when the audible breakthrough will occur.
As yet incomplete and in places erroneous schematic from what I've pieced together.
Requires Eagle by CadSoft
DOWNLOAD CY-668A SCHEMATIC