Whats that weird motor noise I get with my portable CD player?
Many people report problems while playing CDs from a portable CD player into their car audio systems. The problem, stated very simply, has to do with the stepping of the motor requiring a varying amount of current and non-isolated power and audio signal grounds. Using a liberal application of capacitors and inductors, this voltage variance can be restricted to a window of 8.990 to 9.005V for a 9V CD player, yet even the swing between these two levels is enough to cause annoyingly loud noise on the outputs. It has been reported that this entire problem can be solved by using a true DC-DC inverter at the power input to the CD player.
