Andy, (and others that may be able to help) I notice you seem pretty clued up on electronics. capacitors etc and especially the 555 timer chip. I've put together a PWM controller kit that drive the engines fine. However a reason why I did this is to get a few more electonic facilities for the engines (before moving to DCC) which I understands works using PWM at the individual engine level, rather than the layout itself. Problem: I also put together a kit that generates realistic deisel sound and the module sits inside the engine. It uses the back EMF voltage generated by the motor to determine the sound level (ie idle, revving etc) The circuit looks for the back EMF feeback AC voltage generated by the motor, in between the DC pulses generated by the PWM controller. However, I cannot seem to get it to work. The sound is fine however does not alter when the PWM controller is varied. It does not make any difference whether the engine is on the track or not. I believe there may be a problem with the controller as there is a diode that filters the back EMF out so as not to damage the controller. Could this also effect the sound generator so it would not pick up the back EMF? Mulit meter testing does detect back EMF AC voltage across the tracks. I can post the circuit diagrams if that would assist, but not sure how to include them in a post. Any ideas? Thanks, TOOT!