MC34063 dc/dc, LM358 or such opamp and a simple push-pull output using
2N3904+2N3906 driven by the opamp. The push-pull stage inverts so the opamp must
be connected to account for this. Designing the protection circuits so the
interface is not destroyed by spikes from the car electrical system or from the
frame/ground/building will be harder than the amplifier proper imho.

Peter


-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist