Symmetrical supply in cars
There is a problem if you want to use a car battery to power a circuit which requires a symmetrical supply voltage. Having abandoned the idea of mounting a second battery in your car for that purpose, take a serious look at the circuit discussed here. It converts the car battery voltage into symmetrical ±12 V or even ±15 V rails. Since the converter is able to supply a continuous output current of about 0.5 A, and a peak current of up to 1 A, it is eminently suited to powering control amplifiers and small power amplifiers.