Hello. I really don't get a concept of a way to generates negative voltage as a one of the supply voltage to typical OP-AMP. (Operational Amplifier) The output voltages is supposed to swing to more than 10 V thus supply voltages to OP-AMP should be +15V and -15V. I'm thinking of supply these voltages from typical 220 VAC home power line. Could you please give me some ideas? The basic concept of generating negative voltage or simple way of doing this job would be either helpful for me.