operational amplifier circuits call for a split positive and negative 15 volt supply.
The circuit below makes the job of generating such a supply much easier by using an
off-the-shelf DC to DC converter, powered from a cheap 6v battery made from four AA
cells. The converter, part number VESD1-S5-D15-SIP, is available from Digikey,
their catalog number 102-1410, for about $6.00. To insure clean voltages, I follow
the output of the converter with two voltage regulators, also available from Digikey.
The result is a very nice supply rated at 30ma from each supply voltage. This
should be plenty of current for most circuits.