[sdiy] +/-12 volts from 9 volt transformer

[Grant Richter]

If you have worked with PAIA stuff you should recognize this.

AC voltage sources are measured in RMS volts - the equivalent DC voltage for
power (heat) calculations.

The peak voltage is 1.414 x 9 RMS = 12.7 volts

Peak to peak voltage is 2.8 x 9 RMS = 25.4 volts

Two half wave rectifiers, one positive and one negative will develop +/-12
volts across the caps as long as there is no load. As load increases, the
ripple will increase.

Using a multiple section RC filter and only a single chip for load, you
should be able to make an acceptable +/-12 volt supply from a 9 AC volt
wallwart and no regulators.

John Simonton has been doing this for years. He just has a tendency to be
overly optimistic about how much load is acceptable.