[sdiy] +/- 15v from a wall wart...

[Paul Perry]

You gain a bit, because the peak voltage of the AC cycle is about 1.4 times
the RMS AC voltage.
So, from a 15V AC source, you would get a peak of 21 volts.
Less say a volt for the diode drop & the fact that the mains sine wave is
flattened a bit by all those switch mode power supplies, and you still have
plenty in hand.

This is why I use a 35V rating filter cap after the diode.
A 25V one is likely having its voltage exceeded.

Paul perry Melbourne Australia

-----Original Message-----
>I'm asking for two reasons - one is that I was under the impression that
>voltage regulators like the 78XX series were better served by having an
>input a couple of volts above the output (which is why I was initially
>after an 18 VAC adapter) and two - I'd like to be 'reasonably' sure that if
>someone uses a different - say 15VAC - wall wart, they'll still get
>something approaching +/- 15 Volts.