I've answered a couple of questions recently about power supplies for low-power amplifiers such as cmoys.
It's better to use a supply with a true ground rather than the virtual grounds that are used with many amps which run off a single battery or DC wall wart.
I like to use a supply based on 2 unregulated DC wallwarts, such as the arrangement shown here.
This has the least problems with RF interference and the smallest number of components on the board, but it does have some problems, such as the fact that if one wallwart is left unconnected the lopsided supply can cause damage to headphones. I have a solution to this that I use, but it complicates the circuit and adds to the expense.
It is possible to use a supply based on a single AC wallwart. Here is an example circuit:
The above circuit is adjustable, and requires to be set up to give the correct output on both rails by tweaking the trimpots RV1 and RV2. Use a Bourns or other good quality 20- or 25-turn trimmer in this position. It will work with a variety of AC wallwarts from 5vac to 24vac. If a high input voltage and low output voltage are chosen, however, the regulators may run hot (require heatsinks) particularly if the current drawn is high.
An simpler alternative is to use fixed regulators as here:
78xx and 79xx series regulators are available in voltages from 5V to 24V, and you can substitute any voltage you require. A simple rule of thumb is to use an AC adapter with an AC voltage equal to the DC output required, this should provide a voltage to the regulators sufficient to exceed the dropout, except perhaps in the case of +/- 5V output supplies, in this case an AC wallwart of 6vac or 9vac should be used.
One issue with this arrangement is that the current drawn from the adapter has quite pronounced spikes, so to minimise any RF radiation which may be picked up and become audible on the amplifier output it may be desirable to wind a few turns of the lead from the wallwart through a ferrite suppressor close to the torpedo plug where it connects to the circuit. This will reduce the RF getting onto the cable which will act as a transmit antenna.
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