Some audio amplifier chips can work with single power supply (a positive voltage) or with a split power supply (a positive voltage and a negative voltage). There are pros and cons to both.

A bridge rectifier converts AC voltage to a DC voltage with lots of ups and down, but basically only positive voltage referenced to the minus pin on the rectifier. Capacitors after the bridge rectifier smooth out this DC wave and try to make it as flat as possible.

So the minus on the bridge rectifier is your 0v, your ground.

If you have a transformer with a center tap (the secondary side has three wires, the center wire beeing connected to the center of the secondary winding), or you have a transformer with two separate secondary windings allowing you to connect the two windings in the middle resulting in a three wire secondary, you can use a bridge rectifier to obtain a positive voltage and a negative voltage at the same time. The center tap becomes your 0v , your ground. The minus of the rectifier becomes -v and the positive becomes +v

Have a look at this page, where in the Full Bridge Rectifiers you have on the right side pictures showing you such a circuit, where you get +v and -v using a center tap transformer:

http://www.play-hookey.com/ac_theory/power_supply/ps_rectifiers.html Also, here's some basic formulas.

The peak voltage after it's rectified by a bridge rectifier will be equal to Vac x 1.414 (square root of 2) - 2 x Vdiode , where Vdiode is the voltage drop of one diode in the bridge rectifier. The Vdiode varies depending on what rectifier you buy and how much current flows through the rectifier, and how hot it is... usually it's anything between 0.8v and 1.1v

It's important to keep in mind this peak dc voltage when choosing capacitors, so that you pick a high enough voltage rating. Ex. for 22v AC you have 22 x 1.414 - 2v = 31.1 -2v = ~ 29v .

Imho this is too close for comfort to pick 35v rated capacitors and I'd use 50v rated capacitors.

The capacitance after the bridge rectifier can be determined depending on how low you're willing to let the voltage go. This formula approximates C = Current / [ 2 x Mains Frequency x ( V dc peak - V dc minimum) ]

So for example, going with your 22v AC 400 VA transformer, you have 22v AC and 200VA for each positive and negative voltage, about 200/22 = 9.1A AC so about 0.67 x Iac = 0.67 x 9.1 = 6.A

Assuming you'll have peak DC of 29v and you want to keep your amplifier with at least 24v all the time and you're in US where you have 60 Hz mains frequency then let's figure capacitance up to a safe 6.5A: C = 6.5 / ( 2 x 60 x (29-24)) = 6.5 / 120 x 5 = 6.5 / 600 = 0.01083 Farads or 10840 uF minimum ... so I guess 3 x 4700uF would do, or 4 x 3300 uF, or 5-6 x 2200uF , whatever is convenient.

ps. On the PCBs in your post, the first board it seems instead of one single bridge rectifier (four diodes in a glass passivated package) they're planning to use 4 separate diodes in TO-220 (or similar) packages and have two diodes at a time on a heatsink, probably thinking it would be easier to cool the diodes this way. Still the same thing.

As for the second board, I don't know what the guy that did that was smoking. Seems to me it's some kind of board designed to overcome some limitations regarding height. The board is basically split in the middle, and you have capacitors for the -V on one side, and capacitors for +V on the other side.

It looks like they're making rows of 4 capacitors in series, which results in less capacitance but higher voltage rating. So for example you could put 4 1000uF capacitors rated for 16v and you'd have 250uF and capable of 64v or something like that ( in series, 1/Ctotal = 1/c1 + 1/c2 +... 1/Cn)

But, they screw it all up when they have in the center only 3 capacitors because they had to make room for those holes for V- and V+ on each side sides. Seems silly to me, you could just use a single capacitor rated for higher voltage and mount it horizontally instead of having 4 capacitors of lower height?