A simple, well-made linear power supply

When looking for a power supply design, it is normal here in 2022 to look for a switching design. They are lightweight, highly effective, and often commercially available at reasonable prices. Their advantages are such that it has become surprisingly rare to see a traditional linear power supply with a line-frequency transformer and rectifier circuit, so [ElectroBoy]The dual voltage power supply board for audio amplifiers is worth a look.

This type of linear power supply has an extremely simple circuit consisting of a transformer, a rectifier bridge and capacitors. The transformer isolates and steps down the AC voltage, the rectifier transforms it to approximate DC, and the capacitors filter the DC to remove as much AC ripple as possible. In an audio power supply, the capacitors have the dual role of filtering and constituting a reservoir of impulses for the power supply in the event of a consumption peak imposed by the music being played. Careful selection is essential, in this case choosing a toroidal mains transformer and good quality capacitors.

The choice between a linear power supply such as this and a switching design for high quality sound is by no means clear cut, and may be something we will consider in our Know Audio series. Desirable properties are the low noise and surge reservoir we mentioned, and it’s probably fair to say that both types of power supply can satisfy them. With the added expense of a toroidal transformer, a linear power supply is unlikely to be the cheaper of the two, but we suspect the balance tips in its favor because a good linear power supply is the easier to design.

Alan A. Seibert