Earlier, in the article How to Change Alternating Current into Direct Current and Supply DC Electronic Circuitry With Power, I wrote about supplying power to electronic equipment by transforming AC household mains electricity into a low voltage stabilised DC supply with which to run the circuitry incorporated in the device. In that article I mentioned the transformer – which transforms the high-voltage AC into low-voltage AC current, the rectifier – which changes AC electricity into a crude type of DC current, and the smoothing capacitors/inductors plus the voltage regulator chips – which stabilise and regulate the waveform before the final product is outputted to the electronic circuitry which it powers.

What I touched upon there was a single-supply, with a negative and a positive output: Straight DC, no frills. Sometimes; however, more than one supply of power is needed in order to power more than a single circuit, and/or to maintain separation between two parts of a single circuit; such as in a stereo amplifier, for instance: if both channels were supplied by exactly the same power feed then there would be a loss of separation and significant bleedover between the two channels. To avoid this a dual balanced supply is used.

A dual balanced supply is, basically, a mirrored supply: Think of the zero-volt or ground line as the mirror. Since the mirror is reflecting +V and 0V, then the reflection is the negative of that; supplying 0V and –V. To make this a little clearer, let’s say that +V = +12V and –V = –12V: Across the extremities, then, from +12V to –12V, exists a potential difference of 24 volts. – Across +12V and 0V exists a potential difference of only 12V, as well as across 0V and –12V. There are in effect two 12 volt supplies OR a single 24-volt supply; depending upon whichever way you choose to look at it.

The simplest type of dual balanced supply can be made from two batteries connected in series. The 0V tap is run from the join between the two batteries: -

Each battery supplies six volts; therefore the potential across +6V and –6V will be 12V. Between +6V and 0v, as well as, separately, between 0V and –6V, the potential will be only 6V respectively.

Moving on to bigger things; a dual balanced supply (Below) can be extracted from normal household mains electricity too. – Using the principles I mentioned in the other article, but mirrored, like I was saying above: -

Notice the two regulated supplies are series-connected, just as with the batteries.

In the diagram below you’ll see an example of how a dual balanced supply powers a stereo amplifier; maintaining channel separation, which I talked about above.

Well I’ve not gone into gargantuan detail by any means: Nevertheless I hope that this article makes the issue a little clearer as to what a dual balanced supply is, as well as its usage.