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PSU circuitry basic electronics
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author PSU circuitry basic electronics
jack multiple
I am looking for some more indepth info on how the psu board works. specifically, the two power rails.

i know about the main purpose of it, regulating,rectifing etc for a reliable power supply. its just the rails i dont understand.

Why do some audio projects use/need a +ve an -ve rail. what are the benefits of it.

What exactly is the difference between the 2. an explanation of what this kind of -ve voltage actually is.

yes i'm a beginner, using my project to learn concepts aswell as building a synth.
I don't know if my naïve answer will help, I'm a noob myself.

It seems to me that you can't produce a signal that can vary between positive and begative peeks if you don't feed the circuit with both voltages.

Usually you work with +/-5v (up to +/-10V) outputs so you need at least these.

It's the necessity (sometimes) of 5V that I don't really understand.
jack multiple
have actually found my first reference to this in a book. finally.

not very indepth but a start to answering my questions.

quote ;" most high-fidelity amplifiers use a complimentary design, referred to as a Class AB.

Complimentary amplifiers split the audio waveform into its negative and positive halves and amplify each section separately.
Then they combine the two at the output, rebuilding the waveform.

The technique allows for excellent efficiency because almost no power is dissipated when the waveform is near the zero voltage level.

Only when the input signal gets too big does the amplifier draw a lot of power, keeping power usage proportional to output." end quote.
jack multiple wrote:
Why do some audio projects use/need a +ve an -ve rail. what are the benefits of it.

All voltages are measured with respect to a fixed voltage. In many systems this will be ground or 0V. It's called ground because it is roughly at the same voltage as the ground you are standing on. It is normally connected to earth on your electricity supply but not always.

Audio signals are alternating voltages or currents. If voltages you can think of them moving from positive values to negative values with respect to ground or 0V. This is the simplest way of thinking about it but it isn't always the case. In a split (or dual) rail system such as one used in the Oakley modular, the audio signal can move between the positive supply rail and the negative rail. That is +15V and -15V. Although in reality it won't get much higher than +/-12V.

However, in a single rail system, say one with just a +15V supply, there are normally no negative voltages with respect to ground. Since the audio has to be an alternating voltage or current we must then create a reference point about which the voltage swings. In 9V guitar pedals it is usually half the supply voltage, ie. 4.5V, but it can be anything that will allow the signal to pass through the circuit as the designer intended.

Many designs use a mixture of ground referenced signals and non zero voltage ones. The Journeyman VCF uses ground referenced signals for all the input and outputs, but uses a single rail within the filter core so must create it's own reference for that part of the circuit only.

There are disadvantages and advantages in both systems. It is up to the designer to decide which one will fit in with any particular circuit.

Class AB amplifiers can be made to work on both single rail or split rail supplies. Many older designs used single rail but most newer designs use split rail. The prime disadvantage with using single rail for power amps is that you need to remove the reference voltage, usually half the supply voltage, from the signal before it gets to the loudspeaker. To do this you need a vary large capacitor with a large ripple current rating. Big and expensive.

Split rail power amps can be directly coupled to the loudspeaker, ie. no big cap. However, these are more likely to damage the speaker should a fault occur in one half of the output stage. Therefore protection circuits need to be added.

jack multiple
Thankyou. that's more than helpful.
IF you are asking these questions, I'd stay away from building anything until you get it or at least stay with wall warts. mains power can kill you.
jack multiple
i'm just learning new things . no intentions to play with mains power. thanks for the advice tho.
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