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“The mains power supply?” I hear you ask.  How on earth is this relevant to hifi? It simply provides the power.  It is a little known fact that your 240V mains is one of the most important factors in getting the best out of your hifi system. You may have heard it said that the most important component of the hifi chain is the source component. After all, garbage in, garbage out! But have you considered that the ‘source’ of power for your entire system is the mains?

Nobody thinks much about the 240V mains power that comes into your home. You flick a switch and the light comes on. You press a button and your kettle boils. Its just there. It powers everything in your home and nobody gives it much thought.
However to those in the know, your mains supply is a double edge sword. It provides the power for your entire hifi system, but it also poses a deadly threat to musical nirvana. Have you ever noticed how involving your hifi system sounds at the end of a late night music session? The reason your system doesn’t normally sound as musically involving and dynamic as it does late at night is because of mains voltage problems.
To understand why, we need to explain a little of how the electricity supply works and how it impacts your hifi system.
The power supply section of your amplifier (for example) takes this oscillating voltage and creates a stable constant voltage level called the supply rail voltage that powers the sensitive circuitry. The power amplifier uses this stable supply voltage to create the output voltage used to drive the loudspeakers. It uses the delicate low level input supplied from the preamplifier or source component and boosts the level with power from the supply rail.

Here is the important part. Any variation in the supply rail voltage finds its way into the final output signal corrupting the musical signal. That is why the power supply section is often the first part of an amplifier that hifi tweakers modify and improve. In all but a select few of the finest components available, the power supply is compromised by design, typically because a product is designed to a price point.

So how does the mains supply affect the supply voltage (and hence the music) and why are we so concerned about mains anyway?
Irregularities in the mains supply from your power company are a part of life. The voltage can be higher than 240V, lower than 240V, there can be irregular sags and dips in the voltage, there can be voltage spikes, fluctuations in frequency, and the list goes on. In fact, all the electricity supply company is obliged to do is provide ‘roughly 240V’. They generally have a tolerance of 10% which means it can vary from below 220V right up to 265V and still be OK from their point of view.

All of these types of irregularities find their way through the power supply section and cause variations in the supply rail voltage. This then affects the delicate audio signal leading to a degradation of musicality. More on that later…

Now, let’s take a look at the different types of mains problems in a little more detail and how to overcome them.

 High or Low Voltage

The Mains voltage at your wall socket should ideally be 240V rms. I won’t go into the details of what “rms” means, other than to say it is a complicated measure of the average AC voltage. The actual voltage delivered can be very different. As previously stated, it can be anywhere from about 220V to 265V and still be considered correct. Moreover it can vary considerably over short periods of time.

To understand why you must consider how electrical power gets to your home. The power station generates very high voltage in the order of hundreds of thousands of volts which is most efficient for transmitting over long distances. High tension power lines – the very high towers running from the power station to the city as shown below carry this voltage. A local substation takes this high tension voltage and drops it down to around 11,000 volts for transmission along city streets. The last stage of the power chain comes with a Stobie pole mounted transformer which takes the 11,000 volts and drops it to the 240V that you use in your home. It is a very long chain with many steps down in voltage. This is part of the reason that it is difficult to maintain an exact 240V level at every house.

The actual voltage delivered to your house has a huge impact on audio components. Consider for a moment how a turntable or CD player works. The motor speed of DC servo units is voltage controlled. A voltage regulated power supply is always employed, but changes in the mains voltage will have a small but perceptible effect on the actual voltage driving the motor. Changes in the speed of playback affects the pitch and rhythm of music and this is quite noticeable. On this basis you would think that a synchronous turntable motor would be better, but there are other more degrading mains related effects that come into play. These will be discussed later. Suffice to say a properly designed DC motor turntable will be better than a synchronous one, all other things being equal.

Variations in Voltage

To complicate matters, the amount of power used affects the voltage. Have you ever noticed how the lights sometimes dim slightly when your fridge turns on? When the compressor in your fridge turns on, it requires a huge amount of current to get started. It can draw tens of amps for a fraction of a second. This causes the mains voltage to drop temporarily resulting is the noticeable dimming of the lights. There are smaller but noticeable changes in the mains voltage every time any equipment in your house (and to a lesser extent in your neighborhood) turns on and off.

So the bottom line is that mains voltage isn’t ever really 240V and it is varying all the time with changes in what is actually being generated by the power station and varying loads in your house and nearby houses.

Variations in Frequency

Variations in mains frequency occur all the time. The Australian power supply is only required to be 50Hz averaged over a day. At times of peak demand, both the voltage and frequency drop. Often, the mains frequency is increased at night in order to ensure that the average daily frequency is the required 50Hz.
Turntables are generally the only audio component generally affected by changes in the mains frequency. This only relates to turntables with synchronous motors. The rotation of synchronous motor is directly locked to the mains frequency. It is synchronous with mains frequency. Therefore if the mains frequency is higher than nominal, the motor runs faster and everything increases in pitch and tends to sound exciting and bright. On the other hand if the frequency is low, the music can sound slow and dull. Worse still is when the mains frequency changes rapidly. In this case, the platter subtly changes speed all the time, possibly introducing audible sonic degradation
DC motor turntables are immune to mains frequency variations and all things being equal, I’d rather have a properly designed DC motor turntable than synchronous motor turntable.

“Noise” on the Mains

More devastating to audio performance than fluctuations in the mains voltage or frequency is mains “noise”. Any variation in the mains voltage other than a pure sine wave is considered noise. Perfectly clean AC mains power is a sine wave voltage as shown below left. A real world AC Mains signal looks more like the figure below right (exaggerated noise level for illustrative purposes). The 240V signal is still there, but there are short term (and sometimes not so short term) transient variations

Clean Mains (Perfect Sine Wave Noisy Mains (Sine wave with noise)