Electrical Theory

Electrical theory

Ground loops

All audio cables contain a screen connection which Is earthed They all have electronic resistance. As a result when a current is passed a voltage will be produced at the two points.

As the power cables and cheer connections all interconnect any Interference can cause a current to flow in the ground connection often causing an audible distortion or noise Often a 50htz hum will be heard as the loops act like a transformer.

Elimination

They are eliminated by only having one other to ground for each audio component This is achieved by removing either the audio screen at one end of the cable or removing the earth cable from the power supply this is highly dangerous do not do it!! Removing the screen from an unbalanced cable can result in radio interference. This will, In theory, make it into an antenna.

Removing the screen from a balanced cable will not pose an issue as it does not act as a return path for the audio Removing the ground loop from a power supply and u balanced screen can also remove the return path for audio and a loud hum in your monitoring system Adding a 100ohn register to a jack cable can reduce the hum but can also make the system more susceptible to RF interference Of the equipment had got a ground lady function use it.

This disconnects the usage of the ground cable. Used balanced cables when possible.

WATTS, VOLTAGE, CURRENT, AND RESISTANCE

Voltage is measured in volts Currents (I) is measured in amps and resistance is measured in ohms. Analogy of what these mean. The voltage is equivalent to the water pressure, the current is equivalent to the flow rate and the resistance is the pipe size.

This is a better way to understand how these work. Current is equal to the voltage divided by resistance Electrical power is measured in watts In an electrical system power (p) is equal to the voltage multiplied by the current. RMS on a speaker would I dictate the speakers maximum continuous handling capability All audio signals could be said to have a maximum and a minimum RMS value.

It is a useful function to understanding when discussing signal levels and power levels of speakers ,especially when trying to match equipment You should use an amplifier rated as twice the RMS. As the speakers but the same impedance.

If you have a voltage too high running through a cable that cannot handle that level of voltage, you may have a fire and the cable could melt. This is because the current is too high sand it will get too hot and break, burn up, melt, or even catch fire. And you want to make sure you know as much as you can about the safety of dealing with cable and the level of watts it can handle.

To solve this you use a speak on cable. This is because it is safer because of the level it can handle without it being dangerous.

An amplifier should be twice the power of the speaker.

for example a 250 watt speakers needs 500 watt amp RMS. But you could also have it higher that that. Just needs to be in the range of 0.8 or 1.25 ( 400 - 625) . This means everything is going to run efficiently.

AMP If the amp is not powerful enough then the speaker will cut out and overheat. If the amp is too powerful, then you could blow the speaker. Either way you could damage your amplifier or your speaker in one way or another.

Calculating the power requirements.

Most audio equipment isn’t 100% efficient, a lot of the power consumed is converted in heat – consider how hot your speakers or amplifiers become when powered up.

As a result a useful figure (when you don’t have the manufacturers stated figure) to use 1, 4 by multiplying the wattage by this you are likely to get a more realistic wattage figure for the equipment.

Gain staging.

Ideal gain staging occurs when each component in an audio signal flow is receiving and transmitting signal in the optimum region of its dynamic range.

EARTHING

What is earthing?

Earthing is the reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the Earth.

Protection devices

Circuit breakers

This keeps you safer if something goes wrong in the whole circuit of electricity. Much like an electric box in a house if a fuse goes or there is a fault with an appliance then the switch will go off in the box to indicate what part of the house or what appliance has tripped the switch. This keeps you safe when handling electricity. Same goes with if an electrician has been fiddling with the electrics and he’s about to be electrocuted then the trip switch kicks in and stops him from getting shocked.

PAT testing. (Portable appliance testing)