Power Amplifiers

Power amplifiers

What is a power amplifier?

A power amplifier is an electronic device that can increase the power of a signal. It does this by taking energy from a power supply and controlling the output to match the input signal but with a larger amplitude. This in theory just makes the signal overall stronger. It is the amount of power delivered to the load and/or provided by the power supply circuit.

Amplifiers are described according to their input and output properties. they have the property of gain,or multiplication factor that connects the magnitude of the output signal to the input signal.

There are four basic types of amplifiers.

One is the voltage amplifier which is the most common of all. This will change an input voltage to a larger output voltage.

Another is the current amplifier. This amplifier changes an input current to a larger output current.

Another one is the Transconductance amplifier. This amplifier responds to a changing input voltage by delivering a related changing output current.

And another is the, Transresistance amplifier. This amplifier responds to a changing input current by delivering a related changing output voltage. This is also known as a transimpedance amplifier and a current to voltage converter.

QTX QA400 400W Power Amp - this is one out of many power amplifiers. This one is really cheap. It is around £85 and it professional dual channel power amplifiers which gives high quality and dependable performance. It is very simple to use.

This is a picture of the QTX QA400 400W Power Amp.

Power output (watts)

What is a watt?

A watt is how power is measured. It is the unit of power. You can also measure power in joules. This is the units per second. This can be used to express the rate of energy conversion or transfer with respect to time. When an object's velocity is held constant at one meter per second against constant opposing force of one newton the rate at which work is done is 1 watt.

You can also get multiples of watts.

The order is:

Femtowatt- the Femtowatt is equal to one quadrillionth of a watt.

Picowatt - The Picowatt is equal to one trillionth of a watt

Nanowatt - The nanowatt is equal to one billionth (10−9) of a watt. Important powers that are measured in nanowatts are also typically used in reference to radio and radar receivers.

Microwatt - The microwatt is equal to one millionth of a watt

Milliwatt - The Milliwatt is equal to one thousandth of a watt.

Kilowatt - The kilowatt is equal to one thousand watts, or one sthene-metre per second.

Megawatt - The megawatt is equal to one million watts.

Gigawatt - The gigawatt is equal to one billion watts or 1 gigawatt = 1000 megawatts.

And there are many more multiples of watts.

Distortion (THD)

What is distortion?

Googles best definition of the distortion is that Distortion is the alteration of the original shape (or other characteristic) of something, such as an object, image, sound or waveform. However this is something that is normally unwanted sound or buzz some may say. It can be irritating. We try to get rid of it or at least minimize the chances of it. However you may also use distortion as an effect. So although you might not want distortion while recording and it happens without you actually wanting it there. You can also have it placed there. For example you can get a pedal for a guitar that will and the effect of distortion onto anything in which you might play. People use this to add more interesting twist on playing the guitar. Having it connected onto the guitar also means that it will only be on the guitar itself, so you will notice that it is an effect. In conclusion Distortion is when any change made to a waveform. This can also be the case with a simple change in the amplitude, the same occurs to EQ, which is an amplitude change in itself.

You can get many types of distortion. Harmonic, amplitude, Frequency response, phase and group delay distortions. This gives you a wider range of things to do with the ability to distort something and have it as an effect rather than an annoying sound that you simple do not want.

Harmonic distortion is where you layer multiple overtones, making it pleasing to the ears. Total harmonic distortion (THD), as a percentage. This may be expressed in terms of the relative strength of individual components, in decibels, or the root mean square of all harmonic components. However some different types on distortions are more audible than others such as cross over or soft clipping.

Amplitude distortion is distortion occurring in a system, subsystem, or device when the output amplitude is not a linear function of the input amplitude under specified conditions.

Frequency response distortion is a form of distortion that occurs when different frequencies are amplified by different amounts in a filter. However with audio it is mainly caused by the room acoustics itself. Could also be from poor loudspeakers or a microphone.

Phase distortion is a form of distortion mainly occurred from electrical reactance. This is because all of the components of the input signal are not amplified with the same phase shift. This makes some parts of the output signal out of phase with the rest of the output signal.

Group distortion is found only in dispersive media. Phase velocity varies with frequency. In a filter, group delay tends to peak near the cut-off frequency, resulting in pulse distortion.

Sound-to-noise ration

What is Sound-to-noise ratio?

Sound to noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise.it is the ration of signal power to the noise power. This is often known as decibels. If the ratio is higher that 1:1 this could indicate that the there is more signal than noise. This is also the same concept to not only electrical signals, it can also be applied to any form or signal.

The sound to noise ratio is sometimes used informally to refer to the ratio of useful information to false or irrelevant data in a conversation or exchange.

Sensitivity

What is sensitivity?

Sensitivity could be applied to anything musical. It could be how sensitive a drum is on how you hit it. It could also be how hard or gentle you strum a guitar, how you press a key on the keyboard/synth to create a louder or quieter sound. Also sensitivity is also applied to microphones. Different microphones could have different sensitivities than others. They could also just be sensitive to certain range of frequencies. You wouldn’t use the same microphone for vocals as you would for a drum kit. This is because they are tuned for different frequencies. A microphone for a drum is tuned for the lower frequencies. This is the case for a kick drum microphone. And a SM58 is a microphone that is known to be used for live sound vocals. This is because the range that the microphone picks up is within the vocal range of a human.

Sensitivity could also be how sensitive your hearing is. This will also link in with NIHL (noise induced hearing loss). This is where you will partially or fully lose your hearing over time of being exposed to a certain level of frequencies/decibel level which will eventually have an impact on your hearing.

In this case though we are talking about sensitivity in a power amplifier. Well this is measured by the magnitude of input signal need for the amplifier to produce full output, at maximum volume. An example of something that has a sensitivity is a speaker such as a HI-FI. Amplify or amplifier has something to do with the power right? So this will also effect speaker.

By this i mean if something is being played too loud in a speaker that is highly sensitive then you are more likely going to damage it. The diaphragm in the speaker maybe weak/sensitive. This is why we have speakers for different frequencies. We have a subwoofer. This is one that is very good with dealing with low frequencies at a high volume.

Human hears are not very good at picking up quiet low frequencies so we have to turn up the volume of it just so we are able to hear it at the same level as everything else within the mid to high range frequencies.

Getting back to power amps , they , with very high input sensitivity an amplifier will jump up to full volume very quickly as volume is turned up, giving a perception of being powerful, irrespective of true power output. An amplifier with high input sensitivity will also deliver a worse noise figure under measurement, because output noise is in most amplifiers determined by noise from the first stage, multiplied up by subsequent gain.

Connections

Types of power amplifier:

Stand-alone power amplifiers - This is a general type of power amplifier. They amplify the signals sent from mixers to make the speakers produce sound. They can be installed together in racks making it easier to build a larger scale PA system.

Powered mixers – these are mixers with build in power amplifiers. With this, only one powers supply is needed because the mixer and power amplifier and in one. There are also less connections needed to connect a separate power amp and a mixer together, because they areas one. This also gives you more room rather than having multiple pieces of equipment.

Powered speakers – These are speakers with built in power amplifiers. Because the speaker and the power amp is mixed into one, this makes them extremely compatible with each other. This allows the speaker to perform at its best that it can. Giving it its full potential. The mixer output can connect directly to the powered speaker, so there are less cables required. However you can get speakers that are called passive speakers because they need a separate power amp.

The best way to have a small set up and less connection needed PA system, you should get the built in power amp mixer and power amp speaker because this means you have more room to play with, less space being taken up and fewer connections needed. However a stand-alone amplifier allows you more freedom. Freedom with where you place the equipment and expanding the equipment.

Impendence

What does impendence mean?

There are three categories. The output impendence, source impedance and the internal impedance. The output, source and internal impedance of an electronic device is the opposition exhibited by its output terminals to an alternating current of a particular frequency as a result of resistance, inductance and capacitance.

The source resistance of a purely resistive device can be experimentally determined by increasingly loading the device until the voltage across the load is one half of the open circuit voltage. At this point, the load resistance and internal resistance are equal.