power amps

[chappy]

im just writing my speech for my drama exam for the technical course I am taking, and I have to write about what everything I use does. now I no what the power amp does, but I'm just having trouble explaining exactly what it does in technical terms. for example I would write ...' the power amp is a vital part of any p.a. set up, it takes the signal from the mixing desk and...(need help with this bit here)...so that high powered speakers can be used.'

 

any help would be much appreciated

[Ben Langfeld]

Amplifies the signal.... Pretty much that simple.

[chappy]

Amplifies the signal.... Pretty much that simple.

 

 

I... errr...kinda feel a lil stupid now :P wasnt sure if there was maybe a more technical explanation

 

 

cheers

[Rob_Beech]

Chappy

 

have a wander over to http://www.blue-room.org.uk/wiki/Amplifiers to start with.

 

Section 12 of the yamaha sound reinforcement handbook aptly named Power Amplifiers will go into much more detail.

 

There are also many other books on the matter. its also safe to say if the Wiki doesn't describe it as you want it. google may well be your friend.

[lightsource]

im just writing my speech for my drama exam for the technical course I am taking

 

any help would be much appreciated

 

 

I hope your spelling and punctuation are just a little bit better than what has appeared in this post.

 

Remember:

 

mW = Milliwatts

MW = Megawatts

 

Big difference, punctuation is VERY important. Don't be lazy <_<

[paulears]

I always remember my physics teacher telling me that the ideal amplifier would be a piece of wire with gain. Replication of the input at the output with nothing added apart from amplitude.

[d_korman]

I always remember my physics teacher telling me that the ideal amplifier would be a piece of wire with gain. Replication of the input at the output with nothing added apart from amplitude.

 

which is an over-simplfication, as what you need is CURRENT gain, not voltage gain. Depending on the load impedance, you may not actually get any increase in the signal amplitude at all - what you get is the ability to drive a current through the load that is proportional to the incoming signal voltage.

[Rob_Beech]

which is an over-simplfication,

what you get is the ability to drive a current through the load that is proportional to the incoming signal voltage.

 

So which do you want?

[mackerr]

which is an over-simplfication, as what you need is CURRENT gain, not voltage gain. Depending on the load impedance, you may not actually get any increase in the signal amplitude at all - what you get is the ability to drive a current through the load that is proportional to the incoming signal voltage.

Modern audio power amplifiers are Voltage Amplifiers. There will be limits to their power capability that are current based, hence the limitation on how low the load impedance can be, as well as voltage based due to the rail voltage being as far as you an go, but what is being amplified is voltage.

 

Mac

[paulears]

Interesting this one - I don't think a volt or so of audio is much use, is it? Thanks Mac

[JimWebber]

which is an over-simplfication, as what you need is CURRENT gain, not voltage gain. Depending on the load impedance, you may not actually get any increase in the signal amplitude at all - what you get is the ability to drive a current through the load that is proportional to the incoming signal voltage.

 

Yes, but surely current is a result of voltage?

 

I agree, it is current flowing through the speaker coil, that makes it move. The higher the current, the higher the magnetic flux, and the further it moves.

 

However current is not something that just happens, it is a result of voltage and resistance, or in this case impedance. - Simple Ohms law. (Although to be pedantic Ohms law is actuallly R = V/I)

 

I seem to remember, that in an amplifier, there is a resistor in line with the transistor, such that the current gain of the transistor will cause a voltage drop across the resistor. this voltage is then fed to the output. (This was *cough* years ago now, so I may be off on this one!!)

 

The "Straight wire with gain" maxim is a good one though!

 

Jim

[Simon Lewis]

Loudspeakers present amplifiers with a complex load. Since most loudspeakers do not compensate for changes in the impedance / frequency curve, then we must ensure that there are minimal changes in the amplifier signal voltage irrespective of the current drawn.

 

To achieve this, the amplifier must be capable of delivering a high current. This typically means a low amplifier output impedance. Furthermore, the fact that loudspeakers produce a back EMF means that that a low amplifier output impedance is needed to provide the necessary damping.

 

Therefore, modern amplifiers are typically voltage sources with sufficient current sourcing and current sinking capability to drive the loudspeaker load.