How much power do amplifiers draw?

[rob1963]

I will soon be buying a new amplifier which puts out 500 watts RMS per channel (at 8 ohms).

Therefore I'll have a 1kW system (if running it at the maximum).

My question is this: How much power will the amplifier draw from the mains?

I'm assuming it will actually be MORE than 1kW, to allow for ineffeciencies, but how much more?

:confused:

[BeerFunk]

As I understand it, a good amp will have an efficiency 'plug to plug' of around 80-85%. Turning that around, 1/0.8 = 1.25, so based on that, I reckon around 1250W. I could, of course, be wrong, but I am fairly sure.

Why do you ask, Rob? :confused:

[Thames Valley Discos]

My QSC RMX 2450 takes about 2 amp running without clipping. If run fully clipping this can go to 8 amps. So anything from 480W to 1.9KW Hope this helps. Or try buying one of these to get accurate reading http://www.maplin.co.uk/Module.aspx?ModuleNo=38343&C=Newsletter&U=07P08-2&T=12078696

[Tony Scott]

As I understand it, a good amp will have an efficiency 'plug to plug' of around 80-85%. Turning that around, 1/0.8 = 1.25, so based on that, I reckon around 1250W. I could, of course, be wrong, but I am fairly sure.

Agreed, allow about 5amps used at max without clipping.


Why do you ask, Rob? :confused:

Could it be Rob is worried about running everything off of one lead?! :D :D

See here: http://www.mobilediscodirectory.co.uk/forums/showthread.php?t=7653&highlight=power

[rob1963]

Why do you ask, Rob? :confused:


Could it be Rob is worried about running everything off of one lead?! :D :D
See here: http://www.mobilediscodirectory.co.uk/forums/showthread.php?t=7653&highlight=power

Exactly, Tony!

As I recently stated, I currently run everything off one wall socket.

However, the new amp I'm getting is nearly 500 watts more that my current one, which will take my total power requirements for the large disco to MORE than the 3 kW which one socket supplies.

I'll therefore need to start using 2 sockets for my large disco: one for the amp & another for everything else.

:)

[CRAZY K]

I will soon be buying a new amplifier which puts out 500 watts RMS per channel (at 8 ohms).

Therefore I'll have a 1kW system (if running it at the maximum).

My question is this: How much power will the amplifier draw from the mains?

I'm assuming it will actually be MORE than 1kW, to allow for ineffeciencies, but how much more?

:confused:

Rob, this all sounds OTT to me:eek:

My Peavey 1000watt Mixer Amp has a nominal power need of 500watts according to the manual--- Peavey themselves say it could be 600 watts and double it for a generator.

So with my calculator thats 600 divided by 240= b all!

If possible I tend to run with two separate mains if using Lights but unless you have a massive Lightshow and a BIG Sound System I doubt if you would need to change anything---just my opinion no liability accepted etc.

I have used my full set up---not as big as most--on a cable I use which is PAT tested and in thickness terms no more than 2mm.probably less.

Thats Peavey sound, various mixers, 2 Mini Discs, CD player, Radio Mike,
2 Dynatwins, 4 Big Par Lamps, and 2 Moonflower effects. Oh and Cortex.

If your worried consider using Arctic cable 2.5mm which is rated 16 amps or maybe more. £1 a metre roughly. I have one for Marquee work.

Thats what my DJ shop recommended.

Obviously you cant run more than 13 amps but its good heavy duty stuff, hard wearing and I guess would prevent any overheating:D

I assume you dont use a thin Bedroom DJ £3 Woolworths mains lead:D :D :D

Perhaps you local DJ shop could offer advice---if you use one:)

regards

CRAZY K

[rob1963]

My Peavey 1000 watt Mixer Amp has a nominal power need of 500 watts according to the manual CRAZY K

Sorry Crazy, but you've lost me there.

How can a mixer amp which only draws 500 watts from the mains put out 1000 watts of power?

Where does the other 500 watts it puts out come from?

I know I'm missing something here...I just don't know what!

:confused:

[Danno13]

I find its always a good idea to use a sperate socket for the amps - it stops that click you sometimes get if you use a smoke machine.

[TonyB]

Sorry Crazy, but you've lost me there.

How can a mixer amp which only draws 500 watts from the mains put out 1000 watts of power?

Where does the other 500 watts it puts out come from?

I know I'm missing something here...I just don't know what!

:confused:

Because an amp doesn't run at full range and full gain all the time. Because of the variation in the sound wave supplied to the amp, the average power used is less than the peak watts that the amp can produce. Amps have a capacitor that stores current that copes with most peaks without having to draw any extra current from the mains supply.

I don't feel like I am explaining this very well! but an amp doesn't run at full power all the time. You would have to have a full range constant signal at maximum gain for that to happen but music has high and lows that average out so it doesn't happen.

An amp usually draws less power from the mains than it rated power handling.

[rob1963]

Because an amp doesn't run at full range and full gain all the time. Because of the variation in the sound wave supplied to the amp, the average power used is less than the peak watts that the amp can produce. Amps have a capacitor that stores current that copes with most peaks without having to draw any extra current from the mains supply.

I don't feel like I am explaining this very well! but an amp doesn't run at full power all the time. You would have to have a full range constant signal at maximum gain for that to happen but music has high and lows that average out so it doesn't happen.

An amp usually draws less power from the mains than it rated power handling.

Ok, now I'm totally confused!

I always thought amps drew MORE from the mains than they put out (to allow for inefficiencies).

Beerfunk confirmed that by stating that they draw about 25% more than they put out...

...now Crazy & you have suggested they draw LESS that they put out!

:confused: :confused: :confused:

[CRAZY K]

Sorry Crazy, but you've lost me there.

How can a mixer amp which only draws 500 watts from the mains put out 1000 watts of power?

Where does the other 500 watts it puts out come from?

I know I'm missing something here...I just don't know what!

:confused:

A basic understanding of electronics!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Power in your mains cable AMPS AND VOLTS has absolutely nothing to do with watts of music output--other than a bigger amp needs more current --i.e.amps to drive more watts of ELECTRIC power in the amp to produce watts of MUSIC power.

I wont go on anymore--I dont think you are going to have a problem--no liability accepted for this advice--

regards

CRAZY K

[Jiggles]

Rob stop messing with the laws of Physics!!!:D:D:D:D:D:D

[Dragonfly]

Rob stop messing with the laws of Physics!!!:D:D:D:D:D:D

Thats Callums job!!!!! and his answer to the original question......

"enough to start a small yet significant house fire" :D :D :D :D

[Thames Valley Discos]

Q: Is there an ‘industry standard’ for the input sensitivity level of professional power amplifiers?
• A: The answer to this question is regrettably ‘NO’. There are two different schools of thought -- design
with a constant input sensitivity, or design with a constant gain. This makes it difficult to substitute
amplifiers within a system – the user must first understand the amplifier’s gain structure.
When different amplifiers are used within a system, there should be negligible auditory differences
(aside from overall loudness, of course). However, mismatches can occur when an amp with a different
gain structure is introduced into a system. This could result in the notion that replacement is “not as
loud” or “distorts too easily”, when, in reality, the variation is due to different manufacturer having
different policies about input sensitivity.
The first school of thought sets the input sensitivity (signal level required for full output) of all models
to the same value, regardless of power. This policy is used on the RMX, ISA, CX, PL2, and
PowerLight series. The results of this policy are:
1. The relative "loudness" of two different amps will track their power ratings. A more powerful amp
will sound louder than a smaller model, but all the amps will clip at the same input level.
2. The gain will be different for each power point. (This is a direct consequence of holding the input
sensitivity constant.)
3. The input headroom will always be the same for fixed level sources. This makes it easy to connect
different power amplifiers to a given line level, but by the same token, a larger amp will sound
louder and amplify any noise floor by a greater degree.
4. Even within the “constant sensitivity” realm there are differences. Popular sensitivity levels
include: 0.775 (0dBm), 1.0V (0dBv), and 1.23V (+4dBm). As powers have increased, QSC has
settled on an input close to 1.23V (+4dBm) to reduce the noise floor.
The constant gain concept (as used in QSC’s PLX amplifiers) keeps the gain (the degree of
amplification) the same for differing power levels within a series. This has the following results:
1. Amps of different powers sound "equally loud" -- buying extra power results in extra headroom,
not more volume. Therefore, a larger amp will "clip later" than a smaller amp, but operators will
not have to change the gain settings on their mixers to produce the same sound level.
2. The input sensitivity will be different for each power point. It takes more input voltage to drive a
larger amp of the same gain to its higher power output.
3. The scheme becomes awkward when coupled with fixed level outputs, such as most digital sources.
Suppose you have a D/A set up to comfortably drive a "500W" amplifier. If you upgrade to a
"2000W" amplifier with the same gain, you will need 6dB more signal and this may not be
available from the source. As powers increase, this problem becomes more acute.
4. The noise floor will be constant, and changing to a more powerful amp will not increase feedback.
5. The PLX series uses a 32dB gain structure, which matches some other high power retail
competitors, and provides enough gain to work comfortably with any source.
So, be careful when choosing the right amplifier for your system. In fact, you may want to be more
‘sensitive’ to your amplifier’s inputs…

Also read here
http://www.qscaudio.com/support/library/papers/puzzle.pdf

Tad more info to help understand amps. Not directly related to original question, but thought it worth noting.

[Tony Scott]

Q: Is there an ‘industry standard’ for the input sensitivity level of professional power amplifiers?
• A: The answer to this question is regrettably ‘NO’. There are two different schools of thought -- design
with a constant input sensitivity, or design with a constant gain. This makes it difficult to substitute
amplifiers within a system – the user must first understand the amplifier’s gain structure.
When different amplifiers are used within a system, there should be negligible auditory differences
(aside from overall loudness, of course). However, mismatches can occur when an amp with a different
gain structure is introduced into a system. This could result in the notion that replacement is “not as
loud” or “distorts too easily”, when, in reality, the variation is due to different manufacturer having
different policies about input sensitivity.
The first school of thought sets the input sensitivity (signal level required for full output) of all models
to the same value, regardless of power. This policy is used on the RMX, ISA, CX, PL2, and
PowerLight series. The results of this policy are:
1. The relative "loudness" of two different amps will track their power ratings. A more powerful amp
will sound louder than a smaller model, but all the amps will clip at the same input level.
2. The gain will be different for each power point. (This is a direct consequence of holding the input
sensitivity constant.)
3. The input headroom will always be the same for fixed level sources. This makes it easy to connect
different power amplifiers to a given line level, but by the same token, a larger amp will sound
louder and amplify any noise floor by a greater degree.
4. Even within the “constant sensitivity” realm there are differences. Popular sensitivity levels
include: 0.775 (0dBm), 1.0V (0dBv), and 1.23V (+4dBm). As powers have increased, QSC has
settled on an input close to 1.23V (+4dBm) to reduce the noise floor.
The constant gain concept (as used in QSC’s PLX amplifiers) keeps the gain (the degree of
amplification) the same for differing power levels within a series. This has the following results:
1. Amps of different powers sound "equally loud" -- buying extra power results in extra headroom,
not more volume. Therefore, a larger amp will "clip later" than a smaller amp, but operators will
not have to change the gain settings on their mixers to produce the same sound level.
2. The input sensitivity will be different for each power point. It takes more input voltage to drive a
larger amp of the same gain to its higher power output.
3. The scheme becomes awkward when coupled with fixed level outputs, such as most digital sources.
Suppose you have a D/A set up to comfortably drive a "500W" amplifier. If you upgrade to a
"2000W" amplifier with the same gain, you will need 6dB more signal and this may not be
available from the source. As powers increase, this problem becomes more acute.
4. The noise floor will be constant, and changing to a more powerful amp will not increase feedback.
5. The PLX series uses a 32dB gain structure, which matches some other high power retail
competitors, and provides enough gain to work comfortably with any source.
So, be careful when choosing the right amplifier for your system. In fact, you may want to be more
‘sensitive’ to your amplifier’s inputs…


So what this is saying, put simply is that some amplifiers need either a lower or higher input signal to drive them than others?

and

that ignoring this requirement can lead to either distortion if signal is too high for the amp or noise and poor performance if the signal is too low for the amp?

Is this right, do I win £5? :D :D

[Thames Valley Discos]

£2.50

[BeerFunk]

Because the input voltage is reduced by the transformer the wattage output can be increased ALLOWING MORE WATTS TO BE PUT OUT THAN ARE BEING PUT IN BUT AT A LOWER VOLTAGE. :)
Yes, but it's all relative, my example was simplified to highlight the efficiency of the amp. You're not really getting any more power out of the amp than you're putting in... well, 'power' is a poor term to use, as technically you are - so we'll say 'energy' :)

[Tony Scott]

Yes, but it's all relative, my example was simplified to highlight the efficiency of the amp. You're not really getting any more power out of the amp than you're putting in... well, 'power' is a poor term to use, as technically you are - so we'll say 'energy' :)

Yeah agreed you get no more 'Energy', be a neat trick if you could. :D

I was just trying to explain to Rob how it is possible to get higher watts coming out of an amplifier than the watts going in. Do you think it worked? :)

ROB!.......have you got it yet mate? :D

[rob1963]

I was just trying to explain to Rob how it is possible to get higher watts coming out of an amplifier than the watts going in. Do you think it worked? :)

ROB!.......have you got it yet mate? :D

Tony...the jury is still out on that one...although I AM trying!

I don't like words such as "energy" or "power", as they are pretty meaningless, so let's talk watts.

If an amp has a power requirement of 1,000 watts, that means it draws 1,000 watts from the mains. Therefore, I'm still struggling to understand how it can have an output of say 2,000 watts.

Don't worry about it guys, I'm just a bit thick on technical issues!

Move along please, there's nothing to see here!

:D

[Excalibur]

Tony...the jury is still out on that one...although I AM trying!

I don't like words such as "energy" or "power", as they are pretty meaningless, so let's talk watts.

If an amp has a power requirement of 1,000 watts, that means it draws 1,000 watts from the mains. Therefore, I'm still struggling to understand how it can have an output of say 2,000 watts.

Don't worry about it guys, I'm just a bit thick on technical issues!

Move along please, there's nothing to see here!

:D

Don't worry mate, the national grid are waiting for the answer to that one! Could save them about £20 million a year!
Seriously the link posted earlier explained how you could get peak output higher than your input, but and I have resisted posting this before, YOU CANNOT GET MORE POWER OUT THAN YOU PUT IN, NO MATTER WHAT VOLTAGE YOU STEP IT UP OR DOWN TO. To quote the wisdom of " Star Trekkin" :- "Ye canna change the laws of physics":bang:

[BeerFunk]

Yeah that's right, I didn't really read what Tony had put :o

If you step down the voltage, you would have to increase the current to maintain the power, as power is a product of current and voltage (P = I x V)

[Jiggles]

This is helpful! http://sound.westhost.com/amp-basics.htm

[Excalibur]

Yeah that's right, I didn't really read what Tony had put :o

If you step down the voltage, you would have to increase the current to maintain the power, as power is a product of current and voltage (P = I x V)

Hallelujah!

[Thames Valley Discos]

http://www.maplin.co.uk/Module.aspx?ModuleNo=38343&C=Maplin&U=SearchTop&T=POWER&doy=19m7
as mentioned before, get one of these, they are really usefull.

[BeerFunk]

This is helpful! http://sound.westhost.com/amp-basics.htm
Is it? In this context? Can you quote the relevant section for us then, because I can't be bothered to read through it all!

[Jiggles]

Is it? In this context? Can you quote the relevant section for us then, because I can't be bothered to read through it all!

Well i found bits of it on how the wattage is worked out!



Amplification Basics
The term "amplify" basically means to make stronger. The strength of a signal (in terms of voltage) is referred to as amplitude, but there is no equivalent for current (curritude?, nah, sounds silly). This in itself is confusing, because although "amplitude" refers to voltage, it contains the word "amp", as in ampere. Maybe we should introduce "voltitude" - No? Just live with it.

To understand how any amplifier works, you need to understand the two major types of amplification, and a third "derived" type:

Voltage Amplifier - an amp that boosts the voltage of an input signal
Current Amplifier - an amp that boosts the current of a signal
Power Amplifier - the combination of the above two amplifiers
In the case of a voltage amplifier, a small input voltage will be increased, so that for example a 10mV (0.01V) input signal might be amplified so that the output is 1 Volt. This represents a "gain" of 100 - the output voltage is 100 times as great as the input voltage. This is called the voltage gain of the amplifier.
In the case of a current amplifier, an input current of 10mA (0.01A) might be amplified to give an output of 1A. Again, this is a gain of 100, and is the current gain of the amplifier.

If we now combine the two amplifiers, then calculate the input power and the output power, we will measure the power gain:


P = V x I (where I = current, note that the symbol changes in a formula)

The input and output power can now be calculated:

Pin = 0.01 x 0.01 (0.01V and 0.01A, or 10mV and 10mA)
Pin = 100uW
Pout = 1 x 1 (1V and 1A)
Pout = 1W


The power gain is therefore 10,000, which is the voltage gain multiplied by the current gain. Somewhat surprisingly perhaps, we are not interested in power gain with audio amplifiers. There are good reasons for this, as shall be explained in the remainder of this page. Having said this, in reality all amplifiers are power amplifiers, since a voltage cannot exist without power unless the impedance is infinite. This is never achieved, so some power is always present, but it is convenient to classify amplifiers as above, and no harm is done by the small error of terminology.

[Tony Scott]

rob1963 asked how it seemed possible to have an amplifier that had an output wattage rating higher than it's input wattage rating.............

.......... an example to prove I'm not totaly crazy! :)

I've just ordered a new toy, Crown XTi4000:http://www.crownaudio.com/amp_htm/xti.htm

As we can see from the spec sheet the XTi4000 will draw a maximum current of 8amps from the 230volt main electricity supply.

To work out the maximum amount of watts mains electricity this amp will use we simply multiply the maximum current drain (8amps) by the supply voltage (230v).

so

8 x 230 = 1840

therefore at maximum power output the XTi4000 will use 1840watts of mains electricity.

The spec sheet states that at 4ohms bridge-mono this amp will produce 3200watts.

Input 1840watts, 0utput 3200watts.

There is no magic involved it is basic electronics principle. Ohms law!

Ohms law and the laws of physics are set in stone, bit like that sword, what was it called?...........

.............nah, can't remember! :D

Anyway, ohms law works with 3 variables, AMPS, VOLTS & WATTS.

Alter any one of these 3 variables and it effects the other two.
They are all relative to each other so at a lower Voltage and higher Current drain it is possible to increase the Watts but still use the same amount of energy.

Edit note: This is all done on the Secondary side of the transformer so has no effect on the maximum current drain (8amps) of the primary 240v mains side. It does obviously increase the current drain on the secondary.

I love you all. :)

[Thames Valley Discos]

You will find that maximum current draw is when amp is run with heavey clipping. In normal use they use 2-3 Amp.

[Tony Scott]

You will find that maximum current draw is when amp is run with heavey clipping. In normal use they use 2-3 Amp.

Yes I agree and my post has been edited to show this. :)