power consumption vs RMS rating of amps

[svenkateshsmart]

Hi,

You will find the explanation in http://www.hifivision.com/home-theater-box/2888-almost-scared-2.html

Pls do search before creating threads.

Cheers!

 

[vu2oro]

Hi,
say the total power consumtion of a stereo amp as listed in the spec sheet is 100watts, you may expect to get 27-30watts rms each channel before clipping starts.
Cheers...

 

[vu2oro]

Of course, this is assuming the amp is class AB, and not pure class A where it is much lower or class D where it is significantly higher, but of course less than 100W.

 

[venkatcr]

say the total power consumtion of a stereo amp as listed in the spec sheet is 100watts, you may expect to get 27-30watts rms each channel before clipping starts.

say the total power consumtion of a stereo amp as listed in the spec sheet is 100watts, you may expect to get 27-30watts rms each channel before clipping starts.

I don't understand what you are trying to say here. Power consumption has nothing to do with clipping. If a amplifier is rated at 100 watts and start clipping at 27-30, I would say it is one of most pathetic design unless, of course, you are using it with very difficult to drive speakers.

Cheers

 

[venkatcr]

thank you for posting the link. but i didnt got it clearly.is any other simple answer is there?

In power consumption there are multiple terminology you have to understand.

The basic unit of enregy is called a Joule (j). Joule is a very small unit of measurement. In regular usage, an electrical unit's power consumption is measured in watts (W). A Watt takes up 1 Joule of energy every second. So for every minute of usage, a 1 watt unit consumes 60 joules.

In electrical circuits there are two more terms you have to be aware of. One is Voltage (v) and the other is current referred to as Ampere (A). The power delivered by the electrical circuit is measured as a product of volatge and current. Thus 1 watt is equivalent to 1 volt Ampere is equivalent to 3600 j (1W = 1vA = 3600j).

Power consumption is measured in what is called kilo watt hours (1kWh). In other words, this is the amount of energy (jopules) that a 1 watt unit consumes when it runs for 1000 hours. This, in energy terms, is equal to 36,00,000j or 3600 kilojules.

Your electricity board or company charges you for every 'Unit' of power that you consume. A 'Unit' is 1kWh.

An amplifier has two ratings - One is the amount of energy or power it consumes when it is idle. The second is the amount of energy or power it consumes when it is running. This is measured by the power wattage speficied in the amplifier.

If these are clear to you, please ask a specific question that is confusing you.

Cheers

 

[thekinge]

Venkat, Thanks for your post and I do have a couple of specific questions. The total power consumption of the Onkyo TX-SR608 I recently purchased is 620 Watts. It is also mentioned in the back panel as a Class B device so I assume it is a class B amplifier. Now the maximum efficiency of a Class B amplifier is approximately 79%. Assuming this receiver provides the maximum efficiency of 79%, then my understanding of the power available per channel is:

1. Maximum power output from the receiver (for all channels) ~= 490 Watts
2. Maximum Watts Per Channel (WPC) for 5 channel usage, all channels driven = 98 Watts
3. Maximum WPC for 7 channels usage, all channels driven = 70 Watts
4. Since there is a separate subwoofer pre-out in my receiver, I assume that the receiver would not be spending any of its available power in processing LFE signals and would just pass them as line level outputs to the subwoofer.

Is my understanding correct? And if it is correct, I have a second question.

AVRs from Marantz & Denon mention "discrete amplification" for each channel, but then if I multiply the Watts Per Channel provided by these receivers, it doesn't add up vis-a-vis the total power consumption. For example, the Denon AVR-1910 mentions that the output watts per channel is 90 Watts. So even in a 5.1 channel usage, it means that it has to consume at least 450 Watts to be able to output 90 WPC and that is without taking the receiver's consumption vs. output efficiency into consideration. But the power consumption of 1910 is only 430 Watts so there is no way it can output 90 Watts Per Channel all channels driven. But then Denon mentions that the 1910 supports 90 Watts Per Channel and then "discrete amplification" for each channel. What is the correlation? Or is it just a marketing gimmick from Denon?

 

[moktan]

In power consumption there are multiple terminology you have to understand.

So for every minute of usage, a 1 watt unit consumes 3600 joules.

Cheers

sir , isn't it 60 joules when a power of 1 watt works for a minute...maybe you were talking about an hour??? or perhaps you were talking about a 1 kilowatt unit??? since 1watt is a joule of energy per second...

 

[ajinkya]

Is my understanding correct? And if it is correct, I have a second question.
For example, the Denon AVR-1910 mentions that the output watts per channel is 90 Watts. So even in a 5.1 channel usage, it means that it has to consume at least 450 Watts to be able to output 90 WPC and that is without taking the receiver's consumption vs. output efficiency into consideration. But the power consumption of 1910 is only 430 Watts so there is no way it can output 90 Watts Per Channel all channels driven. But then Denon mentions that the 1910 supports 90 Watts Per Channel and then "discrete amplification" for each channel. What is the correlation? Or is it just a marketing gimmick from Denon?

Yes, your understanding is correct. Regarding your second question: Does the Denon manual mention "90 watts per channel all channels driven"? If not, then the 90 watts could be the measured output when only one (or some subset of channels are driven). So, please check that and post your observations. If it does say "all channels driven" then something is wrong with the ratings.

My understanding of "discrete amplification" is that each channel (5 or 7) has its own power amplifier section. That does not mean they have separate transformers. Only that the power amp section is separate. If you look at the picture of an open 1910, you'll see what I mean. Here is a link for a detailed explanation: difference between integrated and discrete amplification - Page 2 - Audioholics Home Theater Forums

 

[venkatcr]

thank you for all. what my specific question is that "you got new amplifier -you dont know any ratings of the amplifier.in the back plate it is written as -powerconsumption-600watts.suppose if it is 2channlel amplifier then how much is the rms wattage of each channel?if we think the amp runs at Class AB.

The correct representation of an amplifier power output is the energy is needs to generate a continuous average sine wave. This is called sine wave power, and most times just shown as Watts.

RMS or root mean square is actually (1/?2)*X of sine wave power peak X. This makes some sense when there is no resistance. A loudspeaker is continuously providing resistance to an amplifier. RMS is erroneously used to describe average power and should be ignored.

What you should look for is not the power consumption written in the back, but the power the amplifier can actually generate. This will be in the manual and shown as xx watts per channel. You multiply that figure by the number of channels to get the power capabilities of the amp.

Cheers

 

[venkatcr]

sir , isn't it 60 joules when a power of 1 watt works for a minute...maybe you were talking about an hour??? or perhaps you were talking about a 1 kilowatt unit??? since 1watt is a joule of energy per second...

You are correct. I have edited my post,

Cheers

 

[venkatcr]

Is my understanding correct? And if it is correct, I have a second question.

AVRs from Marantz & Denon mention "discrete amplification" for each channel, but then if I multiply the Watts Per Channel provided by these receivers, it doesn't add up vis-a-vis the total power consumption. For example, the Denon AVR-1910 mentions that the output watts per channel is 90 Watts. So even in a 5.1 channel usage, it means that it has to consume at least 450 Watts to be able to output 90 WPC and that is without taking the receiver's consumption vs. output efficiency into consideration. But the power consumption of 1910 is only 430 Watts so there is no way it can output 90 Watts Per Channel all channels driven. But then Denon mentions that the 1910 supports 90 Watts Per Channel and then "discrete amplification" for each channel. What is the correlation? Or is it just a marketing gimmick from Denon?

Your understanding is correct. And there is a combination of marketing talk as well as facts in the calculation.

When an AVR is functioning alone it is actually not creating any energy whatsoever (1). Only when you connect a set of speakers does the amplifier actually starts drawing electrical power and creating sound power.

It is very difficult to measure the power output and power consumption of an amplifier when it is connected to a speaker as the frequencies keep varying and each frequency would need a different power for the same amp/speaker combination. So what manufacturers do is to make the amplifier generate a tone at a fixed frequency of 1000Hz for a little while. When this is happening, the power output of the amplifier and it's consumption are measured. This is what usually mentioned in the specs.

When you are actually playing music or watching a movie the frequencies keep changing. When this happens, the load on the amp also changes. The best one can do in a situation like this is to measure for a certain period of time and work out an average. This is never an accurate figure.

Manufacturers with some repute would ensure that the power handling capability specified would be at the bottom end of the average so that the amp's capability are actually higher. And it is vice versa for power consumption.

Speaker impedance and resistance also are important. So manufacturers would usually say xx watts into y ohms.

Cheers

PS.

(1) When an amp is not connected to speakers and is powered on, there are electrical circuits inside the amp that does consume power. This is called power consumption when idle. Thanks to Ajinkya.

Cheers

 

[ajinkya]

When an AVR is functioning alone it is actually not creating any energy whatsoever. Only when you connect a set of speakers does the amplifier actually starts drawing electrical power and creating sound power.
Cheers

Venkat,
Not strictly true. Whenever an amp is on standby or powered on, there is always an idle power draw to bias the circuits. This power draw could range from very small (Class D) to constant, full power (Class A). When a load is connected, then the power draw changes with the impedance presented by the load to the amp output stage.

 

[venkatcr]

Not strictly true. Whenever an amp is on standby or powered on, there is always an idle power draw to bias the circuits.

You are right and many brands show this separately as power consumed when idle. But this amount is the power drawn by the amp and is usually very small. What I was talking about is the energy created by the amp or it's output.

Cheers

 

[NetFreak]

the power ratings and power consumtion of the amp is not matching.

These will never match.

Amp would convert a lot of energy to heat and it would not go to speakers. So, if power consumption in 700 watts, RMS output (sum of RMS of each channel) would always be less than 700.

 

[odyssey]

Hi
Its hard to answer this question exactly but let me take a stab at it-
if its 600 W total power consumption and a Class AB I could generalise along the lines of
1. Power supply efficiency is 80% give or take which means that the net power after the power supply stage is about 480W
2. Out of the 480W, assume an efficiency of 50% for the Class AB (which is probably which brings it down to about 240W

remember that this is all generalisation, it depends on the PSU efficiency and the class of the amplifier efficiency, bias, etc

In all likelihood the amp is at least giving you 150W per channel

cheers

 

[venkatcr]

Sridhar, I hope you are talking about 600 Watts RMS delivering 150 Watts? If not, our belief in most manufacturers including people like NAD and CA who are famous for quoting less than what they can actually deliver, go down the drain.

Cheers

 

[odyssey]

Hi Venkat
I assume 600VA is the AC power consumption of the amp, same as RMS.

cheers
sridhar

 

[odyssey]

hai odyssey, i am supporting your statement. because my power amp(mx1000u) power consumption is 850watts.it is class A up to first 30 watts and its bios slides to class AB,when the power out put exceeds to 30watts.so if we consider its efficiencey is about 40-50% in class AB then the usefull power of 40-50%of 850watts comes to 510-425 watts. the actual RMS rating of the amp is 260x2 watts per channel.which is supporting your statement.i think this 40-50% efficiency applicable to Aand AB only.
is this correct?
cheers

Hi
Class A is lower in efficiency but it depends on the implementation. If you take a classic Class A (true class A) where the power is always the same - e.g. nelson pass Aleph series (say Aleph 3) the power consumption is 200W in total, 100W per channel, about 25W of RMS rating per channel, efficiency is 25%.

cheers

cheers

 

[sidvee]

My quicksilver mid mono tube amps have a power consumption rating of 210w each at full power, but put out only 50w at 4 or 8 ohm loads, so 25% efficiency for class a is about right - me thinks. OTOH my Belcanto s300 stereo amp. which is a digital switching design has a max consumption of 750w and an output of 300w (2 channels) into 8ohms or 600w (2channels) into 4ohms which is about 80% efficienct for a class d design. I think class a/b falls in between these two.
Cheers
Sid

 

[sidvee]

Please see attached:
Amplifier Efficiency

They are claiming Class ab at 70%
and class A at 12.5% - 22%.

Cheers
Sid