Some observations about amplifier power consumption figures

[vasishta.sushant]

About a couple of weeks ago, I bought this Cambridge Audio 550A stereo amplifier, purely based on the sound output. Only when I took it home, I realized that I made a blunder. No nothing bad with the sound output but while connecting my rig, I read the power consumption figures at the back panel of the amplifier. It said 500W

Truly it was a maddening experience. For just 60W of output the unit was consuming 500W whopping watts of power. This made me so sick that I started listening to it as less as possible. Even when I was trying to enjoy my music, I just had this "Month End Power Bill" thing always going on top of my head.

Finally I thought of investigating this a bit deeper and the results were somehow not convincing and in fact very confusing.

I just used a digital clamp-meter to find the current usage by the amplifier and multiplied it by 250 (220V and some for the power factor). Here are the results that I found:

1) On standby the meter read 0.00, which is pretty much inline with the less than 1W stand by power consumption listed in the manual.
2) On usage (at around 9-10PM volume mark, which is mostly what I prefer) the meter reading was always less than 0.15. Now this thing translates to odd 38W of power consumption.

To double check, I used the same strategy to find out the power being consumed by some other appliances and I could fairly estimate the correct usage. e.g. my room cooler(No AC yet ) was consuming 150W which is correct. My netbook was consuming 40W which is what the power brick reads. I did few more as well just to make sure that the clamp-meter and the strategy being employed were fine.

Now where is the disconnect ? 500W on the back panel and consuming less than 10% of that in the real world.

The exercise has left me a lot more relieved of the annoying feeling but still left me wondering whats going on. You guys wanna comment ?

 

[reignofchaos]

It'll probably eat 500W peak when something really loud plays for a fraction of a second.

 

[Kittu]

+1 to ROC, I did the same testing last week. It was going to the peaks when it was playing loud and much less when the sub was off .

 

[vasishta.sushant]

Actually I tried to play it loud as well. Like 10% above my maximum limit (again that was less than 12'O clock on the volume knob). Even then the consumption didn't cross 0.2. Something is surely missing.

And I am not using any sub. Its just the amplifier coupled with the Polk Audio TSi300. Strange. Very strange. I am surely not convinced that rolling the volume even more will increase the power consumption to 500W. Even if I project the usage pattern logarithmically, It would be like 150W max.

 

[jai1611]

500w is most probably the size of the transformer that the amp has. Its very rare for an amp to be utilising close to the full rated power unless it runs in Class A

 

[vasishta.sushant]

I just can't express how comfortably relieved I am right now seeing that my total power consumption (netbook+Amplifier), at a very very comfortable listening volume has not even increased beyond 0.42 on the clamp-meter. Thats less than 100W

Now I am thinking that I should have bought the 650A instead.

 

[venkatcr]

I think there have been numerous nomenclature confusion.

What an amplifier will say at the back is Maximum Power Consumption of xxx Watts. What this means is that the amp MAY draw an maximum current of xxx Watts from the power supply. Power consumption is used not only by the audio generated by the amplifier, but also by the heat generated.

Secondly, if you take a audio signal it is actually a sine wave with peaks and troughs. The calculation is always done with a continuous peak output at the worst possible resistance from speakers. If you amp say 60 watts per channel into 8 ohms, we are talking about a total of roughly 240 watts into 4 ohms, and possibly 440 watts into 2 ohms. These are not correct figures but mentioned just as an example.

In reality, an amplifier will never consume what it says at the back as it can never deliver those kind of amplitude figures before it starts clipping and your ears start ringing. They usually can deliver 1/3rd to 1/4th of those figures. But in test conditions, when pushed to the full, the amplifier could draw those kind of figures.

Secondly if you measure an amplifier's output at the speaker terminal, you are not measuring actual power consumptions due to amplifier deficiency. Class A,B, and C are all notoriously inefficient. If you measure power consumption at a 10 watts output, the amplifier may actually be consuming close to 3 or 4 times that.

The power consumption figures at the back should actually be read as 'max power requirement' at worse case scenarios.

Cheers

 

[vasishta.sushant]

I understand what you are saying but here I am measuring the "actual" measurement at the wall outlet. I am already measuring using 8ohms speakers so I dont care what would be the figures at other resistance levels.

At 8ohms, the consumption is less than 10%. This means something. When they intially stated those figures, I wonder how did they measure ?

My only trouble is why the hell these figures written on the back are so highly rated.

 

[Bobby]

This made me so sick that I started listening to it as less as possible. Even when I was trying to enjoy my music

Oh man, i really loved your statement Anyways, its quite obvious to turn moonstruck knowing your amp is continuously consuming 500 watts of power.

 

[pannags]

Hello,

Revoking an old thread, but invoked a lot of interest as I was equally panicky while estimating the amount of power consumed in my setup, in which all sources (Cable STB, DVD player) are connected to my Onkyo TXSR608.

The Onkyo, processes the inputs and drives a pair of Wharfedale fonts (yes. only 2 spkrs at the moment) and an LCD TV through HDMI.

Basically, the TX-SR608 has to run to be able to listen to music or view video from any source.

Now here are my questions:

1. Have I understood it correctly that the power consumed by the AVR depends on the "real" load and is never really close to the labeled rating?

2. Does the fact that I have only 2 speakers connected mean that the power consumed is even lower than with a full fledged 5.1 setup (Since its driving only 2 sources)? (Though this will not prevent me from adding a sub and a center shortly)

3. Does a similar principle hold good with plasma TVs (since they are self lighting and consume as much energy as they have to display) as against CCFL/LED LCDs, which consume constant power?

Many thanks for you answers. Will help with with my decision on whether a plasma will add too much carbon footprint to my account

Cheers,
Pannags

 

[anuragn]

Hello,

3. Does a similar principle hold good with plasma TVs (since they are self lighting and consume as much energy as they have to display) as against CCFL/LED LCDs, which consume constant power?

Many thanks for you answers. Will help with with my decision on whether a plasma will add too much carbon footprint to my account

Cheers,
Pannags

Just what I was thinking. Can somebody check the actual power consumption of a plasma vs the max power rating? Would really help a lot.
We have seen hundreds of debates regarding power consumption of LCD vs Plasma, all in theory.

 

[sudhir_rr]

A stereo 60W AB amplifier designed to work with 8Ohm impedance will typically consume about 150W power. Here is how -
60W - output power
10W - Consumed by output transistors
--------
70W
* 2 - two channels
-------
140W
10W consumed by power supply components - transformer and diodes.
--------
150W.

The catch here is that this is valid only for a resistive load, which doesn't change. Speaker's rated impedance is calculated at 1kHz frequency. It varies a lot and could go down by as much as 40%. When that happens amplifier not designed for the lowered impedance will fall short of power.

So typically amplifier designers make designs at rated impedance and add additional power to take care of lower speaker impedances. There is no standard for this, so it's upto an amplifier designer to support whatever their brand usually does.

Cambridge audio's Azur 550A's webpage doesn't specify what's the lowest supported speaker impedance. Check this webpage for a NAD amplifier, it states this very clearly.

2 x 150W Continuous Power into 4 Ohms and 8 ohms
200W, 365W, 500W IHF Dynamic power into 8, 4 and 2 ohms, respectively

C 375BEE Integrated Amplifier - NAD Electronics

 

[reignofchaos]

A class AB can have theoretical maximum efficiency of roughly 78.5%. In practice, most amps are biased into class A for the first few watts where the amp stays most of the time. This also reduces peak efficiency significantly and you'd only be getting 50-60% efficiency most of the time. The peak power consumption will be significantly more than what you seem to account for.

However the average power consumption would be a lot less than what you seem to be accounting for. It'll mostly be decided by how far into class A the amp is biased into.

 

[jaudere]

Very interesting thread indeed.
I have marantz pm 6002 rated 45X2 at 8 ohm and 60X2 at 4 ohm. It's power consumption is specified as 130w.
My book shelves are 4 ohm. I very rarely cross 9 o'clock position of volume knob and never need anything beyond 10 o'clock.

Based on this, Can we make a guess what could be the actual power consumption? This is just out of curiosity.

Another interesting comparison: CA 550 Rated power consumption is 500w and it gives 50w RMS /ch. Marantz pm6002 has rated power consumption 130w and provides 45w RMS/Ch.
Does it mean that the headroom in CA 550 is much better even if RMS Rating of both the amps is quite similar?

 

[amol12]

vasishta.sushant,
What model of digital clamp meter you have? I am thinking of buying one as I am curious of power consumption of many appliances!

 

[cricfansd]

Just what I was thinking. Can somebody check the actual power consumption of a plasma vs the max power rating? Would really help a lot.
We have seen hundreds of debates regarding power consumption of LCD vs Plasma, all in theory.

Plasma TV power is dependent on the content it plays. When the screen shows all white at max brightness it consumes the max rated power. Typical scene is on average 30% of max power. Once upon a time I had measured the power consumption of Plasma TV over 7.5 Hrs of our database video files and the average was around 30-35%. At that time LCD with CCFL dimming could lower the power consumption to around 55-60% of max power. LCD with 2D LED dimming with around 128 dimmable block had brought it to plasma level though max power consumption of plasma is higher than similar sized LCD TV.

 

[reubensm]

About a couple of weeks ago, I bought this Cambridge Audio 550A stereo amplifier, purely based on the sound output. Only when I took it home, I realized that I made a blunder. No nothing bad with the sound output but while connecting my rig, I read the power consumption figures at the back panel of the amplifier. It said 500W

Truly it was a maddening experience. For just 60W of output the unit was consuming 500W whopping watts of power. This made me so sick that I started listening to it as less as possible. Even when I was trying to enjoy my music, I just had this "Month End Power Bill" thing always going on top of my head.

Finally I thought of investigating this a bit deeper and the results were somehow not convincing and in fact very confusing.

I just used a digital clamp-meter to find the current usage by the amplifier and multiplied it by 250 (220V and some for the power factor). Here are the results that I found:

1) On standby the meter read 0.00, which is pretty much inline with the less than 1W stand by power consumption listed in the manual.
2) On usage (at around 9-10PM volume mark, which is mostly what I prefer) the meter reading was always less than 0.15. Now this thing translates to odd 38W of power consumption.

To double check, I used the same strategy to find out the power being consumed by some other appliances and I could fairly estimate the correct usage. e.g. my room cooler(No AC yet ) was consuming 150W which is correct. My netbook was consuming 40W which is what the power brick reads. I did few more as well just to make sure that the clamp-meter and the strategy being employed were fine.

Now where is the disconnect ? 500W on the back panel and consuming less than 10% of that in the real world.

The exercise has left me a lot more relieved of the annoying feeling but still left me wondering whats going on. You guys wanna comment ?

I had the same experience with my NAD 216thx. It is a huge power amp and is supposed to consume over 500 watts. I actually wrote to NAD and they came back telling me that it was the power consumption rating based on the amp running at full throttle in bridged mode into a 4 ohms load, pumping out about 800 watts of dynamic power. I was absolutely pleased to hear this. I play it a lot every day (in 2-channel mode, and obviously not that loud) and there has been no notable change to my electricity bill

 

[sudhir_rr]

Another interesting comparison: CA 550 Rated power consumption is 500w and it gives 50w RMS /ch. Marantz pm6002 has rated power consumption 130w and provides 45w RMS/Ch.
Does it mean that the headroom in CA 550 is much better even if RMS Rating of both the amps is quite similar?

Amplifier efficiency by power consumption shouldn't be treated like a figure of merit. Amplifier efficiency depends on a variety of factors such as BJT or MOSFET, complimentary or quasi-complimentary, voltage drop across output devices to name a few. So higher power doesn't necessarily mean better amplifier. Similarly higher power doesn't imply higher headroom.

Headroom of an amplifier in fact can't be more than 10% of maximum sustained power at <1% distortion. That's where it starts clipping and results in huge distortion.

Speakers on the contrary can have even 3 times the nominal power handling for headroom.

 

[trittya]

Very educative, indeed, thanks a lot, Gents.

 

[jaudere]

Let me revive this thread again.
I recently bought a power amplifier. i did not notice what was written at back when buying.Later I read it at the back panel: 1000W. I bought it basically because I got it cheap and I am planning to set secondary system.

Now , it is a power amplifier. Does not have gain control. Volume is controlled by volume on PC (will soon be getting a preamp). It is probably class B or AB (does not get much hot even after 2 hours of listening, so the class of amp is a guess.)

Now, since it does not have gain control, how much electricity it is likely consuming? I don't know how many watts it is pumping into my speakers. My speakers are of very high efficiency: 97dB/watt/m and I sit at 8 feet from speakers. So I am sure that I need less than 10watt (even 10 is I think on higher side) to make my speakers very loud. I don't have patience and knowledge to use tools to measure the electricity consumption.

Secondly, if I keep the power amp on but do not play any music/sound, does it consume any electricity? The amp probably does not have speaker protection circuit and gives a big thud to the speakers while switching on. It does not have stand by. I am searching for protection kits but till I get a circuit, I tend to keep it on.