My assumptions are - If I have 70W per channel the total max output for the amp is 140W. As it is an A/B amplifier I assume the efficiency is 50% so max theoretical input power would be approx 280W?
Indeed, there’s an automotive saying “test don’t guess”. 
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I can assure you my measurements are correct, but I could not listen at max output so it’s not very relevant.
Phil
Agree😀 probably why they say typical consumption is 130W
I obtained this graph from ‘audioholics .com’ which shows the characteristic of a typical class ab amplifier. From this if I assume I typically listen at 30% of max output power ie 42W, at this point the efficiency is 30% so my input power is 140W, which is close to the 130W typical power consumption that Naim gave. It would be nice to have the actual graph for the Naim product
Unless you sometimes play extremely loudly with inefficient speakers the difference in electrical energy consumption between quiet and loud listening really is pretty minimal:
If your speakers are a fairly average sensitivity at, say, 88dB/W, and you sit, say, 4m away in a not too echoey room, and listen at a very moderate 76dB average level, your amp would be delivering only about 1 W (0.5W per channel, so maybe 1.2-1.5 W of electricity more than when Idle. (If you sit closer to the speakers less power would be used for the same loudness at your ears.) Things go up more when you get really loud - with the same speaker/room setup a 90dB average sound level, would mean your amp would be delivering about 25W (12.5W per channel), and maybe using 40-60W more electricity than when the music stops. More than a short period at that level is ear damaging territory - so thus level of power consumption shouldn’t be happening for long.
Does anyone here know how much electricity a 555PS uses just switched on please? ATB Peter
There is a whole thread on power consumption somewhere on the forum
My 555PSDR powering a 272 consume around 30W when on. (Measured)
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The actual consumption measurements I’ve done on my system (posted elsewhere on the forum) neither support your assumptions nor conclusions!
As others have said - buy a cheap meter and measure it.
Mark
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The 130W power consumption is a value given by Naim in their specification for the Uniti Star (see attached)
These were the assumptions and conclusions I was referring to.
So why not simply assume Naim’s spec is right, with actual expected to fluctuate slightly around tgat figure, but, as has been indicated by more than one responder, not by enough to be significant in terms of your energy usage at different practical volume levels?
Not sure what is incorrect Ebor. The 50% efficiency is for AB amps (see the graph I posted). The 70W per channel were max output power supplied by Naim (see the specification I attached). I agree in reality you would not listen at max power though.
Thanks IB, the Spendor A4 have a sensitivity of 86dB
I recently checked my Nova, as did Alley_Cat.
Please see: Nova on standby cost - #13 by Alley_Cat and following.
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For my calculation to estimate electrical costs that is what I have now done. The measurements other people have done on their system gives lower power so hopefully in practice mine will be lower too.
Copied from your thread “ 28-38 W while playing internet radio or from the USB-drive, with volume up to 33/100”.
Thanks. That is quite a bit lower than what Naim specify for the Nova (140W), which makes me wonder how they measured this and what assumptions are made.
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You could ask Naim Customer Service…
Working this out on paper is a fool’s errand. The sustained output doesn’t accomodate transients which can hit nearly 500w (and the transformer is designed to cope with that). The volume also doesn’t increase power, it increases gain and as such there is no linear progression of volume to power. Yes it always goes up but twice as loud is not twice as much power. In fact, twice as loud is usually many times more power but then the AB cutover masks the first part of that.
What this boils down to, which others have said is:
- If doing on paper, just go by Naims dicumented specs in the manual. Don’t bother with other calculations. The compounding of errors will just give you a number, not an answer.
- You can get an accurate answer with a wattmeter. They cost peanuts and good ones even let you program in your hourly average cost per KWh. You won’t just get a point in time readout in watts, you’ll get average watts per hour and cost per day/hour.
I used such a device months back to profile the whole house. Brilliant device. Cost $15 and in the first month saved me $200. What you think costs money and what actually cost money to run aren’t always what you imagine.
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