Power consumption


Well-Known Member
Looking around for a new stereo receiver/tuner, I've noticed the power consumption figures of various products. My own Onkyo AV receiver used for TV and radio shows a consumption figure of 620w.
My question is this:
Is that figure the maximum it will consume if, say, all speakers are engaged and the TV and DVD player is on?
If only the tuner and a couple of speakers are used, is the wattage required reduced?
Seems likely to be a max as power input usually has some sort of proportionality to power output. I'm surprised that, in these 'green' days, they don't give more typical values though.
If you're looking on the mains label on the device itself, it has to show the maximum power demand. Check the manual where the max and typical figures should be quoted.
The power consumption figure came from the manual and the only other figure mentioned is the 'Maximum effected power output' of 7ch x 175w @6 ohms.

Logically, I would assume that power consumption is based on the amount of equipment in use at any one time, but I'd hate to think I am using, say 300 watts, just to listen to the radio, despite the fact that the quality of sound is superior to a stand alone radio. Coupled with the fact that we have a second receiver in another room on around 8hrs per day.
Hard to say. What model is it?

The quiescent power consumption depends on the technology. If the amplifiers are Class A the quiescent power will be much higher than (say) Class D. (Class A is a high quality linear output stage but with a large current flowing through the drivers even when the are doing nothing, Class B reduces the quiescent current but introduces a little cross-over distortion which has to be compensated by negative feedback IIRC, Class D uses digital PWM techniques to reconstruct the waveform by low pass filtering).

I have a cheap mains power meter - you plug the device under test through it and it tells you (roughly) what current/power the device is using. An even rougher (but practical) test is to see how warm it is - if there is a lot of heat being dissipated, there is a lot of power going in.
Onkyo TX-SR608.

Quiescent-I had to look that one up! :) As to the rest, much as I appreciate the response, I maybe wish I hadn't asked! ;)

However the Onkyo (not classed as far as I can see, probably as it is an AV receiver) runs very cool with just the tuner on, but my 24 year old Technics Class A stereo amp runs very warm after a few hours just clipped to a Technics tuner.
Cheap mains power meter sounds just the ticket.
I have a Sony 5.1 Amp. that has 5 X 110Watt channels, with the volume set to zero the measured power consumption is 70Watts (a lot higher than I would have guessed) this figure only goes up to 72 for a normal listening level (driving all 5 channels), so most of the power is quiescent current. If you do want to get a power meter I would suggest the Maplin L61AQ, this is £20, I have two cheaper power meters but neither of them measure the power factor correctly. Without getting too technical if it doesn't correctly measure power factor it will give a falsely high reading because it is really measuring VA even though it will call it Watts, you only pay for 'real' Watts not for VA Watts. As an example the other cheaper power meters both incorrectly show the 'Watts' as 100W when it is really 70W
I wonder what "40 FM/AM Random Presets" means.

If the TX-SR608 is Class A (and reading between the lines on the spec sheet it looks like it might be - lots of words but it doesn't say much that's technically important), then the quoted 620W is probably close to what it draws all the time (which is how Class A achieves its low distortion figures). The standby figure is pretty low though.
If my 10 channel amp with 9 rated at ~100w and the other feeding a 350w sub used that much all the time, I would need to open a window to let the heat out.
From what I can see of the Onkyo TX-SR608 spec it's not going to be class A, the high power consumption is misleading. My Unison Research S6 amp is class A and uses about 265w to output about 35w to the speakers. But is is purely a stereo audio amp ( though you can also make toast on it after an hours playing ).
The Onkyo is an AV receiver so has multiple channels, tuners, video processors and all the fripperies you young folk like. Hence the high max power consumption. But does it make toast?
:D I love the 'young folk' bit!
I am thinking that I should have stuck to my original plan and bought a stereo amp with tuner. It's beginning to irk me somewhat that I may be using 625W to listen to the radio!
A cheap power meter will tell you. You basically have lots of different devices in one box. And without doubt a more efficient amplifier than a class A one. So I think it is highly unlikely you are using anything like 625w to listen to the radio.
Class A is fantastic for high quality audio in part because you have full power on tap all the time to go from pianissimo to fortissimo without distortion or delay. Other classes have to use big expensive capacitors to get close, and most don't bother. But class A is a bit like driving with your throttle foot hard down and the other foot on the brake.
socrates is a dog learning to drive???

Thanks Socrates, I mentioned previously that I do have a class A stereo amp which is used extensively and this does run pretty warm. ( Technics SU-X955, over 20 years old.)
The Onkyo however is still cool to the touch even after many hours of tuner use. I tested it also using Internet radio though the FoxT2, it gets maginally warmer. This receiver drives a pair of Acoustic Energy AE1 floorstanders.
Ah, so you did. Should have spotted that.

Though I have to tell you Technics "new Class A" was actually a marketing label, and its not really class A at all. But well reviewed as I recall. I think it may have used a class A pre-amp but the power amp was class B. Class a isn't just warm - if you touch it you risk leaving your finger tips behind!
Marketing label? I thought that all pre-amps were class A and it was only the power output stage that they made class B to reduce quiescent power used in a class A power O/P stage.
Yes, marketing label. Shocking isn't it? Technics also had a class AA. Like class A but double plus good! The key was in the "New" class A. In my experience "New" generally means "Not". Remember New Labour?

You may well be right about the pre-amp stages. Class A is normally used with reference to either power amps or integrated amps in which case it means the whole system is class A. Which means lots of money and lots of heat. Apart from anything else you wouldn't want to put too many other components into the same box as a class A amp as they would cook.