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Topic: Watts per channel meter (Read 8253 times) previous topic - next topic
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Watts per channel meter

Hello,

I have a separate power amp that has no illuminated power meters. I've always been curious how many watts it uses at different volume levels. What would be the best method to see the wattage it's using during certain volume levels? At a hardware store, I saw a 'Kill-A-Watt' device that plugs into the wall and then into your amp. I am wondering if this method would be accurate. Your suggestions on an external 'Watts Per Channel' device that I could add to the amp would be appreciated.

Re: Watts per channel meter

Reply #1 –
Play a 60 Hz tone and measure the output with a voltage/current meter set to AC.

Re: Watts per channel meter

Reply #2 –
The Kill-A-Watt will tell you how much (average) wall-power it's consuming.    Since the amplifier is not 100% efficient, the power to the speakers will be less than that.    At low listening levels the amp will consume much more power than it puts out....  It will consume some power with no audio signal.

Be careful with test tones because constant loud test-ones can damage your speakers.    Be especially careful with high frequencies because your tweeter can't handle as much power as your woofer.   And, you can fry your tweeter with frequencies you can't hear.

This is tricky stuff...   You really need an oscilloscope to measure the peak voltage with program material.   A multimeter will jump-around too much and it may do some kind of undefined averaging.    (From the peak voltage, you can calculate the peak power if you know the resistance/impedance.)   

Since audio typically has an approximate 10:1 peak-to-average ratio and we want to avoid clipping of the peaks, it's usually  the peaks we're interested in rather than the average output power.   

Or, if you know something about electronics you could make an attenuator and calibrate your soundcard (with a multimeter), record the attenuated signal with the soundcard, and then check the peaks with an audio editor.

Re: Watts per channel meter

Reply #3 –
Quote from: DVDdoug on
The Kill-A-Watt will tell you how much (average) wall-power it's consuming.
I understand that this is what RoyM111 is interested in. He may have held the erroneous assumption that illuminated power meters in some amps show the power that it consumes, where in reality it shows the power output to the speakers.

Measuring its power consumption will indeed require some sort of measuring tool inserted between the power outlet and the amp. I'm not familiar with the Kill-A-Watt device, and can't comment on its suitability, but it is this general kind of thing that will be needed here. I don't recommend trying to measure this with some DIY arrangement because of the safety issues involved, and also because of the difficulties arising from measuring AC power properly, with its active and reactive parts.

Re: Watts per channel meter

Reply #4 –
Quote from: RoyM111 on
Hello,

I have a separate power amp that has no illuminated power meters. I've always been curious how many watts it uses at different volume levels. What would be the best method to see the wattage it's using during certain volume levels? At a hardware store, I saw a 'Kill-A-Watt' device that plugs into the wall and then into your amp. I am wondering if this method would be accurate. Your suggestions on an external 'Watts Per Channel' device that I could add to the amp would be appreciated.

I am very familiar with the Kill-A-Watt and some competitive devices. The good news is that it is pretty accurate and measures power usage  several ways, including both power in watts and volt-amps which surprise some people by being different.  The problem I have with the Kill-A-Watt is that it has very slow response, and is pretty useless in audio systems playing music which is usually very dynamic and rapidly changing.  It has been pointed out that steady artificial test signals are required for its readings to mean anything at all. But music, even  highly  compressed music is far from being steady state, so its not clear that measurements of this kind are particularly helpful.

As others have pointed out, measuring power usage is often a whole lot less valuable than measuring actual power delivered to the speakers.  Speakers are reactive loads which means that you can't assume current or voltage from measuring just one or the other, but that you have to make rapid-responding measurements to both if you want useful information.

Re: Watts per channel meter

Reply #5 –
Quote from: RoyM111 on
Your suggestions on an external 'Watts Per Channel' device that I could add to the amp would be appreciated.

Something like this http://www.cordellaudio.com/instrumentation/power_level_meter.shtml would be needed for accuracy.
Inexpensive (very) "ballpark" http://www.vellemanusa.com/products/view/?country=us&lang=enu&id=350546

cheers,

AJ
Loudspeaker manufacturer

Re: Watts per channel meter

Reply #6 –
Note that the Velleman meter is sold as a kit so you have to solder the components onto the PC board (and you'll probably want to mount it in a box/enclosure).

I'm not sure if you can find it pre-assembled.

Re: Watts per channel meter

Reply #7 –
Thank you for all the replies so far. It's an older audiophile power amp (that says a lot right there) so the company would have probably charged hundreds more for this feature if they included it in the original design.

I've been looking at the Crown XLS Series 2 which have clipping LEDs built-in which is really nice.

The reason I posted this question about the external meters in the first place is to get a few ideas to try and save my speakers from damage from any clipping distortion that could possibly arise from the power amp during musical peaks. Blown tweeters can get expensive.

Re: Watts per channel meter

Reply #8 –
If you are at all electronically inclined, a fairly simple circuit with zener diodes and LEDs could show when an amplifier is clipping.

Re: Watts per channel meter

Reply #9 –
Quote from: RoyM111 on
Thank you for all the replies so far. It's an older audiophile power amp (that says a lot right there) so the company would have probably charged hundreds more for this feature if they included it in the original design.

In general audiophile amps and receivers universally lack proper c;lipping indicators, while they are relatively common on amplifiers for pro use.  This is a shame because a proper clipping indicator is even simpler than has been suggested here. All  it takes is a LED, 4 diodes arranged as a simple bridge rectifier, and a current-limiting resistor. In production the total parts cost is probably about $0.35.

Quote
I've been looking at the Crown XLS Series 2 which have clipping LEDs built-in which is really nice.

Not only do Crown XLS series have clippiing indicators, but they also have power level indicators.

However, level indicators are not necessarily good clipping indicators because amp clipping takes place at different voltages depending on the impedance and reactance of the speaker load.

Quote
The reason I posted this question about the external meters in the first place is to get a few ideas to try and save my speakers from damage from any clipping distortion that could possibly arise from the power amp during musical peaks. Blown tweeters can get expensive.

Good speakers can tolerate fair amounts of clipping without frying their tweeters. 

You already have two of the finest clipping indicators made - your ears. 

Re: Watts per channel meter

Reply #11 –
Quote
...to try and save my speakers from damage from any clipping distortion that could possibly arise from the power amp during musical peaks. Blown tweeters can get expensive.
Tweeter damage due to clipping turns out to be mostly a myth...

If you are actually blowing speakers, the WORST thing you can do is get a bigger amp!   It's better to turn down the volume, and/or get a smaller amp and don't drive it into distortion, or get tweeters/speakers rated for higher power!  ;)

If you've got a 100W amp and you turn it up into clipping, yes you will generate some high-frequency harmonics and it's safer to keep it below clipping.   But, if you replace that 100W amp with a 200W amp and crank it up to just-below clipping, you're sending more power to your speakers and that probably means more power to the tweeter too.

And while clipping generates harmonics, the lower frequencies are usually dominating and some of the original musical  high-frequency information is clipped/eliminated.   There is a limit to how much (relative) power exists in those harmonics compared to the low frequency content that's causing the clipping.   ...If you've ever played around with an audio editor to create a badly clipped file, it doesn't sound like you've boosted the high end.  

If you crank your amp into severe distortion you can increase it's average  output beyond what your speakers can handle.   The increased power level is more likely to damage the speaker than the clipping-generated harmonics.       ...Normal music typically has a 10:1 peak-to-average ratio.    When you push the amp into clipping, the average level increases even though the peak level can't increase.   

Higher average  power such as continuous test-tones or highly distorted program material is likely to damage the speaker...   i.e.   You could probably blow the tweeter in a 100W speaker with a 20W high-frequency continuous test tone.

And, power ratings for consumer speakers are often "optimistic".



   

Re: Watts per channel meter

Reply #12 –
Quote from: RoyM111 on
And there are a lot 'Clipping Indicator' links to build your own device in Google.

I inpected the schematics for several dozen of them, and find that they were all fraudulently titled. They are output indicators, not clipping indicators and are based on the false presumptions that:

(1) A power amp will clip when its output reaches a certain, easily estimated fixed voltage.

(2) A power amp will not clip until its output reaches a  certain, easily estimated voltage that is a fixed fraction of its power supply voltage.

With low impedance and reactive loads, these assumptions are often false.

That all said, I agree that amplifier clipping phobia (as opposed to actual measured clipping) is often part of a fraudulent sales pitch to sell a more powerful amplifier. 

Re: Watts per channel meter

Reply #13 –
While their engineering may be poor, I would reserve the word 'fraud' for audiophile products that are true fakes.
Kevin Graf :: aka Speedskater

Re: Watts per channel meter

Reply #14 –
Quote from: RoyM111 on
The reason I posted this question about the external meters in the first place is to get a few ideas to try and save my speakers from damage from any clipping distortion that could possibly arise from the power amp during musical peaks. Blown tweeters can get expensive.
Then you should have stated this initially. For that scenario, meters are useless compared to your ears and common sense.
Loudspeaker manufacturer

Re: Watts per channel meter

Reply #15 –
Quote from: DVDdoug on
If you've got a 100W amp and you turn it up into clipping, yes you will generate some high-frequency harmonics and it's safer to keep it below clipping.  But, if you replace that 100W amp with a 200W amp and crank it up to just-below clipping, you're sending more power to your speakers and that probably means more power to the tweeter too.

But if you replace that 100W amp with a 200W amp, and play it at the same level, you're keeping it out of clipping, because you have more headroom.

Not that I'd want to be in a normal-sized room with a set of speakers receiving a full 100W for very long, mind.

Re: Watts per channel meter

Reply #16 –
Quote
But if you replace that 100W amp with a 200W amp, and play it at the same level, you're keeping it out of clipping, because you have more headroom.
Exactly what  I said...   I said "below clipping", but putting-out more power and possibly more power to the tweeter.

Quote
Not that I'd want to be in a normal-sized room with a set of speakers receiving a full 100W for very long, mind.
And, if you've got a "clipping probem", 3dB more "headroom" (twice the power) is probably not enough...   If you've got a 10W amplifier that's audibly clipping (and possibly damaging your tweeter) you might need a 40W or 50W amp.

Re: Watts per channel meter

Reply #17 –
Quote from: KozmoNaut on
But if you replace that 100W amp with a 200W amp, and play it at the same level, you're keeping it out of clipping, because you have more headroom.

Replacing a 100 watt amp with a 200 watt amp gives you only 3 dB more headroom. If the clipping is audible or capable of damaging tweeters, you'll probably need a whole lot more added headroom than just 3 dB.

Re: Watts per channel meter

Reply #18 –
That certainly depends on how much you're actually clipping the signal, but yeah. 3dB of headroom is not a lot.

Re: Watts per channel meter

Reply #19 –
Quote from: KozmoNaut on
That certainly depends on how much you're actually clipping the signal, but yeah. 3dB of headroom is not a lot.
I've spent enough time on audiophile forums to have seen this little scam be played out with real people..

Very few audiophiles know what sort of power levels they operate their system at, and as it is with many things audiophile, ignorance presents an opportunity for people to play expert at other people's expense.

The opening gambit from the pseudo-expert is something like "Did you know that you are risking irreversible damage to your tweeters by using that POS amplifier (or receiver) that you are using now?

With his foot inside the door, the pseudo expert embroiders his scare story around the myth that clipping always creates excessive high frequency sounds that always damage tweeters.

Fact of the matter is that almost no audiophiles know the actual power levels they operate their systems at. Rather than admit their ignorance, they cave in to the scare story by the pseudo expert and do something they probably wanted to do anyway, which is buy a more expensive and powerful amplifier, and obtain the bragging rights that come with it.

There is a relative of this scare story that is based on the idea that cheap cables often damage amplifiers and other audio gear with poorly fitting connectors.

There are no doubt others...
 

Re: Watts per channel meter

Reply #20 –
If more amplifiers came with at least semi-accurate power meters, I think that would surprise a lot of people.

When I play properly loud on my old Akai amp, it barely hits 10W* on the meters, and that is full-on "my neighbors are not going to like this" loud.

*I know that's not the peak power, but still.

Re: Watts per channel meter

Reply #21 –
@Arny:
Like anything from this useless and unwelcome idiot or his sock puppets:
http://www.avsforum.com/forum/members/7570690-vaughan-odendaal.html#/enter

Re: Watts per channel meter

Reply #22 –
Quote from: KozmoNaut on
If more amplifiers came with at least semi-accurate power meters, I think that would surprise a lot of people.

A good clipping meter is a >90% solution, while a level meter can range from being somewhat useful to totally misleading.

Many level meters are just lightly-damped analog meters which do very poorly when it comes to responding to short peaks that are often found in music.

Pro audio gear  often has clipping indicators and possibly also lights indicating the presence of fairly minimal amount of signal. As has been pointed out some brands have true clipping indicators and accurate peak-responding level indicators. Many Crown amplifiers are  good examples of this.  If the clipping indicator is built into the power amp, as QSC often does, the incremental parts count and cost can be nearly vanishing, but even very small amounts of clipping can be indicated. Other brands may do as well if not better, but these are the brands I have the most hands-on experience with.

In contrast consumer gear with useful clipping indicators are pretty much like hen's teeth. I think this is because consumer power amps are mostly sized by guess and by golly and what there is a ton of in the store room. In contrast a high percentage of pro audio gear is actually chosen by technical folks who use tend to use measurements and specifications to configure systems.


Quote
When I play properly loud on my old Akai amp, it barely hits 10W* on the meters, and that is full-on "my neighbors are not going to like this" loud.

*I know that's not the peak power, but still.

If we are talking plain-vanilla analog electro-mechanical meters, well something may be better than nothing.

Re: Watts per channel meter

Reply #23 –
Quote from: Arnold B. Krueger on
A good clipping meter is a >90% solution, while a level meter can range from being somewhat useful to totally misleading.

Of course the proper modern solution would be LED clipping indicators with instant response, rather than damped analog meters.

But as you said, finding (modern) consumer gear with actually useful indicators seems to be completely impossible. And I certainly didn't buy the amp for the precision of the meters, I just like to watch the needles dance to the music  ;)

Re: Watts per channel meter

Reply #24 –
Maybe a workaround to arrive at the wattage:

If you know the efficency of your speakers, and you have a dB meter, you can measure how loud they play (in 1m distance for example), and then deduct how many watts are needed for this. Be aware measuring two speakers at the same time will result in +3dB, so just subtract that from the dB meter output.

I have an older Sony amp (http://i.imgur.com/dohjpEU.jpg) and found this method to come pretty close to what the VU meters show.
Blubb