The nitty gritty of watts and amps

[AsSiMiLaTeD]

This may not be the best place to post this, but we appear to have some intelligent people in here, so I'll give it a shot. This gets a little involved, but interesting (at least to me).

OK, so we know more watts is usually better, but not necessarily all the time. From the other post I've got going on amps, we know that more amps is better also. We know how power (watts) is measured, by multiplying the voltage by the current (amps): P = V*A right????

We also know that 'not all watts are created equal', and that more amps is better on a receiver. This leads me to 2 questions:

1. Assuming that we're all living in the U.S., the standard for voltage is something like 120V right? Which means that every receiver is running with a voltage of 120 right? So the only thing that should be the determining factor in power (watts) is current, right??? (We'll leave ohms out of the equation becuase they're a constant in this little experiment) So how can two receivers be rated at the same wattage if they're running the same voltage but different current??? Say I've got a POS Aiwa rated at 200WPC and my H/K rated at 100WPC. If they're running at the same voltage, which I assume they are, how can the H/K with twice the amps be rated at only half the volts (and have 100 times the sound by they way)??? What am I missing here??? Isn't the method for calculating power ratings standardized at this point by the FCC??? Maybe Not??? Is it really in just in how they word their ratings???

2. I've heard that you have to double the power (watts) to get an audible increase in sound - that's from this website. While I don't deny that, I am currently operating under the assumption that that more watts is better (assuming the same 'quality' of watts). For example, if you had two amps, let's say two Adcoms, one rated at 100 WPC and one rated at 150 WPC, the second would produce a better sound right (assuming all other factors constant)? While it may not be louder, I would think that it would just be a little better overall, maybe with imaging and sounstage??? I've not been able to test this theory, just curious about feedback from anyone.

OK, this has gone on long enough, that is all...

[Airplay355]

1. because of the way manufactures measure watts. the POS aiwa is said to have 100 watts/channel, or in ur case 200 but they will but in little tricks that the average joe wont pay attention to. like 100 watts/channel from 100hz to 1khz. by POS aiwa receiver is rated in that way. there isnt a standardized way of ratting watts, if there was then all those boom boxes that say 520 watts!!!! wouldnt sell.

2. the amp with 150 wpc would give u more headroom, and that would mean less stress on the amp at the same volume.

[VR3]

Voltage isn't quite THAT easy.......................

Voltage ranges from the preouts, inputs, low voltage ins and outs, high voltage, etc etc etc etc etc


Airplay, that Aiwa probally pumps out 5 watts continuous..............maybe more?

[Polkfan]

:) :) :)

[Airplay355]

it was enough to power two rti150s and not completely die lol never could watch a movie in surround sound with that receiver lol oh well, guess thats y its not hooked up right now.....POS

[jdhdiggs]

The wattage numbers on recievers and amps is generally RMS and not peak. The aiwa 100W/channel might peak at 102W, where most quality amps you'll see things like 6dB headroom or such. For a 100W amp with 6dB headroom, you'll have peak wattage capacity of 400W per channel instead of the 102W from the POS reciever.

Also, the source tries to act as a voltage source to the speaker so whether the speaker is 1 ohm or 30 ohm, the voltage drop across will be the same, the amps will be different (I=V/R) Therefore it is not the voltage that limits the power, but the ability to provide amperage that causes the amp to clip.

You can build circuits that build voltage above the source fairly easily, on thisng you can't do is produce more power than the wall can provide: Typically 120V and 20Amps: 2400kW If you go look at some of the high end amps, they don't go over this value for all an all channels drivin rating without special notes (dual 20 amp supplies on seperate circuits or 30amp lines) those notes mean non-standard wiring of your house.

As for rating watts, all you have to do is demonstrate that each channel can produce the 200W, not necessarily at the same time or at all frequencies.

Hence, 200W/Channel reciever is typically nowhere near the power of 100W/channel, all channells driven, 10hz-100khz, 6dB dynamic headroom.

Well, I seem to have missed answering your question, but I hope you find the info usefull. So here goes:

1). Yes
2). Headroom is your friend

[Frank Z]

After my first tube amp fiasco I was researching amplifier output ratings and found out that amplifier output is measured at 1khz. If memory serves, this a FCC/FTC requirement. I'll try to dig up the exact reference if anyone wants it.

[PolkWannabie]

jdhdiggs,

6dB of headroom ? ...

I must be living in the wrong world ... Whose have you seen that have specs like that ?

[Frank Z]

Found it! This is copied from The federal trade Commissions Website and is part of a document titled "
Power Output Claims for Amplifiers Utilized in Home Entertainment Products." The document number is 39 FR 15387.


§ 432.3 Standard test conditions.
For purposes of performing the tests
necessary to make the disclosures required
under § 432.2 of this part:
(a) The power line voltage shall be
120 volts AC (230 volts when the equipment
is made for foreign sale or use,
unless a different nameplate rating is
permanently affixed to the product by
the manufacturer in which event the
latter figure would control), RMS,
using a sinusoidal wave containing less
than 2 percent total harmonic content.
In the case of equipment designed for
battery operation only, tests shall be
made with the battery power supply for
which the particular equipment is designed
and such test voltage must be
disclosed under the required disclosures
of § 432.2 of this part. If capable of
both AC and DC battery operation,
testing shall be with AC line operation;
(b) The AC power line frequency for
domestic equipment shall be 60 Hz and
50 Hz for equipment made for foreign
sale or use;
(c) The amplifier shall be
preconditioned by simultaneously operating
all channels at one-eighth of
rated power output for one hour using
a sinusoidal wave at a frequency of
1,000 Hz; provided, however, that for amplifiers
utilized as a component in a
self-powered subwoofer system, the sinusoidal
wave used as a preconditioning
signal may be any frequency
within the amplifier’s intended operating
bandwidth that will allow the
amplifier to be driven to one-eighth of
rated power for one hour;
(d) The preconditioning and testing
shall be in still air and an ambient
temperature of at least 77 °F (25 °C);
(e) Rated power shall be obtainable
at all frequencies within the rated
power band without exceeding the
rated maximum percentage of total
harmonic distortion after input signals
at said frequencies have been continuously
applied at full rated power for
not less than five (5) minutes at the
amplifier’s auxiliary input, or if not
provided, at the phono input.
(f) At all times during warm-up and
testing, tone loudness-contour and
other controls shall be preset for the
flattest response.
[39 FR 15387, May 3, 1974, as amended at 65
FR 81240, Dec. 22, 2000]

What a mouthfull!!

[jdhdiggs]

Well Done Frank! :D

Essentially it looks like you need to write the recievers at (100WX6) is really a 12.5 W/channel, all driven with maybe 3dB of headroom.

Granted this is the extreme low side of "twisting the ratings" but those 700W recievers don't look so impressive now...

[Airplay355]

neither do the 100wpc sony hTIB's

[PolkWannabie]

The weak point of receivers has always been the amplifier section. How could it be otherwise without making the box 18" tall.

[weavercr]

"6dB of headroom ? ...

I must be living in the wrong world ... Whose have you seen that have specs like that ?" by Polkwannibe

I do not know of any current manufactered receivers but in the late 80's both Proton and NAD used to make receivers and amps with 6db headroom. Both dropped this because of cost.

[jdhdiggs]

Originally posted by PolkWannabie
jdhdiggs,

6dB of headroom ? ...

I must be living in the wrong world ... Whose have you seen that have specs like that ?

to add to weaver: I have seen it on several seperate amps and that was my point. Generally amp rating include all of that information where recievers don't.

[PolkWannabie]

I wasn't questioning the fact of whether or not most amps list this statistic, only which one(s) list 6+dB of headroom as a specification.

The specs for even most of the Class A stuff usually says something like >1.5dB, which could of course mean almost anything.

Random examples ...

http://www.parasound.com/products/amplifiers/hca1500aspecs.html

http://www.parasound.com/halonew/A21details.asp

http://www.adcom.com/specifications.htm

http://www.bkcomp.com/pdf/Ref_200_3_2_1_manual.pdf

http://www.nadelectronics.com/hifi_amplifiers/C272_framset.htm

Interestingly enough manufacturers like Krell, Lexicon, Levinson etc. usually don't even list this statistic at all.

[steveinaz]

6dB of headroom would be incredible; I've never seen such an amp in my 32 years of being an audio-geek. Talk about "reserve" power..sheesh..

[weavercr]

Steveinaz

the NAD 2100 amp, I used to own one 60 watts, 6db,
here is a link to the specs bridged mode was 100 watts with 7db headroom.

nad 2100 power amp (http://207.228.230.231/info/NAD_2100.pdf)


the nad 2200 amp was 100 watts 6db,
bridged was 400 watts 5 db headroom.



NAD 2200 amp (http://207.228.230.231/info/NAD_2200.pdf)

and a receiver with 100w wiht 5.7 db headroom.

NAD 7400 receiver (http://207.228.230.231/info/NAD_7400.pdf)

[PolkWannabie]

Hmmm ... That's what some would call fuzzy math ...

[Tour2ma]

Originally posted by Polkmaniac
1. Assuming that we're all living in the U.S., the standard for voltage is something like 120V right? Which means that every receiver is running with a voltage of 120 right? So the only thing that should be the determining factor in power (watts) is current, right??? (We'll leave ohms out of the equation becuase they're a constant in this little experiment) So how can two receivers be rated at the same wattage if they're running the same voltage but different current??? This is an apples and oranges scenario. The AC voltage of the power supplied to the amp does not set the DC voltage differential the amp can produce at its speaker terminals.

Originally posted by Polkmaniac
Say I've got a POS Aiwa rated at 200WPC and my H/K rated at 100WPC... how can the H/K with twice the amps be rated at only half the volts (and have 100 times the sound by they way)??? What am I missing here??? Isn't the method for calculating power ratings standardized at this point by the FCC??? Maybe Not??? Is it really in just in how they word their ratings??? As Frank posted the FTC has a standard, but I believe it's for 2 ch with a rule for "multi" channel being readied. You can comply and still quote other measurements.
Power output (watts) is most often stated as RMS (root mean square) output voltage times the resistance applied to the amplifiers output. HCC (High Current capacity) is generally reported as peak to peak.
Even the NAD's weavercr posted switch to the "IHF" (Institute of High Fidelity) standard for their headroom calc's. This is an old standard the audio industry developed themselves in part to forstall FTC regulation.
You also asked about sound quality. Obviously design, component and build quality are all in play.

[Kpt_Krunch]

Just to throw in my 2 cents (literally) on amps - I have an HK520 rated at 75 WPC all channels driven (5) and 85 WPC two channel driven. Sounds unimpressive doesn't it? The HK520 also has a High Current Capability (HCC) rating of +/- 45 amps. When I demo'd this AVR vs. others (Sony, Pioneer (Not Elite), Yamaha (this was close though) ) and a few others I can't recall now, well it wasn't even close.

And just to speak 'english', the difference at reference levels is not how 'loud' it is, but how it sounds. All the above mentioned receivers could not get close to the HK520 before audible distortion set in. The HK played much louder then all of them save the Yammy (the Yammy still wasn't up to par with the HK, but it was a lot closer then the other receivers) before distortion was noticable.

This was a few years ago, and I was comparing price points. I know Pioneer Elite, Denon's (which were not sold where I demo'd) and other companies make receivers that are much better than the H/K, but I find for the price range of the 520 this was the best receiver out there. It was the amp difference, not the 'watts'.

I guess the best way to say summarize this is they are called "Amplifiers', not "Wattafiers". I don't even look at watts anymore, and if I can't find an amp rating on an AVR, I don't even waste my time listening, as it isn't worth it.

[mantis]

This is one reason I say forget about the spec's to a point.They don't tell the whole story and most of the time lie there face off.

Sound quality has nothing to do with spec's.You can read about juicy spec's and the gear can sound like shit,why????Because most companies love to play"the numbers game".As some of you realized,they don't always tell the whole story like rating one channel driven at 1k......all channels driven from 20 to 20,and how about current,this amp has 75 amps per chanel,then you look at a receiver with the same watt rating and only has 7.5 amps per channel...........good shit huh

Spec's are Important to the level that If you have hard to drive speakers like 6 or 4 ohms with a low 89 or lower db rating,then making sure the amp has the nessary amount of current and is stable driving the load.

massive power rated amps don't aqlways sound better.I have heard many 60 watt to 100 watt rated amps sound so much better then 250 watt rated amps......and so on and so on.

I say listen with your ears,after you figure out that the amp can safely drive your given speakers,it's only a matter of time that you figure out what amp/pre/receiver sounds best.

Such a rough world out there...........Bastards!!


Dan

[PolkWannabie]

Figures don't lie, but liars sure can figure.

[jdhdiggs]

Originally posted by steveinaz
6dB of headroom would be incredible; I've never seen such an amp in my 32 years of being an audio-geek. Talk about "reserve" power..sheesh..

I saw it a couple times on some amps while doing research on them. The 6dB's are out there, but really rare...

[PolkWannabie]

NAD was known for stretching their stats in this area using some sort of snake oil calculation that was recognized by no one but their own marketing staff ...

[gidrah]

I thought they were known for under rating their continuous power rating.

Mantis is right. Specs can get you into the ballpark. Specs can also impede you from melting something. Unfortunately, they can also give a drunken member a sense of over confidence. Did I ever tell you how I blew a mid/woof in a pair of 10Bs (200 watt?) when comparing them to a pair of vintage 30 watt speakers?

[PolkWannabie]

Don't get me wrong. I like NAD gear, but to believe any amplifier has 6dB of headroom I'd have to see it on a bench.

Others who have taken the trouble with the appropriate test equipment could not validate the claims AFAIK and there have been numerous threads in the past regarding this which is one of the reasons why NAD has toned down some of those claims on their more recent products.

After all we don't really believe that they either forgot how to make amps with this much headroom or that they no longer thought it was a good idea, do we ?

As far as melting speakers goes, one can trash almost any speaker using almost any amp. Just turn it all the way up and leave it there and eventually you'll find a movie or music passage that will do the trick.

[gatemplin]

I'm confused. Say an amp has 100W per with 6 dB headroom. Doesn't that mean it really has 400W?

[jdhdiggs]

No, it would mean that it could sustain 100W of power into the speaker, but have temporary bursts of up to 400W without clipping if I am recalling everything correctly.

[Tour2ma]

Ed Zachery... headroom is short-term power for music transients.

Headroom is just not a term that you hear much anymore. Once it was "the" stat for amps. For a while it seemed that everybody's amp had at least 3 dB of it. NAD, Adcom and Proton all beat the headroom drum loud and long.

But in parallel with the headroom craze watts and current just got so damn cheap that headroom just wasn't an issue. I mean my poor old M-1.5t only had ~1.2 dB's of it. Ultimately raw power won out...

As for NAD, as I said above, they jump shifted to the old ihf standard for their headroom rating. The ihf rating system was ultimately insufficient to stave off FTC rules as it was too easily manipulated.

That said, having once again heard NAD amps at Russ', I was reminded how much I liked them back when headroom was cool.

Stat's have their place and are quite useful in narrowing the field.

As for trashing a speaker, hell you don't even need an amp. Just wire it to a wall socket...

[Dennis Gardner]

As for trashing a speaker, hell you don't even need an amp. Just wire it to a wall socket...
I've seen this done with raw drivers in an auto stereo store.
That 55-60hz hum is quite something to see on some of those
15-18" models that can handle the burst, then blow the cone out of the lesser speakers 20 feet into the air.

Talk about extreme marketing!

:D

DG

[Ceruleance]

hmm so if the wall socket is 120v and your driver is two 8 ohm voice coils wired in series, for 16 ohms total, you would get 7.5A current pull and would be throwing 900 watts at the driver?

Am i doing this right? 900 watts isn't unheard of for power handling, as long as the coils really are 8 ohms. If you have dual 2 ohm coils you are looking at like 3,600 watts..

someone confirm to me that I passed high school physics and it wasn't a fluke

[jdhdiggs]

The VC might take that many watts if there was a load on the woofer (enclosure). Without one, the speaker would throttle itsef mechanically. Also, ROT from the infinate baffle guys, if you don't have an enclosure, de rate your speaker 3X. to handle 900W, you would need at 2700W power handling. Beyond that, your math is right.

Also, FYI: ~742 Watts = 1 Horse power IIRC

[Tour2ma]

WAAAAAAAAAaaaaaaaaa...

My Sunfire is pushin' nearly 3 hp!!! :D

[Ceruleance]

Originally posted by Tour2ma
WAAAAAAAAAaaaaaaaaa...

My Sunfire is pushin' nearly 3 hp!!! :D

you could mow your lawn with that thing!

[John K.]

The form of Ohm's law defining power can be stated as PM did in his question: P=VxA(power in watts equals volts times current in amps). Although power from the wall socket is in the area of 120V, it should be kept in mind that the amplifier doesn't use it at this voltage. The transformer in the power supply section of the amp or receiver steps down the voltage typically by about 4 to 1, which then is rectified to DC and is cleaned up and briefly stored by the filter capacitors. The amp section itself then uses the power at a voltage of about 30-35V.

When playing at a comfortably loud listening level speakers use about 1-2 watts. On brief peaks 100 watts or more can be used. If for example some extreme peak called for 150 watts, the application of Ohm's law would be 150 watts equals say 30 volts times the required amperage, which would call for a 5 amp capability.

[motocrossluke]

all amps and recievers are not created equal even though some of the ratings are the same.Current is the main factor. here is a good example. if you take 8 AA batteries and hook them in series, you will have a total of 12 volts DC. 8 x 1.5 volts,the exact same voltage as your car battery . Does that mean that you could start your car with the 8 double AA batteries.? Of course not. These 8 batteries are not able to supply the current needed to turn such a heavy load that a car battery is able to supply. Wattage measurments alone do not tell us how much current an amplifier can produce

[bknauss]

But you know currenty from just about every power spec out there since they quote the resistance used. Now if you're reffering to how much current a power supply can deliver (which ultimately becomes the biggest factor in most AVRs and their total average power), that's a completely different story. A company might quote X watts per channel, but they're only measuring 1 or 2 channels. When you drive all channels, the average power out of each channel can drop dramatically based on the power supply.

[AsSiMiLaTeD]

Holy shit this thread is like 2 years old!!!

How do we keep digging up these old threads?

[cheddar]

People keep telling newbies to use the search function to dig up stuff on amp separates etc...

[steveinaz]

I think when you talk in terms of "more power" being better, we're talking about being able to reproduce music in lifelike "scale" without the amplifier peaking out/clipping. Scale is every bit as important as any other specification as it is related to the term "fidelity." You have to be able to recreate the musicians scale to realistic levels to be true to (fidelity) the performance in dynamics.

Of course all of this dependant on room size, speaker efficiency, etc...

[sickicw]

I think when you talk in terms of "more power" being better, we're talking about being able to reproduce music in lifelike "scale" without the amplifier peaking out/clipping. Scale is every bit as important as any other specification as it is related to the term "fidelity." You have to be able to recreate the musicians scale to realistic levels to be true to (fidelity) the performance in dynamics.

Of course all of this dependant on room size, speaker efficiency, etc...


yea, I think that is something that most people don't understand. I feel that dynamic range is by far the most important attibute that defines what makes music sound good. In fact, I would prefer listining to mp3s on a good system with plenty of power than i would a sacd on a system that limits the dynamic range. Of course, most people that have sacds also have a decent system, so this might not be a good example.

[aaharvel]

Wattage never sold me on my amp. It was headroom capability and +/-100 current. Put those specs on a 10 watt tube amp and my speakers would sing.

[bikezappa]

all amps and recievers are not created equal even though some of the ratings are the same.Current is the main factor. here is a good example. if you take 8 AA batteries and hook them in series, you will have a total of 12 volts DC. 8 x 1.5 volts,the exact same voltage as your car battery . Does that mean that you could start your car with the 8 double AA batteries.? Of course not. These 8 batteries are not able to supply the current needed to turn such a heavy load that a car battery is able to supply. Wattage measurments alone do not tell us how much current an amplifier can produce

This topic was very interesting in my EE class 40 years ago. All batteries have an internal resistance. The D cell battery has more internal resistance than a car battery. That's why you can measure 1.5 volts from a battery that is dead and can't light the flash light. It's internal resistance has increased over time due to the nature of the chemical reaction going in the battery.

Let me expalin it another way. A D cell has 1.5 volts. It also has an internal reisitance called Ri. From ohms law Voltage = current X Resistance or

E=IRi
or
I=E/Ri

When you short out a D cell battery, that is connect a wire directly from the + terminal to the - the amount of current is 1.5 volts divided by the internal resistance. If the internal resistance is 0.1 ohms then you will have 15 amps going thought the wire. This makes for a very hot battery very quickly. It can explode. The internal resistance of the battery is not constant and will increase with time. Also the internal resistance will increase with heat which will reduce the current with time of a shorted out battery. By careful if you try this D cell battery experiment at home kiddies.

To summarize, the important factor in power supplies is the internal resistance, lower is better. They all have the same 30 or so volts as some else has already noted.

A side note, the most effecent power transfer from amplifier to speakers is when the internal resistance of the amplifier = the resistance of the speaker.

Does every one get it?

Ohms law, E=IR and watts W=IE are two very powerful tools used to understand all our electrical equipment. If you use a little algerbra and substitue you can also make W=IIE or W=EE/R. Have fun.

[LuSh]

You're wasting your time, as soon as Japan took over the consumer electronics industry and basically used numbers to market products it was game over. I find the HK number very funny indeed. Using ohm's law caculate what 45 "AMPS" of current would be outputted to an 8ohm speaker...you're looking at over 16,000 watts to the speaker...The HK spec is horse s***. As is much of the industry when it comes to numbers. Ever wonder why a data projector can be spec'd higher in contrast then a $10k Sim2?

I can't stress enough if you're passionate about Audio stick with local dealers and help support the industry. The math is there only to fool you trying to entice you to buy based on price and spec'd performance allowing large national retail chains to retail niche products.

[bikezappa]

Lush

That's correct, and your amp would need to output about 600 volts to make 35 amps into an 8 ohm speaker.

Proper math doesn't lie. It's the data that the manufactures give that is a lie.

Do the test yourself Polkies. Measure the RMS voltage to you speakers to determine the Watts to the speaker.

W=IE

or substituting in ohms law I=E/R, E being the voltage to the speakers and R being the speaker resistance and I being the amps to the speakers

we get

W=EE/R

Do the experiment to see how loud you can take it and then measure that voltage. You will be surprised how few Watts you are using.

[dudeinaroom]

120v is the power supplied to the transformer, not for amptilication. The transformer then puts out a certain amount of voltage. this is the rectified(changed to dc) and then smoothed by capacitors(which also hold reserve energy for peaks) so now you have some thing like +35, common/ground, and -35 volts which feeds the amplifier circuit. which might be what the haron would use. but in the cheap aiwa it might be a stetup with +/- 12 volts or even just 12 volt and ground. an amp cannot put out more voltage/current than it is fed and will waste energy as the by product know as heat. so thats part of the reason why they don't have the same out-put and antoher part of it is the design of the amlifer ciruit which is a whole other can of worms

Later polkies