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Re: B&K Receiver for M80's
Zimm #275104 10/15/09 08:48 PM
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The ghost of the horse asked me to move on...


Panny 3000 PJ, 118" Carada, Denon 3300, PS3, Axiom QS8, PSB 5T, B&W sub, levitating speaker wire
Re: B&K Receiver for M80's
Zimm #275114 10/15/09 09:42 PM
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Not to fear, there are a few of us on the forum that feel the same as you, especially after I experienced such a difference in sound from my 3808 compared to the 3808/A1400 combo. You can never have too much power, even if you only use a little of it once in awhile \:\)


Jason
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Re: B&K Receiver for M80's
Zimm #275134 10/16/09 01:59 AM
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Charles, thanks for showing those test numbers, because the use of the term "clipping" there makes no sense at all. Actual clipping would be evidenced by distortion at least 100 times that 0.016% figure. The test numbers confirm the excellence of your 3300 and indicate that audibly clean output on the order of 140 watts was delivered.

Although the use of "clipping" in that commentary is, again, incomprehensible, I do know the context in which S&V uses the term. It is the point at which THD reaches 0.3%. This is still rather strange usage of the term(inaudibly low distortion would be a more accurate descriptive term at that point), but not nearly to the same extent. Actual clipping shown by flattening of the top of the waveform doesn't occur at any specific THD level, but certainly in all cases would be greatly in excess of 1.0%.


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Re: B&K Receiver for M80's
JohnK #275136 10/16/09 02:29 AM
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I disagree on semantics, but agree on principle.

Clipping by definition is when the peaks of the output waveform don't follow the input. The farther it is pushed the more that is clipped. At some point it become audible, and after that visible on a scope as a flatten (DC) line. It is silly when reviewing an amp to say it has reached maximum usable power when if fails to track the peak by a microvolt, as you said that's completely inaudible. But by the time you can see it on a scope, your tweets are on their way out.

So yeah, the amp was "clipping", but not in the audible sense, and far from the olfactory sense.


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Re: B&K Receiver for M80's
ClubNeon #275162 10/16/09 06:18 AM
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OK, so as soon as there is any distortion, we technically have clipping?? Like say at .001% THD + N I know this is a somewhat exagerated point, but since we can measure to this resolution...

At any rate, from what I have read, waveform distortion does not become audible until somewhere around 1% on normal program material, or .5% with pink noise (Toole I think).

How are the Maximum power ratings on a receiver determined? I presume there is an FCC spec.


Fred

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Re: B&K Receiver for M80's
fredk #275165 10/16/09 07:02 AM
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No, there are many types of distortion. Any time the output signal doesn't completely follow the input it is said to be distorted. It's pretty much impossible to build an analog circuit with active components which does not distort the signal in someway as it passes through. Based on that, as you can see, sheering off the tops of peaks is definitely distortion.

There are two classifications of harmonic distortion. Even-order and odd-order. Clipping causes odd-order harmonics, which sound harsh. But tube amplifiers primarily have even-order, which is almost pleasing to the ear, it causes the sound to seem "warm" or "fat". One can have 5% even-order distortion and still think things sound great.

As John said, the usual way one measures an amp is to drive it until the clipping is contributing 0.3% to the THD. At that point the amp is giving all its truly usable power. Though there are still different measurements here. Some use a 1k sine wave, others broadband (20 to 20k) noise, sometimes one channel driven, sometimes all. The FTC says (not the FCC, the Federal Trade Commission came in to stop the deceptive advertising), all channels driven with broadband noise.


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Re: B&K Receiver for M80's
ClubNeon #275166 10/16/09 09:17 AM
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 Quote:
As John said, the usual way one measures an amp is to drive it until the clipping is contributing 0.3% to the THD.

Maybe I'm being pedantic, but thats not what John said at all, thats what the magazine article implied.

What John wrote was:
 Quote:
Actual clipping shown by flattening of the top of the waveform doesn't occur at any specific THD level, but certainly in all cases would be greatly in excess of 1.0%.


So, is there an accepted 'industry standard', or is this one of those audiophile things that is endlessly debated?

By the way Zimm. I am not implying that you are flogging a dead horse, just asking questions about something I do not quite understand.


Fred

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Re: B&K Receiver for M80's
fredk #275168 10/16/09 09:26 AM
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No Fred, as Chris noted, there's distortion always present apart from actual clipping, which causes much higher THD numbers than "regular" distortion. As I mentioned above, actual clipping(not the rather strange usage of the term which some audio publications adopt)isn't related to a specific distortion number, but rather, occurs when the top of the waveform is flattened("clipped"), as viewed on an oscilloscope. Distortion at this point would be well above 1.0%, not the 0.3% or even 1.0% figure termed "clipping" by some publications.

Yes, blind tests have indicated that on music distortion isn't audible until it passes a threshold in the area of 1%. The more complex the music, the higher the threshold of audibility.

Maximum power ratings for all amplifiers for home use sold in the U.S.(and in practical effect, Canada as well)are governed by Federal Trade Commission regulations found in Title 16, Part 432 . Basically, following a warm-up period, the amplifier must be driven at the full rated power for at least 5 continuous minutes, with the bandwidth and maximum distortion specified. Note that the number of channels to be driven simultaneously isn't specifically set, although the FTC interpretation has been to require at least two. The vast majority of receivers are rated with two channels driven, which is a more realistic measure in real-world home use than an all-channels driven measure adopted by some manufacturers, but which doesn't reflect a realistic scenario outside of the testing lab, with all channels simultaneously operating at full power for 5 minutes continuously.

The irony relating to published official power ratings is that this is the only area in audio which is governed by relatively strict regulations and where we can be confident of getting what's claimed, yet it's an area where many suspect "exaggeration" "inflation", etc. , which no manufacturer would risk. Some of those voicing such suspicions are also the same individuals who have no problem with believing in magical sound properties in various items, even pieces of wire, despite the lack of solid evidence.


-----------------------------------

Enjoy the music, not the equipment.


Re: B&K Receiver for M80's
JohnK #275179 10/16/09 01:52 PM
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So what you're saying, if I understand it, John, is that what we see as the RMS rating is governed by the FTC. So if an amp is rated at 100 WPC, .08% THD, those figures MUST be correct per the FTC--HOWEVER, that would seem to be somewhat arbitrary, because the same receiver might be able to do 120WPC, at, say, 1.2%THD (assuming it doesn't shut down), and likewise might do 80WPC at .007% THD.


I am the Doctor, and THIS... is my SPOON!
Re: B&K Receiver for M80's
Ken.C #275191 10/16/09 04:02 PM
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Yes, the FTC Amplifier Rule is more about truth in labeling than a standardized testing methodology.

Reading the actual rule. It seems that he "warm up" is done with a sinusoidal signal of 1 kHz, at 1/8 the rated power for an hour. Then the 5 minute test starts. Because I've always seen the test listed as 20 to 20k Hz, I assumed that was the requirement, but the only requirement is that the test signal be across the band for which the amplifier is rated.

The reason many read the rule as all channels driven is because of these phrases, "...measured with all associated channels fully driven to rated per channel power...", and, "...only those channels dedicated to the same audio frequency spectrum should be considered associated channels that need be fully driven simultaneously to rated per channel power." The second part meaning you don't have the drive the sub at the same time. But a manufacturer could say that the surround and center are not dedicated to the same audio frequency.


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