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[Bob Lee (QSC)]

I drop in at GC and other stores now and then but don't let on that I work for QSC. It's interesting to hear salesmen's myths and learn about the misinformation I'm so often up against.

So, were they real double-blind tests? Many people don't know what the correct methodology is. The PLX and PowerLight amps will really reproduce faithfully what you put into them, up until the point of clipping, so maybe what really displeased you was the input signal.

[Iain_Macdonald]

Mel,

Everything that JR says plus: the load[speaker] needs to be taken in to consideration. Studio speakers are just as bad as many PA products for presenting 'impossible' loads. I do agree with you that some amps sound better than others. Just try one of the large Chord amps and hear the difference it makes. But I do sound a note of caution. The human hearing system is adaptive, and it can adapt very quickly to what you hear. Any subsequent listening in the very short term can be colored by your immediate past experience. That is why double blind test methodology is preferred. I would also agree with your point on the degradation of the signal chain. The system is only as good as the weakest link. So many products are compromised, it's often hard to get a true picture of what's happening. This is especially true of digital products. Though the Lake Contour is a shining example of a clearly better product.

But I would say that we need to be pragmatists, however unpalatable that may be to you.

Iain.

[Tim Duffin]

Bob...

I can't believe this sentence was actually written by an amplifier engineer:

"The PLX and PowerLight amps will really reproduce faithfully what you put into them, up until the point of clipping, so maybe what really displeased you was the input signal."


Whatever happened to frequency response, total harmonic distortion, intermodulation distortion, crossover distortion, etc?  No audio device capable of reproducting sound has 0 distortion.  Adding qualifiers to statements like "only when used properly" or "out of clipping" says nothing about what happens to an amp when it is ACTUALLY USED.  I too could design an amp that has .000000001% THD if it is only required to source 1/400th of its total power.  What really matters is what an amplifier does when it is pushed to its absolute limits.  For instance, if it is a BASS amp-- it should be run at 100% RMS and 100% duty cycle inside a rack with sagging electrical mains (gotta factor in the 300KW lighting rig on the same service) in 100 degree sunlight in a black amp rack with heavily compressed 50Hz sine waves for 8 hours.  

Then we will know what an amp does after its not on the testbench at the manufacturer under the absolute most favorable conditions that the manufacturer could possibly create.  

T

[Don Boomer]

Gee ... I thought he said "faithfully"  ... not "perfect"

See the qualifier here is "up to the point of clipping".  That usually means less than 10% of it's rated power.  If you run an amp with proper headroom you're just not gonna "hear" the amp.   What you "hear" is how the amp handles overloads, how it recovers, etc.   ABX tests time after time prove that out ... and that's under critical listening conditions.  Live sound rarely gets close.

How the amp is actually used I guess depends on if the guy knows how to use it

[Doug Fowler]

Quote:

Whatever happened to frequency response, total harmonic distortion, intermodulation distortion, crossover distortion, etc? No audio device capable of reproducting sound has 0 distortion. Adding qualifiers to statements like "only when used properly" or "out of clipping" says nothing about what happens to an amp when it is ACTUALLY USED. I too could design an amp that has .000000001% THD if it is only required to source 1/400th of its total power. What really matters is what an amplifier does when it is pushed to its absolute limits. For instance, if it is a BASS amp-- it should be run at 100% RMS and 100% duty cycle inside a rack with sagging electrical mains (gotta factor in the 300KW lighting rig on the same service) in 100 degree sunlight in a black amp rack with heavily compressed 50Hz sine waves for 8 hours.

All this from a guy who thinks MacroTechs suck and who doesn't meter his power at gigs.

The chance of you outliving this stigma are about as slim as Miffe getting away from that photo JJJ likes to share.  Me, I think it's a damn fine photo and it sort of reminds me of my senior photo in the old high school yearbook.

But that was a long time ago, of course.

[Tim Padrick]

I've not comparison tested any QSC amps, but I have tested some others.  The source was a Linn Karik CD player.  The two test loads were Acoustic Energy AE1s, and a bench load monitored with Grado 100's.  The results between amps were the same on both loads.  The results were:

Linn Klout

Arcam P90

Many steps below those:

Crown K1 (tested in both stereo and bridged).

Several steps below that:

Crown K2.

Very close behind were the Crown Micro 1200 and CE4000.

A step or two behind those was the Mackie 1400.


Of course the first two are of such low power and duty cycle capacility that they are useful only for home hi-fi and perhaps studio monitoring purposes.  Ignoring them, the K1 was quite a bit better than the others.  (I also compared the K1 to a K2 in a bass rig, and again the K1 sounded a lot better when not driven to clipping.)  The K1 of course is only enough power for horns and maybe wedges that are very efficient or not driven very loud (unless the K1 is bridged - in which mode it still sounds better than the others even when driven to its limits).

[John Roberts {JR}]

Tim Duffin wrote on Tue, 21 November 2006 19:38

Bob... I can't believe this sentence was actually written by an amplifier engineer: "The PLX and PowerLight amps will really reproduce faithfully what you put into them, up until the point of clipping, so maybe what really displeased you was the input signal." Whatever happened to frequency response, total harmonic distortion, intermodulation distortion, crossover distortion, etc?  No audio device capable of reproducting sound has 0 distortion.  Adding qualifiers to statements like "only when used properly" or "out of clipping" says nothing about what happens to an amp when it is ACTUALLY USED.  I too could design an amp that has .000000001% THD if it is only required to source 1/400th of its total power.  What really matters is what an amplifier does when it is pushed to its absolute limits.  For instance, if it is a BASS amp-- it should be run at 100% RMS and 100% duty cycle inside a rack with sagging electrical mains (gotta factor in the 300KW lighting rig on the same service) in 100 degree sunlight in a black amp rack with heavily compressed 50Hz sine waves for 8 hours.   Then we will know what an amp does after its not on the testbench at the manufacturer under the absolute most favorable conditions that the manufacturer could possibly create.   T

  For instance, if it is a BASS amp-- it should be run at 100% RMS and 100% duty cycle inside a rack with sagging electrical mains (gotta factor in the 300KW lighting rig on the same service) in 100 degree sunlight in a black amp rack with heavily compressed 50Hz sine waves for 8 hours.  


100% RMS ?? Do you perhaps mean 100% rated power? At which impedance? Which rated power?

100% duty cycle..  OK full on, for all the time...

Inside a rack ? OK.

With sagging electrical mains...  Um.. that could be a problem. A typical amp won't put out full rated power if it doesn't have rated mains voltage available. How an amp will act with or w/o a clip limiter turned on will make a huge difference in that  situation (clipping).

100' sunlight.  100' ambient, with a hot rack apparently...

BTW, how do you compress a 50 Hz sine wave?? If it was already running at full power applying heavy compression will just turn it down??

8 hours... Now that I understand... 480 minutes...

==============
I'm afraid I can't make much sense of your comments. If your point is that amplifiers clip and operate in their nonlinear region when driven hard, I'm inclined to agree.

Your ranting makes any real argument extremely difficult to parse out and therefore it is very easy to dismiss the whole screed. If you have a specific point please make it more clearly.


JR


PS: FWIW I don't know of too many amps that will put out full rated power for 8 hrs continuously.  

[Tim Duffin]

they do suck and so what if I blew a couple amps a couple times

T

[Tim Duffin]

John Roberts  {JR} wrote on Wed, 22 November 2006 02:36

Tim Duffin wrote on Tue, 21 November 2006 19:38 Bob... I can't believe this sentence was actually written by an amplifier engineer: "The PLX and PowerLight amps will really reproduce faithfully what you put into them, up until the point of clipping, so maybe what really displeased you was the input signal." Whatever happened to frequency response, total harmonic distortion, intermodulation distortion, crossover distortion, etc?  No audio device capable of reproducting sound has 0 distortion.  Adding qualifiers to statements like "only when used properly" or "out of clipping" says nothing about what happens to an amp when it is ACTUALLY USED.  I too could design an amp that has .000000001% THD if it is only required to source 1/400th of its total power.  What really matters is what an amplifier does when it is pushed to its absolute limits.  For instance, if it is a BASS amp-- it should be run at 100% RMS and 100% duty cycle inside a rack with sagging electrical mains (gotta factor in the 300KW lighting rig on the same service) in 100 degree sunlight in a black amp rack with heavily compressed 50Hz sine waves for 8 hours.   Then we will know what an amp does after its not on the testbench at the manufacturer under the absolute most favorable conditions that the manufacturer could possibly create.   T   For instance, if it is a BASS amp-- it should be run at 100% RMS and 100% duty cycle inside a rack with sagging electrical mains (gotta factor in the 300KW lighting rig on the same service) in 100 degree sunlight in a black amp rack with heavily compressed 50Hz sine waves for 8 hours.   100% RMS ?? Do you perhaps mean 100% rated power? At which impedance? Which rated power? 100% RMS is what the manufacturer states is the amps RMS--at whichever impedance the manufacturer states GIVES the HIGHEST rated power--and finally the AES standard power rating conventionally used today. (Do I really have to type this, I'm assuming that people reading this have a certain degree of experience in test engineering or at least reading the owners manual) 100% duty cycle..  OK full on, for all the time... Inside a rack ? OK. With sagging electrical mains...  Um.. that could be a problem. A typical amp won't put out full rated power if it doesn't have rated mains voltage available. How an amp will act with or w/o a clip limiter turned on will make a huge difference in that  situation (clipping). Really... I thought that multi rail amplifiers tended to deal with sagging mains more efficiently than dual rail amps.  Sagging mains are a reality-- so why not rate a particular amps performance with that in mind? 100' sunlight.  100' ambient, with a hot rack apparently... BTW, how do you compress a 50 Hz sine wave?? If it was already running at full power applying heavy compression will just turn it down?? Oops, that was a typo-- I was thinking faster than I was typing.  I meant either heavily compressed continuous LF or a 50hz sine wave.  If a sine wave generator is not available, just play some jungle or bass music to test an amps LF performance--not Van Halen. Incidentally, I agree that there aren't any amps that put out their "rated" power after 8 hours-- I want to know what they do put out after 8 hours straight and call that the "I am actually using this amp in a situation which is not in a lab so what does it actually put out" power.  Then, we can compare the "rated" power to the "real" power specs and see which amps live up to their ratings. 8 hours... Now that I understand... 480 minutes... ============== I'm afraid I can't make much sense of your comments. If your point is that amplifiers clip and operate in their nonlinear region when driven hard, I'm inclined to agree. Your ranting makes any real argument extremely difficult to parse out and therefore it is very easy to dismiss the whole screed. If you have a specific point please make it more clearly. JR PS: FWIW I don't know of too many amps that will put out full rated power for 8 hrs continuously.

[Andy Peters]

Doug Fowler wrote on Tue, 21 November 2006 19:15

The chance of you outliving this stigma are about as slim as Miffe getting away from that photo JJJ likes to share.  Me, I think it's a damn fine photo and it sort of reminds me of my senior photo in the old high school yearbook.

Dunno where JJJ is right now, so I'll "help" :

[ProSoundWeb Community]