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Author Topic: QSC Jumps in with both feet.  (Read 27606 times)

John Roberts {JR}

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Re: QSC Jumps in with both feet.
« Reply #10 on: November 14, 2014, 12:03:46 AM »

I would think a standard test-regardless of its being applicable to a given genre-would allow comparison,  Of course, getting the industry to agree on a standard rating won't happen until audio techs as a whole demand real info and not bragging numbers.  Then adjustments can be made for content that would allow you to know what you needed when upgrade replacement time came around.
As I've said before I am not smart enough to come up with an optimal, widely representative test.  I expect any new metric would be as misunderstood in the marketplace as current metrics. Further any such test would be targeted by amp designers, so the test better be right because that is what you will get in future amps. WHo would try to sell one that doesn't pass the test? That is kind of what happened with the FTC 1/3 power preconditioning test. In their effort to beef up power amps they said they had to be run at 1/3rd power for a significant warm up period "before" measuring the rated output power. If you know anything about amps, hot amps make less power than cool amps. Another fact you may not know if you don't design power amps, 1/3rd power for a class AB power amp is worst case for dissipation and heating up. In class AB and 1/3rd power, the heat sink is dissipating twice as much power as the amp is putting out. So the class AB amps had to revise their power output downward, but new amps using class G or class H (multi PS rail) topology, could dial in the lower rail voltage to run cool as a cucumber at 1/3rd power, whether that was optimal or not for music.     

So any duty cycle test will be targeted by manufacturers (for better or worse) like the FTC preconditioning 1/3rd power.
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Personally, if I read the fine print specs and find a manufacturer is in the habit of overstating things I tend to write them off as a supplier-at least as far as my first or second choice goes.  Where else are they cutting corners?  Give me a quality product with honest specs and I won't try to beat you up on pricing.

I have been around this tree too many times and had to defend the honor of my old employer here many times over the years. One of the nightmare calls for service was a customer with a meter and a dummy load (well named) claiming that their amp doesn't make rated power, plugged into their wimpy garage outlet or extension cord. 

Sorry this is an old subject I have written about for years. If it was simple I would have proposed a test procedure back when Bink did his amp shootout.

JR
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Jeff Bankston

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Re: QSC Jumps in with both feet.
« Reply #11 on: November 14, 2014, 03:57:26 AM »

Perhaps because that is exactly what customers respond to. Nobody got rich understating their product performance.

FWIW QSC was early to the game with less than full duty cycle amps with 2 ohm capability. And everyone followed them down that rabbit hole because the customers embraced it with dollars..

This is probably business as usual.

JR
Are you refering to the old QSC Series 3 amps ? 3350 , 3500 , 3800.
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Steve M Smith

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Re: QSC Jumps in with both feet.
« Reply #12 on: November 14, 2014, 05:43:25 AM »

As far as I'm concerned, there's nothing wrong with using RMS as a measure.  I don't think it's a coincidence that all other measurement methods give you higher numbers and that salesmen prefer higher numbers to low numbers!


Steve.
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Bob Faulkner

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Re: QSC Jumps in with both feet.
« Reply #13 on: November 14, 2014, 07:32:36 AM »

I found it odd the first feature was "modern styling"  The first thing I though to was GX-5 and GX-7 with the DSP.  Appears not to be so.

Out of curiosity it was stated the GX-5/7's are not suitable even for monitors.  They have been my monitor amps for years and never let me down.  Since half of what I thought to be true has be debunked here might as well  start on the other half.  Bob, care to elaborate on the below comment?

My experience with the GX line has been questionable; dependability and power ratings were the issues.  The GX power ratings appear odd when using the amp with either one or two speakers connected to it.  Worked with one amp that stopped producing power (power was on, no one was "home").  The sound quality of the amps always appeared good, and they were light weight.  Though, the amplifiers were not part of my system; they belonged to someone else.

I'm glad your experience with them has been positive.  I use all PLX series amps (12) and have been very pleased.  Unfortunately, my experience with the GX has been marred.




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David Parker

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Re: QSC Jumps in with both feet.
« Reply #14 on: November 14, 2014, 07:38:38 AM »

Perhaps because that is exactly what customers respond to. Nobody got rich understating their product performance.

FWIW QSC was early to the game with less than full duty cycle amps with 2 ohm capability. And everyone followed them down that rabbit hole because the customers embraced it with dollars..

This is probably business as usual.

JR
I remember when QSC came out with their MX1500. It instantly looked like an amp twice as powerful as Peavey's CS800, when in reality, they weren't that far apart. And I remember shortly after that the CS800's 4ohm bridged rating went up to 1200 watts.
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Bob Faulkner

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Re: QSC Jumps in with both feet.
« Reply #15 on: November 14, 2014, 07:39:43 AM »

Bob Faulkner's statement, not mine.

My concern's, regardless of hardware type may just be too old school. Give me the continuous power at a specified load for a specific period of time. Like in my early HAM radio days transmitters and linear amplifiers were rated "key  down" for a specific period of time at a measured output in real watts. As a matter of fact, there was a famous manufacturer who advertised their linear's as key down forever at 2000 watts RF. There ad's featured a skeleton holding down his morse key and the linear still running strong. Give me that and I'll never complain, the very reason I have the faith I do in JBL's drivers.

"CQ Field-day... CQ Field-day..." It's been many years since being around a ham radio (Heathkit specifically!).

You're absolutely correct on the power ratings.


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Ivan Beaver

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Re: QSC Jumps in with both feet.
« Reply #16 on: November 14, 2014, 07:50:46 AM »

I used to be a power amp product manger and will spare you "the only honest man in Dodge" speech (Ivan?) but continuous power is only required for a narrow subset of LF bandpasses of multi-way systems being pounded hard with low bass. Even then there will be some small crest factor, but not much. I know because we were selling continuous duty amps back then and the market rewarded and embraced partial duty cycle power.


JR
I am TOTALLY from your school JR.

I used to be down on the whole "peak power" thing-and continuous was the way it was always done.

However even back in the day there were some brands that would put out the rated power continuously (Peaveys included in the "always meet spec" category ) and others that I never could get to put out rated power.

it was said many years ago by a wise man " What we need is an amp that can put out 100 watts continuous and pass 20dB peaks".  So that would be 100 watts continuous and 10,000 watt peaks.

The real "discussion" at this point (at least as I see it) is how LONG is that peak to be?

5ms, 20ms, 100ms, 500ms?  It make a big difference on the freq being produced and what it will sound like.

Now for sub duty-it is a VERY different thing.  Modern music has a lot of sine wave content-and you need an amp that can produce low freq for often a couple of seconds.

If the amp can't do it-then the level will drop down-sometimes 6dB or more.

As JR knows-making an amp that can produce continuous high level power for a long time is much different than one that can produce it for a couple of ms.

But as you say-the general buying public just wants a high number-no matter whether it is true or accurate or not.  They will just "believe" it is correct--------------

So as the usual answer always it-it depends. 

Having an amp that can produce high level of voltage for short periods of time is fine-AS LONG AS that period of time is long enough for the particular musical content being played at that level.

THAT is where is gets a bit more complicated-and the "general public" doesn't want to think about things like that-they just want a high number at a cheap price.

Real professionals (NOT most of the ones calling themselves professional) will look a bit deeper at the specs and make sure it is correct for the intended usage-but those people are RARE I am sad to say ;(

JR-I feel your pain-------------
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Ivan Beaver
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Ivan Beaver

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Re: QSC Jumps in with both feet.
« Reply #17 on: November 14, 2014, 08:07:16 AM »

And just to add another comment to JRs statements.

I remember "back in the day" there were some amps that were advertised to have a
"Higher dynamic range"-which meant that they could pass peaks that were something like 3dB or more greater than the continuous rating of the amp.

Of course the "rating" they used was the peak rating.

But what this REALLY MEANT was that the amp could not produce the continuous power for very long-which meany it had a wimpy power supply!!!!!!!!!!!!!!!!!

But this was marketed as a FEATURE :0 because people "thought" it could reproduce peaks better.

YEAH-Let's find a way to take a negative and make people "think" that it is better---------

I guess that is why I am not in marketing.

Even though I believe the "impulse/peak" power is the proper way for real amps used in audio-I would like to ALSO see the continuous (at least for 2 or 3 seconds if not 5 minutes) output into a particular load.

But manufacturers don't want to publish that-because unless everybody does so most people will look at the lower number an think that is all they can get out of it.

A clear case of how providing to much information on a data sheet will actually hurt sales.

And you can see this on quite a few products (especially loudspeakers) in which there is very little useful information published-so there is no way a customer can compare it to a product that has more data.  They just hope the customer will "believe" what they are saying-with no proof to back it up.

A simple UNPROCESSED freq response should be the MINIMUM-but that is pretty rare these days.  And many people simply don't care.  I guess partially because they are to stupid to be able to read a simple graph.  Yes I have meet a good number of "professionals in this industry" who cannot read a freq response graph.

Ask them "If the manufacturer says the sensitivity is 100dB, then at freq is it 3dB down?

Blank stares are all you get out of them.  REALLY SAD in my opinion :(  But many manufacturers RELY on this ignorance in order to sell product-and they do a good job of it.

Getting off soap box now before I say something that will get me in trouble -----------

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Ivan Beaver
Danley Sound Labs

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Stephen Swaffer

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Re: QSC Jumps in with both feet.
« Reply #18 on: November 14, 2014, 08:45:53 AM »

This may seem odd, but from my experience I would think drawing from from the model of arc welder ratings might make sense.  Both are power output devices with thermal as well as peak limitations.  Arc welders usually have a duty cycle rating on them-x number of amps continuous, x number at 80%, 60% and so on-then the on time for the duty cycle is expressed-2 minutes say or whatever.

I had an issue at a former job-we had  both Miller and Lincoln TIG welders rated the same output amps.  One had a problem in a weld booth so we swapped it out and at the time our spare was the other brand.  Very quickly we got a call that the welder kept shutting down.  After verifying fans were running, etc. and learning that the process in this booth was running at max output, I pulled out the manuals-and sure enough the duty cycle on the welder we had put in there was lower than the other brand.  John Q Public aside, I hard a tough time convincing engineers this was the problem though it was easily verified!

It would be possible to create a duty cycle chart with various lengths of peaks while running a specified continuous power.  IMO this would give a great deal of information.  Unfortunately, the more detail and more complex your specs the fewer people there are that will understand them or use them, as has been pointed out. So the ROI for the manufacturers isn't there.
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Steve Swaffer

David Parker

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Re: QSC Jumps in with both feet.
« Reply #19 on: November 14, 2014, 09:01:43 AM »

This may seem odd, but from my experience I would think drawing from from the model of arc welder ratings might make sense.  Both are power output devices with thermal as well as peak limitations.  Arc welders usually have a duty cycle rating on them-x number of amps continuous, x number at 80%, 60% and so on-then the on time for the duty cycle is expressed-2 minutes say or whatever.

I had an issue at a former job-we had  both Miller and Lincoln TIG welders rated the same output amps.  One had a problem in a weld booth so we swapped it out and at the time our spare was the other brand.  Very quickly we got a call that the welder kept shutting down.  After verifying fans were running, etc. and learning that the process in this booth was running at max output, I pulled out the manuals-and sure enough the duty cycle on the welder we had put in there was lower than the other brand.  John Q Public aside, I hard a tough time convincing engineers this was the problem though it was easily verified!

It would be possible to create a duty cycle chart with various lengths of peaks while running a specified continuous power.  IMO this would give a great deal of information.  Unfortunately, the more detail and more complex your specs the fewer people there are that will understand them or use them, as has been pointed out. So the ROI for the manufacturers isn't there.
the welder analogy is valid. With stick-rod, the transformer gets a break while the welder changes rods. With TIG, the current draw is for a much longer time, less breaks.
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Re: QSC Jumps in with both feet.
« Reply #19 on: November 14, 2014, 09:01:43 AM »


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