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Author Topic: Power Amp Quality  (Read 18820 times)

John Roberts {JR}

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Re: Power Amp Quality
« Reply #10 on: March 22, 2015, 04:27:37 pm »

I have to disagree on this one. Just last week as part of a training event, we did have a number of amps lined up, all from premium brands, and there were very obvious differences in how they sounded.

We were connected to 8 ohm loudspeakers and running at a moderate level, nowhere near stressing any of the amps and the differences were definitely there.

The power amp may not be the point in the signal chain where the biggest differences will be noticed between products but if you listen, you will hear that all amps aren't alike.

I try to make a point of not arguing with people on the internet about what they think they heard, but to second Ivan's post, it is "extremely" difficult to perform a listening test where all the variables are completely controlled for (eliminated). So while you may think you were hearing differences between those amps there is a good chance you were hearing faults in the test.

Ivan and I have probably run more listening tests than you have listened to, but maybe both of us are wrong...  8)

Do you feel lucky?

JR 
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Ivan Beaver

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Re: Power Amp Quality
« Reply #11 on: March 22, 2015, 05:05:55 pm »

I try to make a point of not arguing with people on the internet about what they think they heard, but to second Ivan's post, it is "extremely" difficult to perform a listening test where all the variables are completely controlled for (eliminated). So while you may think you were hearing differences between those amps there is a good chance you were hearing faults in the test.

Ivan and I have probably run more listening tests than you have listened to, but maybe both of us are wrong...  8)

Do you feel lucky?

JR
It is REAL easy to hear something-if you want to.

How many times have people "thought" they were adjusting an eq, on ly to find out it was the wrong channel OR the eq was bypassed.

If you haven't don this, then EITHER you are LYING-or you haven't done it enough.

Heck you "listen close enough", you can simply mute and unmute a channel with some playback on it and "hear" some subtle differences and "think" you are hearing something.

The REAL test to see if you are hearing something or not is to be able to do it in a blind test. 

If you can't do it in a blind test-then it is simply not worrying about.

We were doing some listening tests on amps and "sound quality" not to long ago.

I built a switcher that would switch a SINGLE speaker between 2 amplifiers.

If we listened REAL HARD, we could "tell" a difference between when we switched between A and B.

HOWEVER we could hear NO difference when we switched between B and A.

We did this MANY times, and everybody agreed they heard "something", but could not say what it was.

The best I can "attribute" this to was the time (in microseconds) that it took to switch between A and B was longer than the time it took to switch between B and A-due to the speed of the switch contacts.

The "acoustic memory" is VERY short and it is real easy to "fool" somebody into hearing something-by verbal or physical clues.

BTW, doing a "amp listening" test- you can ONLY use ONE loudspeaker.

NOT a "matched pair".  I tried this one time and we would all pick one channel over the other-depending on what we were listening to.  WIth a different song-we would pick the other channel.

This went back and forth until I changed the setup and we just used ONE speaker-then we could not tell the difference.

And while the speakers were matched to within 1/4dB or so-that was still enough of a difference for us to "pick out" certain things that we preferred over the other.

But as I said-those preferences kept changing with the program material.

To me there are more important things than "the sound of an amp" that make me buy one over the other.
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Luke Geis

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Re: Power Amp Quality
« Reply #12 on: March 22, 2015, 05:10:18 pm »

There is no excuse these days to make an amp that uses any class of power amplification that isn't linear from 20-20 within an exceptionable range. Where the weaknesses show is when they are used in such a manor that exploits that weakness. High levels, weak/high supply voltage ( as from the outlet in a house ), sine wave, pink noise, bursts ( like a kick hit ), temperature, Perhaps damping factor ( shown basically to be a moot factor ) and even the load itself can make an amp show it's weaknesses. Some amps have higher levels of distortion when running low impedance speakers. 8 ohms. seems to be the most stable and distortion free for most though.

How close in proximity to each test you ran may have an impact on the performance. Power compression is a very real phenomenon and if one amp change to the next was quick enough, a cold amp and a warm speaker coil could have had an impact? Perhaps there was a difference? The argument is then, did any one amp sound bad, or were they relatively the same? Sounding different is not much of a valid input. It's not quantifiable if the test was flawed. A difference of +/- 3db is said to be acceptable. It very well could be that the +/- 3db for that amp was at the same +/- 3db for the speaker which would mean the amp/speaker combination is not ideal. Perhaps the reason most manufacturers would prefer you use the specified amps? The way you test has to leave out all other forms of what if's. You want to have quantifiable results that show only the performance of the amp. That result is what we are saying is common amongst the majority of amps theses days. They are so close from one end of the spectrum to the other, that an amp that works is pretty much a good amp. Now when you start getting into the weaknesses of an amp and where it starts to fall apart, that is where money changes the game. You could not expect a Behringer EP-2500 to outperform a similar Lab-Gruppen type model now would you? Chances are good that they will both sound acceptable under normal conditions. When the abuse starts to come in, the weaknesses come out.

I have never ran a show where I could ever blame the amp as being the weak link. As long as I ran things within the operating parameters, I got results consistent with the amp/speaker/equipment combination.
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Jim McKeveny

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Re: Power Amp Quality
« Reply #13 on: March 23, 2015, 11:54:56 am »

In no particular order, I think most non amp-designer buyers would like standardized for comparison:

"First Watt" performance.

"Last Watt" performance.

"Duty Cycle"

I used quotes because these are imperfect constructs and subject to ongoing argument...

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Steve M Smith

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Re: Power Amp Quality
« Reply #14 on: March 23, 2015, 11:59:05 am »

How many times have people "thought" they were adjusting an eq, on ly to find out it was the wrong channel OR the eq was bypassed.

If you haven't done this, then EITHER you are LYING-or you haven't done it.
I did it last night.  I was adjust the singer's EQ and I was sure I could hear a difference then realised I had the wrong channel selected.

We did this MANY times, and everybody agreed they heard "something", but could not say what it was.
You can get a similar but even more pronounced perceived difference with something like an acoustic guitar going through a preamp with a polarity switch (incorrectly marked pahse).  If you switch it over whilst playing, it seems to give an obvious change but if you stop, switch it over then start to play, it sounds the same.



Steve.
« Last Edit: March 23, 2015, 12:02:48 pm by Steve M Smith »
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John Roberts {JR}

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Re: Power Amp Quality
« Reply #15 on: March 23, 2015, 12:01:10 pm »

In no particular order, I think most non amp-designer buyers would like standardized for comparison:

"First Watt" performance.

"Last Watt" performance.

"Duty Cycle"

I used quotes because these are imperfect constructs and subject to ongoing argument...

 ;D ;D ;D 

Trouble maker...

JR
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Greg_Cameron

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Re: Power Amp Quality
« Reply #16 on: March 23, 2015, 02:32:18 pm »

I'm curious if anyone has noticed a difference between old school class AB through H vs. any of the class D variants where the frequency response of the amp can be altered by the RC network formed by the load. I recall some testing posted here when the first I-Techs shipped noting high frequency roll-off relative to other amps due to output topology.
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John Roberts {JR}

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Re: Power Amp Quality
« Reply #17 on: March 23, 2015, 02:57:47 pm »

I'm curious if anyone has noticed a difference between old school class AB through H vs. any of the class D variants where the frequency response of the amp can be altered by the RC network formed by the load. I recall some testing posted here when the first I-Techs shipped noting high frequency roll-off relative to other amps due to output topology.
While the load interaction is related to the class D amp's need for an output filter, the pole frequency dipping down into the audio passband was related to one amp model's specific design trade-off and is not inherent in all Class D amps. (I suspect  they could have used the on-board DSP to correct for this). I recall Langston making a big deal about this but he was more measurement centric than most, kicking the tires on the then new amps. 

This was not unknown and easily compensated for with EQ, if important for the specific application.

I suspect most modern amps of all classes deliver on their specified power bandwidth.

JR

PS: Look at the frequency response plot for your speakers or microphones at 20kHz.
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Greg_Cameron

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Re: Power Amp Quality
« Reply #18 on: March 23, 2015, 03:03:29 pm »

PS: Look at the frequency response plot for your speakers or microphones at 20kHz.


Right? ;)
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Ivan Beaver

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Re: Power Amp Quality
« Reply #19 on: March 23, 2015, 05:15:37 pm »

I'm curious if anyone has noticed a difference between old school class AB through H vs. any of the class D variants where the frequency response of the amp can be altered by the RC network formed by the load. I recall some testing posted here when the first I-Techs shipped noting high frequency roll-off relative to other amps due to output topology.
Sometimes people get "hung up" on something-without realizing how much or how little difference it makes.

While it true there can be some HF rolloff-it is usually in the dB or so category at the high freq.

To be honest-if 15K changed up or down by 1 dB, I would not be able to notice.

And consider (as JR pointed out) the HF response of most cabinets is pretty much "history" by the time it gets to 15K.

So while "technically" the HF is rolling of-I doubt many (in fact very few) people would even realize it.

Just because we can measure it-does not mean that we can easily hear it.

I am not saying it is not important to realize this-but somethings get "blown out of proportion", when they really should not.
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Ivan Beaver
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ProSoundWeb Community

Re: Power Amp Quality
« Reply #19 on: March 23, 2015, 05:15:37 pm »


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