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Best power amp for pre/power rig

#21
paulraphael said:
I'm talking about a subjective definition, which involves listening to them.

I suspect that's the defintion Tombowlus is using too.

I'm not sure if you're calling any phenomenon that isn't predicted by Audio Engineering 101 a mythology. I think the less defensible mythology is the assumption that a handful of measurements, based on sinewave test signals, can adequately predict the psychoachoustic experience of listening to music.
Click to expand...

Beyond Stereophile-type mythology, in real-world performance, amplifiers that produce identical signals will actually sound identical. Amps that sound different produce signals that aren't identical. Period. Good amps produce signals that are simply larger versions of the input signals, without adding or taking away any sonic quality. It's all in the signal--whether it's soundtage, detail, extension, etc.

Sonic differences are often heard in modern power amps in sighted comparisons, in non-level-matched ones, in comparisons done with non-same program material, and in comparisons done with non-same loudspeakers and/or listening environments. These anecdotal accounts are not necessarily without merit, but they don't carry any particular weight, either, because they don't account for biases, whether they are intentional or not. In level-matched double-blind tests, these differences seem to nearly always melt away. Why is that?

What sinewave tests are you talking about? How do you feel about non-sinewave tests, too? I understand that if an amplifier to someone is just some mysterious box with gee-whiz stuff in it that may have some magical properties if it looks and feels and is priced exotically enough, that person will easily believe that amplifier design and performance is some sort of magical, unknowable thing. Please understand, though, that there are people who understand what power amps do.
 
#22
Bob, you still make two assumptions:

1) that in your comparisons, you are measuring everything that is relevent;

2) that the measurements of these amps ARE in fact identical.

Regarding the first assumption, I have yet to see any published psychoacoustic research that claims we know all the parameters of an audio signal that the human ear can distinguish.

Regarding the second assumption, I have yet to see two amplifiers (particularly at widely divergent price points) that measure identically, even with matched gains.

I have also never seen a proposed test or suite of tests for amplifiers that's exhaustive even terms of the many known variables--like complex speaker impedance curves. Typically, for the sake of taming the amount of data, and avoiding the need for complex 3-dimensional plots, one variable is always held constant. This tends to create a world that's quite simple compared with a musical signal.

Here's an interesting level-matched blind test, which you might dismiss because of its source, but i find the methodology sound and the analysis interesting (it goes on for a lot of pages). Both amps in question are likely higher quality designs than what we typically use (and can afford) for bass:

http://stereophile.com/features/113/index.html
 
#24
No, I make neither assumption, nor have I promoted either. The proof of the pudding, so to speak, is in listening tests concerning sound alone and not visual/marketing/voodoo biases (i.e., double-blind tests), which tend to support my position.

You falsely presume that amps are inherently sonically different from one another; therefore even if they sound alike you will tend to conclude that they sound different.

Stereophile of course considers double blind tests that disprove their presumptions and biases and desired outcomes to be flawed. What? they can't possibly be the same!! We know they're different!! Oh dear!! Come on, even figure skating has at least tried to move away from foregone conclusions.

If a car magazine were staffed by writers and editors who willfully cultivated their own technical ignorance of how and why cars ran and handled the way they do, they'd be laughed out of the marketplace. But because it's audio, with advertisers with products that defy the laws of physics and with "golden ears" egos …

I believe you when you when you say you've never seen a proposed test or suite of tests for power amplifiers that is exhaustive. Most people haven't unless they're actually involved in design and manufacturing of amplifiers in a solid engineering environment.
 
#25
Bob Lee (QSC) said:
No, I make neither assumption, nor have I promoted either. The proof of the pudding, so to speak, is in listening tests concerning sound alone and not visual/marketing/voodoo biases (i.e., double-blind tests), which tend to support my position.

You falsely presume that amps are inherently sonically different from one another; therefore even if they sound alike you will tend to conclude that they sound different.

Stereophile of course considers double blind tests that disprove their presumptions and biases and desired outcomes to be flawed. What? they can't possibly be the same!! We know they're different!! Oh dear!! Come on, even figure skating has at least tried to move away from foregone conclusions.

If a car magazine were staffed by writers and editors who willfully cultivated their own technical ignorance of how and why cars ran and handled the way they do, they'd be laughed out of the marketplace. But because it's audio, with advertisers with products that defy the laws of physics and with "golden ears" egos …

I believe you when you when you say you've never seen a proposed test or suite of tests for power amplifiers that is exhaustive. Most people haven't unless they're actually involved in design and manufacturing of amplifiers in a solid engineering environment.
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Your previous post regarding 'the signal', is what I believe paulraphael was addressing.

You basically said if the gain is matched the signal will be matched and the sonic results will be indistinguishable.

I believe what paulraphael was saying was that the signal may be more complex than what we have the capabilities to measure.
[I appologize in advance if I'm misinterpreting what paulraphael intended.]

My feeling is if one amp sounds better to me than another amp (even if the lesser-liked amp is louder (while still operating within its design parameters)), I prefer the better sounding amp.
I don't care if my preference is totally psychological or if my ears are actually perceiving something different between the two.
My ears and my brain are telling me something and you are telling me that the difference is just 'in my head'.
At the end of the day, better to my ears and brain is still better to me personally (obviously, not to you).

I agree with your stressing that matching gains is very important when comparing amps.
That is very important.
But when the amp preferred is the lower (or equal) setting of gain amp, then I just go with my ears and brain.
Thank you very much.
 
#28
ge9375 said:
Wait, so my tone will improve if I put a different logo on my existing power amp?
Click to expand...

You just hit on the idea for a small business. "High-End Logos.com"
Why spend thousands for one of these boutique amps when you can have all the perceived sound for just a few bucks?

For my next research, I'm going to see if my playing gets better when I wear a Jaco wig.
 
#29
lo-freq said:
I believe what paulraphael was saying was that the signal may be more complex than what we have the capabilities to measure.
Click to expand...

Or, in some cases, what we have the inclination to measure. Bob suggests that Stereophile Magazine is all about subjective voodoo, but they in fact have an engineer on staff who provides objective measurements to accompany the longer, more fanciful reviews. He uses a bigger suite of measurements than the ones I've seen published by manufacturers (he includse more complex ones than anyone would be inclined to use for marketing, which seems to be the prime motivation of measurements in the industry). And wouldn't you know it, different amps seem to measure quite differently.

Here are just a handful of random examples (the last two are expensive tube designs):

[Invalid or Expired Link Removed]
http://stereophile.com/solidpoweramps/406halcro/index4.html
[Invalid or Expired Link Removed]
[Invalid or Expired Link Removed]
[Invalid or Expired Link Removed]
http://stereophile.com/tubepoweramps/843/index6.html
[Invalid or Expired Link Removed]
 
#31
Bob Lee (QSC) said:
You falsely presume that amps are inherently sonically different from one another; therefore even if they sound alike you will tend to conclude that they sound different.
Click to expand...

That's just a presumption on your part. I've in fact listened to amps that I couldn't tell apart. And not in blind tests ... in situations where I knew i was switching from amp 1 to amp 2, and they sounded alike.

In my mind this gives a bit of extra credence to the instances when they don't sound alike.
 
#32
I do think that players tend to join one camp or another for various reasons. And, we can read specs for ever and it's all talk and paper. I've never been able to hear any difference between 2 top quality amps from different manufactures but, when using them in a bass rig, I think that different brands of power amps seem to respond differently to the way I play. The power-amp is really part of a total instrument and not just a part of the signal chain, so ANY slight differencies will be magnified by the fact that the PLAYER is also the LISTENER.
 
#33
lo-freq said:
Your previous post regarding 'the signal', is what I believe paulraphael was addressing.

You basically said if the gain is matched the signal will be matched and the sonic results will be indistinguishable.

I believe what paulraphael was saying was that the signal may be more complex than what we have the capabilities to measure.
[I appologize in advance if I'm misinterpreting what paulraphael intended.]

My feeling is if one amp sounds better to me than another amp (even if the lesser-liked amp is louder (while still operating within its design parameters)), I prefer the better sounding amp.
I don't care if my preference is totally psychological or if my ears are actually perceiving something different between the two.
My ears and my brain are telling me something and you are telling me that the difference is just 'in my head'.
At the end of the day, better to my ears and brain is still better to me personally (obviously, not to you).

I agree with your stressing that matching gains is very important when comparing amps.
That is very important.
Click to expand...

What I'm saying is that amps that produce identical signals will sound the same. Note that "measuring" is not used anywhere in that sentence. I haven't been bringing up "measuring." I'm not hung up on "measuring."

The ideal power amp is metaphorically a "straight wire with gain." Therefore, the design ideals are to create power amps that only amplify the signal but no not change it in other ways. A power amp's job is not to itself sound good or bad--that should be determined by what goes into it (the input signal) and what the output signal goes into (the loudspeakers and the acoustical environment). It's job is to be neutral. If you put crap in, you should get crap out, and if you put cream in, you get cream out. It's not the amp's job to add "detail" or "warmth" that isn't already there. It's not the amp's job to clean up or add effects--that's typically something you do at the line-level stage.

How difficult is it to make amps that reproduce the input signal with ultra-accuracy, up to the point where the output clips? It's not rocket science any more and hasn't been for a good 20 years or so. The PLX and CA amps are good examples of amps that are superbly accurate and would even make good studio reference amps (their fan cooling would be a detriment).

If two power amps sound different, at the same gain and with the same input signal and into the same loudspeakers, et al, then at least one of them is doing something to alter the signal. If an anomaly can be heard, it can certainly be identified--measured, if need be--and corrected. That's what competent engineering is for.

Amps that do an extremely good and accurate job of reproducing the input signal--and there are quite a few of them, and sorry, paulraphael, they don't necessarily cost a great deal--will sound alike when their gains are matched when you put the same signal into them and listen to them through the same loudspeakers, etc. The loudspeakers, after all, are just responding to signal. They do not change their response to a signal as a result of being impressed by the brand or finish or reviews of the amp driving them.

But when the amp preferred is the lower (or equal) setting of gain amp, then I just go with my ears and brain.
Click to expand...

Sorry, I don't understand what you're saying here.
 
#34
paulraphael said:
That's just a presumption on your part. I've in fact listened to amps that I couldn't tell apart. And not in blind tests ... in situations where I knew i was switching from amp 1 to amp 2, and they sounded alike.

In my mind this gives a bit of extra credence to the instances when they don't sound alike.
Click to expand...

No, I'm not presuming that. In another thread you named some amps that you believe will not perform well even though you offered no basis for that other than their brand names. That is presumption.

I duly note that you have listened to amps that you couldn't tell apart. Thank you.
 
#35
GreyBeard said:
I do think that players tend to join one camp or another for various reasons. And, we can read specs for ever and it's all talk and paper. I've never been able to hear any difference between 2 top quality amps from different manufactures but, when using them in a bass rig, I think that different brands of power amps seem to respond differently to the way I play. The power-amp is really part of a total instrument and not just a part of the signal chain, so ANY slight differencies will be magnified by the fact that the PLAYER is also the LISTENER.
Click to expand...

You can read specs, but don't expect them to tell much. They don't necessarily lie, unless the manufacturer is unethical, but they are at best only sketchy descriptions of a product that can at best give a vague idea of what it can do. I don't think the solution is "more specs" either; you can look at an engineering group's large binder full of tests on an amplifier model and still not know what the engineers were experiencing.

If power amps do respond differently to how you play, then at least one of them is defective or poorly designed. ;)
 
#37
paulraphael said:
marketing, which seems to be the prime motivation of measurements in the industry).
Click to expand...

Marketing is the prime motivation of publishing specs; engineering is the prime "motivation" of measurements.

And wouldn't you know it, different amps seem to measure quite differently.
Click to expand...

They may very well measure differently yet sound the same. That happens all the time. Not everything that can be detected with instrumentation can be heard.
 
#38
Has anyone ever taken plot of the waveforms created by two different amps, into matching speakers with matched gain. Surely if the plots are identical then the amps sound identical. If not, then they must sound different. And if they do not match the plots from the line level source that is driving them, then they must be adding colouration.

Does anyone have the gear to do this?

Alex
 
#39
Bob Lee (QSC) said:
Amps that do an extremely good and accurate job of reproducing the input signal--and there are quite a few of them, and sorry, paulraphael, they don't necessarily cost a great deal--will sound alike when their gains are matched when you put the same signal into them and listen to them through the same loudspeakers, etc.
Click to expand...

Perhaps we're disputing what constitutes an "extremely good and accurate job of reproducing the input signal." From the dozens of measurements I've found of power amps, none of them responds identically; there are many easily measured differences. Which differences are significant or not is probably at the heart of the matter. Current psychoachoustic research has a lot to say on this (which kinds of distortions matter the most, etc.) but no one in that field claims to know the whole story. It's a young, young field.

Bob Lee (QSC) said:
The loudspeakers, after all, are just responding to signal. They do not change their response to a signal as a result of being impressed by the brand or finish or reviews of the amp driving them.
Click to expand...

That's a clever and condescending way of putting it. It also ignores that a speaker (unlike a fixed impedance test load) presents a reactive load to the amplifier. Speaker impedences change in complex ways in relation to signal frequency and amplitude. So an amp is going to respond in very different ways to different speakers (and will respond to all of them in different ways from the simulated loads used on the test bench). It's possible for a particular set of speakers to illuminate a difference between two amplifiers that truly didn't exist in a lab environment with a speaker simulating load.
 
#40
Could we get back on topic here? I'm interested in the results of this discussion. (Not that Bob and paulraphael's discussion isn't interesting)

One disadvantage I see to the Crown MA-2400 is that it does not have Speakon outputs. I need an amp with two of those.

I'd also like something light.

Currently my eye is on on the QSC PLX-1804, or if I get to feeling really frisky, maybe the 3602.

I'm looking to match that up to an Avalon U5 as a preamp, a Whappo Grande and El Whappo cabinet (but looking at the specs, it doesn't look like those two cabinets have the same impedance, so I don't know what the deal is with that).

Also, please don't just state, "______ power amp rules!". That's not really helpful. Please justify.

Thanks!
 

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