Crown XLS2502 Stereo Amplifier Review

[March Audio]

Same arguments, different review... As if we did not have a topic for that already.

It is indeed frustrating that some keep resorting back to the same old blinkered thinking and posting it at every single review.

 

[restorer-john]

John, the fact that you resort to this demonstrates you know the flaw in your argument.

You are even conflating power output and frequency response.

Oh dear. You don't do a swept frequency response plot from 20-20KHz at full rated power to look for issues at each end of the spectrum? You don't compare that to a 1W or half rated power to investigate power bandwidth issues?

 

[restorer-john]

It is indeed frustrating that some keep resorting back to the same old blinkered thinking and posting it at every review.

There's only one person in this thread cutting and pasting the same irrelevant things and it isn't me.

 

[March Audio]

Oh dear. You don't do a swept frequency response plot from 20-20KHz at full rated power to look for issues at each end of the spectrum? You don't compare that to a 1W or half rated power to investigate power bandwidth issues?

John, this is so tedious. It is not a real world requirement for an amplifier to have the same 1kHz rated power output at 20kHz.

The reality is amps will generally increase distortion as the frequency rises. Does that mean they are broken? No.

 

[March Audio]

There's only one person in this thread cutting and pasting the same irrelevant things and it isn't me.

John, this may be uncharitable but you do this at every single review.

You criticise what Amir has done, what tests he hasnt performed, the faults with the tests he has performed, without any thought about the real world relevance or the broader goals of the site.

I havent said dont do power V Frequency testing - I have questioned the real world relevance and importance. You take it as being some kind of direct relevance and highly important to real world audio quality, when it is not that simple and totally misleading to think so.

 

[Alice of Old Vincennes]

John, this may be uncharitable but you do this at every single review.
You criticise what Amir has done, what tests he hasnt performed, the faults with the tests he has performed, without any thought about the real world relevance or the broader goals of the site.
I havent said dont do power V Frequency testing - I have questioned the real world relevance and importance. You take it as being some kind of direct relevance and highly important to real world audio quality, when it is not that simple and totally misleading to think so.

 

[LTig]

Can you explain to me what's the point of testing (in this publication - consider the wider audience) for a condition that will never exist in the real world? You will never see full power at 20kHz, not even vaguely close to it, so can you explain to me why you consider it so important?

It's a pro amp and may be used behind a crossover to feed an array of tweeters.

 

[Francis Vaughan]

Agree.
+ Slew Rate and Damping Factor.

These are both useless metrics. As I described earlier, damping factor is at best a surrogate for feedback factor, and otherwise has no influence on the final sound, and slew rate is also related to descisions in feedback design. Neither have a direct influence on the actual sound, and are only correlated with amplifier performance because they are influenced by, or the result of design descisions. We seem to be in a time warp quoting these useless metrics. Back in the 80's they were all the rage. If your amplifier is competently designed these numbers will usually look good, but that is a consequence of the design regime. You may as well add mass of the amplifier to the list. It too is a consequence of the design choices, but has just as much direct effect on the sound.

 

[levimax]

@Amir, @Restorer John, and @March Audio are 3 of my favorite contributors to this site and in this case I can understand their different points of view on amplifier testing as they are all reasonable and valid. I agree with Restorer John's point that the tests should be consistent regardless of the type of amplifier being tested and the reader needs to learn how to interpret them. I think John's point is that it can appear that tests that show the limitations of traditional amps like SINAD and "32 tone tests" are always done but tests that show the limitations of Class D like maximum power vs frequency or square wave are not. While I understand "full power at 20 Khz" is not important to real world listening I have found that limitations like this indicate "something" about that amp that may be important (All filters have "consequences" beyond their primary function like phase shift and transient response).... at the very least it is interesting to learn about and understand the different strengths and weaknesses and I see no reason not to test all amps consistently and thoroughly.

 

[Alice of Old Vincennes]

@Amir, @Restorer John, and @March Audio are 3 of my favorite contributors to this site and in this case I can understand their different points of view on amplifier testing as they are all reasonable and valid. I agree with Restorer John's point that the tests should be consistent regardless of the type of amplifier being tested and the reader needs to learn how to interpret them. I think John's point is that it can appear that tests that show the limitations of traditional amps like SINAD and "32 tone tests" are always done but tests that show the limitations of Class D like maximum power vs frequency or square wave are not. While I understand "full power at 20 Khz" is not important to real world listening I have found that limitations like this indicate "something" about that amp that may be important (All filters have "consequences" beyond their primary function like phase shift and transient response).... at the very least it is interesting to learn about and understand the different strengths and weaknesses and I see no reason not to test all amps consistently and thoroughly.

 

[Francis Vaughan]

It's a pro amp and may be used behind a crossover to feed an array of tweeters.

It might be. So choose an amp specifically designed for the purpose. Active crossovers are a perfect example of why you don't need flat power delivery across the audio spectrum. At least not continuous flat power delivery. Any active system places much more power into the lower frequencies. This is simply because that is where it is needed for real world signals. Using the same power capability amplifier for your bass drivers as the top end is just wasting money.

This is a lower end pro-amp. It isn't the sort of thing you would expect to see in an active array. You might see it used for simple vocal reinforcement for an otherwise un-amplified act, or maybe for foldback. It is designed for its use case, and optimised around that. That use case drives the technical requirements, and the price point drives the realisation. Demanding unnecessary restrictions in the technical requirements just drives the price up, or the quality down for the same price, and you end up with an objectively poorer product. This is true no matter what the price point.

 

[DonH56]

One thing to keep in mind is that there can be 20 kHz (and above) content riding on a larger (generally lower-frequency) signal. Even if the 20 kHz content is low, it can still span the full-power (voltage) range of the amplifier.

 

[restorer-john]

John, this may be uncharitable but you do this at every single review.

You criticise what Amir has done, what tests he hasnt performed, the faults with the tests he has performed, without any thought about the real world relevance or the broader goals of the site.

I haven't said don't do power V Frequency testing - I have questioned the real world relevance and importance. You take it as being some kind of direct relevance and highly important to real world audio quality, when it is not that simple and totally misleading to think so.

That's complete rubbish, Alan, and you know it.

Amir receives in equal quantity, both bouquets and brickbats from me and others, and to state otherwise is plain disingenuous. When he openly considers a further watering down of testing, I'm certainly not the only one around here who thinks it is a big mistake.

My position is backed by the US Federal Trades Commission, Amplifier Rule. If you, or anyone else wants to advertise and sell amplifiers in the US (and other countries benefiting from those standards), they must do so under that rule. Several times the industry has tried unsuccessfully to water down the rules and been over-ruled in no uncertain terms. Minor changes were made to preconditioning, allowances for multi-channel AVRs and powered subwoofers, but the rest is left untouched.

Again in 2000 and 2002 and another statement in 2007 essentially leaving it untouched. You can research it yourself.

It applies to you and your amplifiers. They must be able to achieve their rated power and distortion over the advertised bandwidth. Any frequency at full power for 5 minutes. Whether you think it is reasonable or not, doesn't matter one iota. If you want to change it- petition the FTC, in the meantime, ensure your amplifiers are compliant. You can't change the rule by banging on here, and every time you do, I and others will remind you you are barking up the wrong tree- again.

This site cannot and should not become a platform for promoting the weakening of standards, one driven by conflicts of interest and whatever the latest flavour-of-the-month amplifier happens to be.

So, instead of untruths and attempts to silence any voices of dissent, go get the rules changed in your favour. Or play by them.

 

[Francis Vaughan]

This is a consumer protection rule. It does not provide ironclad guidance on the scientific objective performance of an amplifier in real life. Nor does it pretend to. It just stopped the stupid marketing, and only for home entertainment. A site that intends to provide scientifically justifiable guidance needs to go beyond consumer protection legislation. Sure, it is reasonable that compliance with the stated specs relative to that rule should be measured, but only in the sense that it verifies that the manufacturer is meeting stated specs. We expect insights that go beyond this. If the amplifier has aurally important performance that is quantifiable outside of 1974 consumer law, then we should see it.
The rules are ones of objective scientific facts. A 1974 law is not one of these.
The 1974 rules brought about a golden time of honesty in marketing, something most of audio is sadly deficient in. But they didn't add to the science, and still don't.
Indeed there is a case to be made that the 1974 rules actually stymied progress. Amplifiers with high peak power output, designs that objectively produced better aural results, were hard to market. They had to be sold only at the continuous (essentially thermally limited) power, and the peak power delivery only quoted as an afterthought. This isn't to say that overall the rule has not been of great benefit to the average consumer. But be clear about who the rule serves and why.

 

[jhaider]

Would love myself some big CV speakers for surround sound.

I recall there was a CV line designed by an ex-NHT engineer that was voiced fairly neutral but had really big drivers and big cabinets? I do not remember anything further, sorry.

 

[amirm]

I don't think the issues here are clear. This is more or an instrumentation problem than a device problem.

The power graph is not just showing power at certain frequency. It attempts to determine by trial and error, how much power can be delivered using a set percentage for THD+N. For THD to make sense at 20 kHz, you have to have enough bandwidth after that to capture its harmonics. Standard test has 90 kHz bandwidth. Class AB devices are clean above 20 kHz so you can measure true harmonics of 20 kHz. Class D amps on the other hand, routinely have noise shaping that puts garbage above audible band. I showed this in my review:

Notice how there is rising noise until we get to 100 kHz. This noise forces THD+N to increase sharpy above 20 kHz.

Now, if I set THD+N to a high value, you will indeed see full power at all frequencies. If I set it too low (e.g. 0.1%) you will see a fraction of "power" with that much THD+N which is dominated by +N. This leads people to think the amp can't deliver power at high frequencies which is not right.

So bottom line, this is not a question of how much power you can have at 20 kHz. It is the question of how you measure just the harmonic distortion.

With respect to non-linearities, I already post the 32-tone signal:

So we have that measure of non-linearity already.

 

[March Audio]

That's complete rubbish, Alan, and you know it.

Amir receives in equal quantity, both bouquets and brickbats from me and others, and to state otherwise is plain disingenuous. When he openly considers a further watering down of testing, I'm certainly not the only one around here who thinks it is a big mistake.

My position is backed by the US Federal Trades Commission, Amplifier Rule. If you, or anyone else wants to advertise and sell amplifiers in the US (and other countries benefiting from those standards), they must do so under that rule. Several times the industry has tried unsuccessfully to water down the rules and been over-ruled in no uncertain terms. Minor changes were made to preconditioning, allowances for multi-channel AVRs and powered subwoofers, but the rest is left untouched.

View attachment 44108

Again in 2000 and 2002 and another statement in 2007 essentially leaving it untouched. You can research it yourself.

It applies to you and your amplifiers. They must be able to achieve their rated power and distortion over the advertised bandwidth. Any frequency at full power for 5 minutes. Whether you think it is reasonable or not, doesn't matter one iota. If you want to change it- petition the FTC, in the meantime, ensure your amplifiers are compliant. You can't change the rule by banging on here, and every time you do, I and others will remind you you are barking up the wrong tree- again.

This site cannot and should not become a platform for promoting the weakening of standards, one driven by conflicts of interest and whatever the latest flavour-of-the-month amplifier happens to be.

So, instead of untruths and attempts to silence any voices of dissent, go get the rules changed in your favour. Or play by them.

The FTC rule whilst is correct in intention, to protect consumers, it is utterly useless as an indicator of amplifiers comparative quality.

These rules have been long contested by manufacturers for good reason. They impose requirements such as totally unnecessary large heatsinks which incur cost which ironically ends up coming out of the consumers pocket. Just to pass a test situation which will never occur in the real world.

You havent technically contradicted anything I have said, so you know full well there are no untruths here. Give it a rest with the implied self interest biasing my views.

My amps pass these tests as you know - Im just applying a bit of critical thought to their relative importance. I have not said dont test, but Im just a little tired of hearing your proclamations in every single review that Amir does that they are somehow all fatally flawed because you are stuck in 1970's thinking.

 

[amirm]

It applies to you and your amplifiers. They must be able to achieve their rated power and distortion over the advertised bandwidth.

You sure this rule applies to commercial products like the amp we are discussing?

Also, that rule is with respect to advertising. All pro amp products violate that rule left and right so not sure what value it has for that market. Here are the crown specs:

They are saying the power numbers are only for 1 kHz.

 

[oldsysop]

These are both useless metrics. As I described earlier, damping factor is at best a surrogate for feedback factor, and otherwise has no influence on the final sound, and slew rate is also related to descisions in feedback design. Neither have a direct influence on the actual sound, and are only correlated with amplifier performance because they are influenced by, or the result of design descisions. We seem to be in a time warp quoting these useless metrics. Back in the 80's they were all the rage. If your amplifier is competently designed these numbers will usually look good, but that is a consequence of the design regime. You may as well add mass of the amplifier to the list. It too is a consequence of the design choices, but has just as much direct effect on the sound.

Of my 6 amplifiers the newest is from 1979

 

[March Audio]

@Amir, @Restorer John, and @March Audio are 3 of my favorite contributors to this site and in this case I can understand their different points of view on amplifier testing as they are all reasonable and valid. I agree with Restorer John's point that the tests should be consistent regardless of the type of amplifier being tested and the reader needs to learn how to interpret them. I think John's point is that it can appear that tests that show the limitations of traditional amps like SINAD and "32 tone tests" are always done but tests that show the limitations of Class D like maximum power vs frequency or square wave are not. While I understand "full power at 20 Khz" is not important to real world listening I have found that limitations like this indicate "something" about that amp that may be important (All filters have "consequences" beyond their primary function like phase shift and transient response).... at the very least it is interesting to learn about and understand the different strengths and weaknesses and I see no reason not to test all amps consistently and thoroughly.

You need to bear in mind that this amp is different to most in that i has an ADC at the front end which sharply limits bandwidth hence things like square wave testing become pointless.