Classe CT-2300 Stereo Power Amplifier Review

[Irvrobinson]

I'm not dissing the review nor do I intend to but I can't help feel that "audiophile" crept into this review when discussing how the amps sound differently and how the Classe "hanging" with the upper crowd.

I hear you. The problem of gauging subtlety and its audibility is difficult. For example, do Pass Labs amps really sound different because Nelson has apparently figured out how to get the vast majority of distortion to be second or third harmonics, while most other amps have greater proportions of high order distortions? At -65db or less? Could a DBT reveal such subtleties? I know that I don't know.

I will tell you this, musicians claim they hear subtle differences in instruments that I for one have trouble hearing. Look at the world of violins. I'll be honest, I can't hear the difference between a Stradivarius and a high quality modern instrument when a violinist is actually playing music I enjoy. My wife plays the drums, and her preferred brand, DW, has three different product lines of high-end drums. Collector, Jazz, and Classic. If you go to the DW web site and read the claimed differences between these product lines it does sound an awful lot like audiophile hyperbole. Or wine tasting. My wife owns kits from two of the three product lines, and she's on a hunt to get a kit from the third, and I'll admit I don't think I could tell the difference between the snares from the different kits blind-folded. Of course, she thinks the differences are substantial enough that she even has a stainless steel snare, for when the need arises. (Don't ask me what that is.)

So if the musicians who are making the music we are so obsessed with reproducing are convinced of these subtleties, it is possible that amps are similarly differentiated? Personally, I think not. I think the differences between musical instruments, even between individual instruments from the same brand's product lines, are probably more than 40db greater than the differences between amplifiers. I suppose my point is only that the sources of our music are obsessed with subtle differences, so dismissing that humans can hear subtlety of this sort might be short-sighted.

 

[3db]

I hear you. The problem of gauging subtlety and its audibility is difficult. For example, do Pass Labs amps really sound different because Nelson has apparently figured out how to get the vast majority of distortion to be second or third harmonics, while most other amps have greater proportions of high order distortions? At -65db or less? Could a DBT reveal such subtleties? I know that I don't know.

I will tell you this, musicians claim they hear subtle differences in instruments that I for one have trouble hearing. Look at the world of violins. I'll be honest, I can't hear the difference between a Stradivarius and a high quality modern instrument when a violinist is actually playing music I enjoy. My wife plays the drums, and her preferred brand, DW, has three different product lines of high-end drums. Performance, Jazz, and Classic. If you go to the DW web site and read the claimed differences between these product lines it does sound an awful lot like audiophile hyperbole. Or wine tasting. My wife owns kits from two of the three product lines, and she's on a hunt to get a kit from the third, and I'll admit I don't think I could tell the difference between the snares from the different kits blind-folded. Of course, she thinks the differences are substantial enough that she even has a stainless steel snare, for when the need arises. (Don't ask me what that is.)

So if the musicians who are making the music we are so obsessed with reproducing are convinced of these subtleties, it is possible that amps are similarly differentiated? Personally, I think not. I think the differences between musical instruments, even between individual instruments from the same brand's product lines, are probably more than 40db greater than the differences between amplifiers. I suppose my point is only that the sources of our music are obsessed with subtle differences, so dismissing that humans can hear subtlety of this sort might be short-sighted.

As an EE I'm of teh belief that all sound no matter how subtle can be described mathematically and can be reproduced faithfully. That's why I'm suggesting that a correaltion needs to be made between specs and sound. If there's a subtle difference, what spec or combination of specs is responsible for this.

 

[Irvrobinson]

As a person that has designed audio amplifiers and have been reviewing them for over a decade that is NOT a sentiment that I share. Even at low power levels audible differences can be heard between amplifiers if the loudspeaker is revealing enough and the load is difficult. This is especially true at bass frequencies from my findings.

Yes, I know, and I actually appreciate the fact that you've come out and said it. The all-amps-sound-the-same camp, led perhaps by Peter Aczel, claim that someone like yourself could not really believe there are differences, that you would just know that all amps basically sound alike by simple comparison. So having someone like yourself, who does understand the technology, and who does reviewing, and does not from what I can see have an ax to grind, brings an important perspective to the table.

As you may have noticed, I'm somewhere on the same page you are, though you may be more at the top and me more at the bottom of that page.

 

[GranteedEV]

Not 100% pertinent, but here's some interesting comparisions:

http://www.ethanwiner.com/aes/

The artifact audibility one, uses a much more decorrelated noise than simple harmonic distortion. The Level drops by about 5 or 10 db each time. When are you unable to hear the artifacts? I found myself struggling at -55db and it was totally inaudible by -75db.
The Null tests are also interesting. How can you hear a difference, if you can't even hear "only" the difference?

 

[AcuDefTechGuy]

I hear you. The problem of gauging subtlety and its audibility is difficult. For example, do Pass Labs amps really sound different because Nelson has apparently figured out how to get the vast majority of distortion to be second or third harmonics, while most other amps have greater proportions of high order distortions? At -65db or less? Could a DBT reveal such subtleties? I know that I don't know.

I will tell you this, musicians claim they hear subtle differences in instruments that I for one have trouble hearing. Look at the world of violins. I'll be honest, I can't hear the difference between a Stradivarius and a high quality modern instrument when a violinist is actually playing music I enjoy. My wife plays the drums, and her preferred brand, DW, has three different product lines of high-end drums. Colletor, Jazz, and Classic. If you go to the DW web site and read the claimed differences between these product lines it does sound an awful lot like audiophile hyperbole. Or wine tasting. My wife owns kits from two of the three product lines, and she's on a hunt to get a kit from the third, and I'll admit I don't think I could tell the difference between the snares from the different kits blind-folded. Of course, she thinks the differences are substantial enough that she even has a stainless steel snare, for when the need arises. (Don't ask me what that is.)

So if the musicians who are making the music we are so obsessed with reproducing are convinced of these subtleties, it is possible that amps are similarly differentiated? Personally, I think not. I think the differences between musical instruments, even between individual instruments from the same brand's product lines, are probably more than 40db greater than the differences between amplifiers. I suppose my point is only that the sources of our music are obsessed with subtle differences, so dismissing that humans can hear subtlety of this sort might be short-sighted.

I think musicians and everyone else are all prone to bias.

Unless they can prove it, like in a proper DBT.

But who knows all? I can only make educated guesses based on my own experience, which may be different than everyone else.

Bottom line, if you can tell the difference and willing to pay, buy it.

The rest of us can save our money for other things in life.

 

[Irvrobinson]

As an EE I'm of teh belief that all sound no matter how subtle can be described mathematically and can be reproduced faithfully. That's why I'm suggesting that a correaltion needs to be made between specs and sound. If there's a subtle difference, what spec or combination of specs is responsible for this.

I believe that too, but I can't definitively answer your question.

 

[gene]

But a difficult load is taxing an amplifier's capability. That I can understand. But what about the comment that was made about the PassLab sounding more forward and the Classe more layed back? Those sound like midrange and treble characteristics which should present no issues for the calibre of these units mentioned. The break-in comment has me perplexed. Like I mentioned previously, maybe a coorelation of how specs affect sound would be a good thing to help understand these comments.

Yes I do believe I heard differences in upper treble response but I don't have the ability to instantly switch the amps and level match them so I am relying a bit on auditory memory. I will keep testing this though.

Don't forget the amp testing is all done through resistive loads so how the amp interacts with a complex load impedance of a speaker is different.

As for break in, most of that was tongue and cheek but warm up is a different story. The amps typically should be warmed up 10-15 min so that all of the circuits are properly biased. The nice thing about the Classe is it maintains a very constant temp at any power level ensuring consistent sound.

 

[gene]

As an EE I'm of teh belief that all sound no matter how subtle can be described mathematically and can be reproduced faithfully. That's why I'm suggesting that a correaltion needs to be made between specs and sound. If there's a subtle difference, what spec or combination of specs is responsible for this.

You will NEVER get 100% correlation between measurements and perceived differences in anything. I use measurements to flesh out product design faults NOT necessarily to declare product superiority.

Loudspeakers for example are too complex to sum up and correlate how they will sound in different listening environments with just a handful of frequency response measurements. Most of what can be measured doesn't always matter and most of what can be heard isn't always measurable.

 

[3db]

Yes I do believe I heard differences in upper treble response but I don't have the ability to instantly switch the amps and level match them so I am relying a bit on auditory memory. I will keep testing this though.

Don't forget the amp testing is all done through resistive loads so how the amp interacts with a complex load impedance of a speaker is different.

As for break in, most of that was tongue and cheek but warm up is a different story. The amps typically should be warmed up 10-15 min so that all of the circuits are properly biased. The nice thing about the Classe is it maintains a very constant temp at any power level ensuring consistent sound.

Now if Classe could only knock off 4 grand off the price of this unit..

 

[3db]

You will NEVER get 100% correlation between measurements and perceived differences in anything. I use measurements to flesh out product design faults NOT necessarily to declare product superiority.

Loudspeakers for example are too complex to sum up and correlate how they will sound in different listening environments with just a handful of frequency response measurements. Most of what can be measured doesn't always matter and most of what can be heard isn't always measurable.

Well if its subtle, maybe even where and how one sits during the tests will influence what one hears. More equations are needed!!

 

[Steve81]

Don't forget the amp testing is all done through resistive loads so how the amp interacts with a complex load impedance of a speaker is different.

That's one thing I liked about the Audio Critic using the Power Cube.

 

[Steve81]

Most of what can be measured doesn't always matter and most of what can be heard isn't always measurable.

On the other hand, for the purposes of this thread, we're not trying to measure the sound reproduced by a loudspeaker and trying to correlate it with what we hear. We're measuring electrical output of an amplifier, and on the face of it, that seems like a much easier task. Either the output matches the input plus gain or it doesn't.

 

[gene]

On the other hand, for the purposes of this thread, we're not trying to measure the sound reproduced by a loudspeaker and trying to correlate it with what we hear. We're measuring electrical output of an amplifier, and on the face of it, that seems like a much easier task. Either the output matches the input plus gain or it doesn't.

It's not always that cut and dry. You measure a worst case test signal with a best case test load vs listening to a worst case load on a dynamic and usually less strenuous signal. Measurements do tell a lot but you can't rely solely on them 100% for audio electronics let alone loudspeakers.

 

[GranteedEV]

It's not always that cut and dry. You measure a worst case test signal with a best case test load vs listening to a worst case load on a dynamic and usually less strenuous signal. Measurements do tell a lot but you can't rely solely on them 100% for audio electronics let alone loudspeakers.

Um..... why exactly can't you measure a worst case test load?

It sounds to me a classic case of "The measurements are incomplete therefore the listening is more relevant"

But for electronics I'm not sure that should ever be the case given the dubious nature of the industry. The measurements should always be weighed greater. If that means measuring into a 1 ohm load @ 75 degree phase angle for a $5000 amp @ 10hz to 22khz, I don't see why not. It's pretty insane but the measurements should always represent a worst case scenario not a middle of the road scenario.

Likewise with loudspeaker measurements. Why only measure 30 degrees off axis when the sound at 60 or 70 or even 150 degrees off axis has been shown to affect perception?

I understand as a reviewer time constraints etc come into the picture but it's unfair to do half-measurements - and then claim that they don't help identify what you heard.

I'm not criticizing your measurements here Gene. They're great and appreciated as are the subjective commentary. But It's a bit disheartening to see you post the measurements and then claim they're inadequate relative to your experience. If your own speakers are a more complex load than the test signal, then as pretty much the publication leader we expect you to address that objectively rather than use the limitations of the measurements as evidence. I don't really like the idea that something that can be heard but can't be measured. That's awful close to "cable" territory to me. It can either be measured or you choose not to/lack the capability to measure it.

Sorry to rant especially since this was a really good review but your comment that you can hear things that you can't measure just doesn't sit well with me. I'll admit my measurement capability compared to yours is infinitesmal but I also don't make such claims. I know you know this but it feels you just word things in a certain way that gives teh wrong impression.

It seems like a very good topic for an AH article - what aspects of amplifiers when isolated - are actually audible in an ABX / single blind test? I have no doubt that if you can hear it, you can measure it but complexity is the keyword.

 

[Steve81]

It's not always that cut and dry. You measure a worst case test signal with a best case test load vs listening to a worst case load on a dynamic and usually less strenuous signal. Measurements do tell a lot but you can't rely solely on them 100% for audio electronics let alone loudspeakers.

I agree to a certain extent. I'd contend that measurements of an amplifier *could* tell you everything you needed to know about it, but the reality is, nobody is measuring an amplifier that thoroughly. I mean, even the aforementioned power cube test is limited; yes, you can see that the amplifier delivers power into complex loads at 1kHz, but you're not seeing the distortion profile, how it performs in terms of frequency response into those loads, etc.

As a side note, that's one thing I can appreciate about THX certifications, ie they address both sides of the equation, the loudspeaker and the amplifier to ensure they work together.

 

[panteragstk]

Here is my take on the audibility of differences in amps. Any of you guys play guitar (not acoustic)? EVERY guitar player I know (lots) love their tube amps over the solid state amps. They claim all kinds of things about the difference in sound. Not scientific, but interesting.

Having tested a multitude of amps for pro audio (never had the opportunity to do it in the consumer world) I can tell you that amps with a specific wattage rating (not always what they are actually capable of) but are either different class of amp or different manufacturer do sound different when used on the same speaker. Being an almost EE (haven't graduated) I understand why you guys want to quantify what Gene is saying.

Here is what I think based on my experience: Gene stated in the article that in the bass region that it is pretty easy to see what amps can handle difficult loads. I've seen this numerous times in the pro audio world. We take a low end QSC gx series amp and put it to a 4ohm nominal dual 18 sub and blast 120db out of it with frequencies going down to 20hz or below. I would imagine the ohm load goes pretty low at some point. The reason I know (think) this is because a newer drivecore amp from crown produced those frequencies MUCH easier than the qsc rated at the same power output, but the QSC isn't rated for 2ohm performance, so when the ohm load drops it has issues (what I think is happening). Most of you are already aware of this, lower ohm loads are difficult for some amps.

For the difference Gene heard in the higher frequencies why can't the same be true? At higher frequencies the ohm load presented to the amp may be something it doesn't handle the same way as another amp, so wouldn't that make an audible difference? Couldn't that explain why some people think some amps sound different in the upper frequency range than others? Or am I just blowing smoke out my ***?

 

[panteragstk]

But for electronics I'm not sure that should ever be the case given the dubious nature of the industry. The measurements should always be weighed greater. If that means measuring into a 1 ohm load @ 75 degree phase angle for a $5000 amp @ 10hz to 22khz, I don't see why not. It's pretty insane but the measurements should always represent a worst case scenario not a middle of the road scenario.

That would answer the question I posted above. I don't think I've ever seen someone measure an amp in that way in any review ever. I don't think most could handle that.

 

[GranteedEV]

That would answer the question I posted above. I don't think I've ever seen someone measure an amp in that way in any review ever. I don't think most could handle that.

Of course not. But I don't think most could handle Gene's speakers either.

Likewise, what if my speakers were some perfect 95db/w/m, 8 ohm +/- 2 ohm where theta is +/- 30 degree. if there are multiple drivers they are each driven by their own amplifier not in parallel. ...then I don't hear the difference gene heard. What do you draw from that?

I'm just trying to figure it out. It feels to me that the real world scenario should never be a worse one than the testing scenario. And a resistive 4 ohm load is likely an easier one than a 2 ohm, 50 degree phase angle scenario like whatever Gene mentioned in the review. There should definitely be a double standard. Obviously if an amp is struggling with the basic scenario then the tough scenario is out of the question - for both measurement and ALSO listening. But for a $5000 like this Classe, it's pretty much ::expected:: to drive ultimate speakers IE Apogee or the status acoustics.

 

[gene]

Um..... why exactly can't you measure a worst case test load?

It sounds to me a classic case of "The measurements are incomplete therefore the listening is more relevant"

But for electronics I'm not sure that should ever be the case given the dubious nature of the industry. The measurements should always be weighed greater. If that means measuring into a 1 ohm load @ 75 degree phase angle for a $5000 amp @ 10hz to 22khz, I don't see why not. It's pretty insane but the measurements should always represent a worst case scenario not a middle of the road scenario.

Likewise with loudspeaker measurements. Why only measure 30 degrees off axis when the sound at 60 or 70 or even 150 degrees off axis has been shown to affect perception?

I understand as a reviewer time constraints etc come into the picture but it's unfair to do half-measurements - and then claim that they don't help identify what you heard.

I'm not criticizing your measurements here Gene. They're great and appreciated as are the subjective commentary. But It's a bit disheartening to see you post the measurements and then claim they're inadequate relative to your experience. If your own speakers are a more complex load than the test signal, then as pretty much the publication leader we expect you to address that objectively rather than use the limitations of the measurements as evidence. I don't really like the idea that something that can be heard but can't be measured. That's awful close to "cable" territory to me. It can either be measured or you choose not to/lack the capability to measure it.

Sorry to rant especially since this was a really good review but your comment that you can hear things that you can't measure just doesn't sit well with me. I'll admit my measurement capability compared to yours is infinitesmal but I also don't make such claims. I know you know this but it feels you just word things in a certain way that gives teh wrong impression.

It seems like a very good topic for an AH article - what aspects of amplifiers when isolated - are actually audible in an ABX / single blind test? I have no doubt that if you can hear it, you can measure it but complexity is the keyword.

I spent many years thinking everything in audio could neatly be measured and quantified. If fact I am pretty anal retentive about this beyond just audio but I am slowly realizing that we don't always get the whole picture from text book measurements & analysis.

This is a good topic for an article that I plan on writing when I find the time.

I do the most exhaustive testing in amplifiers that I've seen compared to any publication. I've even spoken with the folks at Audio Precision and they were impressed with my methods. I am still not 100% happy however as I'd like to do more but as you pointed out, my time is limited and I am the only person on staff that does amplifier measurements for Audioholics.

Distortion audibility is a complex topic one that the folks at AP also discussed at our 2008 SOTU event in this rather boring but interesting video:

Audio Precision Amplifier Testing Methods Class — Reviews and News from Audioholics

Again sometimes text book theory doesn't always apply to real world. I found this especially true with loudspeakers and somewhat applicable to amplification.

 

[gene]

I agree to a certain extent. I'd contend that measurements of an amplifier *could* tell you everything you needed to know about it, but the reality is, nobody is measuring an amplifier that thoroughly. I mean, even the aforementioned power cube test is limited; yes, you can see that the amplifier delivers power into complex loads at 1kHz, but you're not seeing the distortion profile, how it performs in terms of frequency response into those loads, etc.

As a side note, that's one thing I can appreciate about THX certifications, ie they address both sides of the equation, the loudspeaker and the amplifier to ensure they work together.

Agreed which is one of the reasons power cube testing really doesn't interest me and hence why so few people even use them. I am trying to get Emotiva to build me a complex load impedance bank so if enough people here chew them out for not building it for me yet, it may happen

THX is great for interoperability but their testing on amps, and especially subs is rather anemic. Our Bassaholic certification is far more stringent than their Ultra2 or Big Room spec. Their amp testing mostly deals with dynamic testing which is how a $1k receiver can easily meet their Ultra2 requirement.