Classe CT-2300 Stereo Power Amplifier Review

[3db]

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.

IHO as an engineer, even subtle differences have equations behind them and there are measurements or a combination of measurements that will correlate to how an amplifier sounds. I firmly believe this. Maybe its never been done before to that extent but I think it should be. That way audiophiles and people selling snake oil ( not implying anything to you ) can be held accountable for the travesties in this industry.

Speakers are different from amps only from the perspective of room interaction espcially with respect to seating position. There are too many variables in/for a room to even think that measurements would describe accurately how a speaker sounds. I realize that even mic placement can alter the measurements of a speaker. Its far more complicated from a variables point of view than amps that for sure. If one had a thousand years, maybe one could accurately model speaker interaction with its room.

I look forward to the article. It may change my opinion on amp's sonic signatures

 

[Steve81]

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

Crafting e-mail to Emo, check

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.

Well you know their argument about receivers and burst testing, ie it tends to be more representative of a real world program material than say, ACD continuously. Since I don't use THX speakers though, the main use I had for the certification on my receiver was that it confirmed the receiver could handle speakers dipping down to 4 ohms on the front channels; at the time I got my TX-SR707, I was only running a 2.1, so that was good enough.

As far as subwoofers go, I wouldn't mind hearing a Klipsch Ultra setup in an appropriate room, but I'm quite happy with my new Bassaholic Extreme certified SVS Ultra

 

[Josuah]

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"

There isn't one worst case test load. The result of the interaction between the load and the signal will be different for different loads, and that will change the sound but not necessarily in a "worst case" scenario where everything other than the worst case is still OK.

There are lot of measurements we don't do, including output phase, decay, individual frequency response as a function of the load impedance and phase (that'd be one strange looking multi-dimensional graph), steady-state multi-tone distortion, dynamic multi-tone distortion (maybe different than steady-state?), the specific distortion plots for various test signals (since the single number value could be the same but computed from different values), etc.

What's perhaps the best measurement? Maybe an ADC capture of a complicated musical passage that is directly compared to the digital analysis of the original sound file. (I kind of did this, looking at oscilloscope traces to see how they differed depending on what I was hearing. A sort of confirmation in the other direction.)

The truth of the matter is our brain and ears are extremely sensitive acoustic mass-measurement devices. For that reason, listening can be more relevant. Much in the same way our brain and eyes are extremely good at fast visual pattern recognition and computers still aren't anywhere close.

There should be a measurement difference to match differences in what you hear. But most of the time you don't know what to look (measure) for until you find a reason to. Kind of like a blind person measuring photon intensity but never thinking to measure wavelength.

 

[RichB]

Have you asked ATI to send AH an AT3007 amp yet?

Anyone has a Mark Levinson amp so we can compare?

any votes for an ATI Signature Series.

- Rich

 

[RichB]

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.

Thanks for the link to this excellent video. A must watch.
Some interesting points include the nature of distortion, the masking and tolerance to clipping distortion, the level at which distortion is measured, it goes on.

One Web Site note: It may be my IE, but I could not index into the video after accidentally closing the browser.

- Rich

 

[AcuDefTechGuy]

any votes for an ATI Signature Series.

- Rich

The ATI Signature 300W x 7Ch Amp is $8K MSRP. Let's say I could get for $5K. I can get the $10K MSRP Lexicon 300WPC x 7Ch for $4K (b-stock, full warranty). So no vote for the ATI Signature amp from me.

http://www.hometheaterhifi.com/power-amplifiers/power-amplifiers-reviews/a-secrets-power-amplifier-review12.html

 

[RichB]

The ATI Signature 300W x 7Ch Amp is $8K MSRP. Let's say I could get for $5K. I can get the $10K MSRP Lexicon 300WPC x 7Ch for $4K (b-stock, full warranty). So no vote for the ATI Signature amp from me.

Lexicon ZX-7 Multi-Channel (300 watts x 7) Power Amplifier - Secrets of Home Theater and High Fidelity

There are aspects of the ATI signature that are interesting and represent ATI's newest design and best efforts.
For $1K and that reason alone, buying blind, I would go for the Signature.

Your a great ATI customer, maybe they will let you try one...
Have you seen the new beefier handles...

- Rich

 

[AcuDefTechGuy]

There are aspects of the ATI signature that are interesting and represent ATI's newest design and best efforts.
For $1K and that reason alone, buying blind, I would go for the Signature.

Your a great ATI customer, maybe they will let you try one...
Have you seen the new beefier handles...

- Rich

No I just now noticed those bigger handles. And I forgot that Lexicon (also Mark Levinson) does NOT have any front handles. So I guess I will have to give the edge to the ATI.

 

[Adam]

I wonder if Josuah was crafting that response for the past 18 months.

 

[AcuDefTechGuy]

The truth of the matter is our brain and ears are extremely sensitive acoustic mass-measurement devices.

Yes. Our brains and ears are very sensitive to the 1dB+ difference in sound level.

 

[3db]

Yes. Our brains and ears are very sensitive to the 1dB+ difference in sound level.

That's only partially true. It depends where in the frequency band that the change occurs. We are most sensiitve to a fairly narrow band between 1.5K to around 3K. Anything outside that envelope and our sensitivity drops off.

 

[AcuDefTechGuy]

That's only partially true. It depends where in the frequency band that the change occurs. We are most sensiitve to a fairly narrow band between 1.5K to around 3K. Anything outside that envelope and our sensitivity drops off.

So you won't notice a 6dB difference in sound level at 3.5kHz?

 

[3db]

So you won't notice a 6dB difference in sound level at 3.5kHz?

(

What I'm saying is our hearing senstivity is most accute in a narrow frequency band (Fletcher Munson curves I believe they are called) so we can detect 1db differences in that narrow frequency band.... Move towards the frequency limit of our hearing....40Hz and 14Khz as an example and we humans would not be able to detect a 1db increase/decrease.

Some useless trivia.. if we could hear the echo location used by bats, we would suffer instant permanent hearing loss as they chirp in excess of 120db....

 

[Josuah]

I wonder if Josuah was crafting that response for the past 18 months.

I still read the articles but only poked into the forum because the bottom of the review page had some comments that looked interesting.

 

[gene]

Thanks for the link to this excellent video. A must watch.
Some interesting points include the nature of distortion, the masking and tolerance to clipping distortion, the level at which distortion is measured, it goes on.

One Web Site note: It may be my IE, but I could not index into the video after accidentally closing the browser.

- Rich

That video is ancient as it was before we started hosting them on Youtube. Sorry about that.

 

[PENG]

I think what the previous poster is saying is that because its made in China where labor is dirt cheap, a price drop should be expected but its not the case. I happen to concur with him. Even though Classe is a Canadian company, I would expect the price to be cheaper now that its being built in China. $3000 per channel sounds very expensive.

Regardless of whether that's what the previous poster was trying to say, I thought you hit the nail on the head. If Bryston starts making the 4B SST2 in China and drop the price by $2,000, I may consider trading my SST in, otherwise I would just get another made in Taiwan A21 for half the price.

 

[PENG]

Yes. Our brains and ears are very sensitive to the 1dB+ difference in sound level.

I think he needs to learn more about Placebo, factor that in, and try to measure that too.

 

[PENG]

(

What I'm saying is our hearing senstivity is most accute in a narrow frequency band (Fletcher Munson curves I believe they are called) so we can detect 1db differences in that narrow frequency band.... Move towards the frequency limit of our hearing....40Hz and 14Khz as an example and we humans would not be able to detect a 1db increase/decrease.

Some useless trivia.. if we could hear the echo location used by bats, we would suffer instant permanent hearing loss as they chirp in excess of 120db....

I actually agree with you, that's why I put a lot of weight on DBT, or at least SBT. I just don't think ST is all that trustworthy.

 

[RichB]

I actually agree with you, that's why I put a lot of weight on DBT, or at least SBT. I just don't think ST is all that trustworthy.

When my amp is distorting, I do not reach for a panel of experts and a blindfold

These difference are not always subtle.

Edit: Just having some fun

- Rich

 

[RichB]

^
I think it is important to qualify what amps are being compared.
Bryston, Parasound, ATI amps or a $500 receiver and what are your driving and how hard.

- Rich