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Classe CT-2300 Two-Channel Amplifier Measurements and Analysis

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All measurements were conducted using our Audio Precision APx585 8 Channel HDMI Audio Analyzer following our rigid Amplifier Measurement Test Protocol.

I did some quick spot-checking on the CT-2300 amplifier gain structure to ensure it could be properly driven with a wide assortment of preamps or receivers. My personal criteria for amplifier gain structure is that it should be able to hit full power when driven with 2Vrms which the CT-2300 met just fine clipping at about 1.9Vrms. I measured 29dB gain with an 8 ohm load attached which is what Classe specs this amp to be.

Signal to Noise Ratio

CT2300-SNRa-1watt.jpg

Classe CT-2300 SNR @ 1 watt (A-weighted)

The CT-2300 exhibited a very good low noise floor. At 1 watt I measured 94dB (A-weighted) and 92dB with only a 20kHz filter engaged. The small improvement with A-wt filtering engaged indicated this amp exhibited a very low out of band residual noise. At rated power, I measured 117dB which is slightly better than Classe specs the CT-2300 at.

Frequency Response

 CT2300-Freq-fullpwr.jpg

Classe CT-2300 Frequency Response @ Full Rated Power

The Classe CT-2300 exhibited ruler flat bandwidth from 10Hz to 30kHz with a gradual roll-off of about -1dB at 50kHz and about -3dB at 80kHz which is what Classe specs this amp at. Frequency response linearity between both channels at 1 watt and full power was +-0.1dB for the entire audio band which was excellent. This indicates very tight tolerances in parts selection and excellent overall engineering.

Power Measurements

Using our Audio Precision APx585 8-channel HDMI analyzer, I conducted a full barrage of multi-channel amplifier tests on the Classe CT-2300. We tested power using three methods all of which were taken at < 0.1% THD + N:

  • Continuous Full Power Bandwidth (CFP-BW) from 20Hz to 20Khz into 8 and 4-ohm loads (up to two-channels)

  • 1kHz Power Sweep vs Distortion (1kHz PSweep) - popularized by the print magazines, this is an instantaneous power vs distortion test at 1kHz. The problem with this test is it often masks slew related and or frequency response problems some amplifiers exhibit at the frequency extremes, and thus inflates the measured power results. It does provide an instant gratification # for consumers to argue over on the forums so we are now incorporating this test to please the masses.

  • Dynamic PWR - 1kHz CEA-2006 Burst Method testing. This is a dynamic power measurement adopted from the car industry similar to IHF method only a bit more difficult for an amplifier and more representative of real musical content.

Keep in mind most review publications don't do continuous power measurements and they usually publish power measurements into clipping at 1% THD + N. Our measurements are very conservative as we use a dedicated 20A line with no Variac to regulate line voltage. We constantly monitor the line to ensure it never drops more than 2Vrms from nominal which in our case was 120Vrms.

For more info on amplifier measurements, see: The All Channels Driven (ACD) Test

CT2300-1ksweep-8ohm.jpg 

CT2300-1ksweep-4ohm.jpg 

Classe CT-2300 1kHz Power Test
Top Pic: 2CH driven, 8 ohms; Bottom Pic: 2CH driven, 4 ohms

CT2300-dynamicPWR-8ohm.jpg

CT2300-dynamicPWR-4ohm.jpg

Classe CT-2300 Dynamic Power Test (1kHz)
Top Pic: 2CH driven, 8 ohms; Bottom Pic: 2CH driven, 4 ohms

 

# of CH Test Type Power Load THD + N
1 CFP-BW 360 watts 8 ohms 0.1%
2 CFP-BW 340 watts 8 ohms 0.1%
1 CFP-BW 670 watts 4 ohms 0.1%
1 CFP-BW 700 watts 4 ohms 1%
2 CFP-BW 590 watts 4 ohms 0.1%
2 CFP-BW 610 watts 4 ohms 1%
2 1kHz Psweep 344 watts 8 ohms 0.1%
2 1kHz Psweep 357 watts 8 ohms 1%
2 1kHz Psweep 590 watts 4 ohms 0.1%
2 1kHz Psweep 610 watts 4 ohms 1%
2 Dynamic PWR 394 watts 8 ohms 1%
2 Dynamic PWR 767 watts 4 ohms 1%

                   Classe CT-2300 Power Measurement Table

Classe rates the CT-2300 as follows:

  • 300 watts x 2 continuous @ 8-ohm

  • 600 watts x 2 continuous @ 4-ohm

Classe doesn't specify at what frequency they rate their power output, but I assume they mean 1kHz which is how most manufacturers specify all channels driven power claims. They also don’t specify the power level or test conditions the specified distortion of 0.002% was conducted at.

The amp protection circuits shut down the CT-2300 when sweeping at full power (2CH driven) starting at 10Hz, but was fine when I raised the start frequency to 20Hz. This is something that would never happen in real world usage. It’s a smart idea to build in protection like this to increase longevity and reduce failures when reviewers (like myself) attempt to break products during our bench testing.

My measurements revealed that the CT-2300 is a true powerhouse and lives up to the published power figures Classe specified for this amplifier. Since we don’t use a Variac to hold line condition constant, it’s very difficult to get accurate distortion measurements at full rated power. Although the amp was showing 1% distortion driven at full power into 4 ohms, the analog waveform was still very smooth and unclipped.

The CT-2300 produced virtually identical full power bandwidth and 1kHz power sweep tests indicating that the power supply and output devices were robust enough to deliver full rated power at any audio frequency, not just a sweet spot. This is just one of many hallmarks indicating the CT-2300 is a seriously great amplifier. The dynamic power results were likely limited by the wall current of my test setup. I suspect under ideal test conditions, the CT-2300 would have more available dynamic power. At these power levels, who cares? The CT-2300 could drive virtually any speaker load. I didn’t need these test results to be convinced after just a few short listening sessions powering my new Status Acoustics 8T reference speakers.

FFT Distortion Analysis

CT2300-FFT-1watt.jpg

CT2300-FFT-Fullpwr.jpg

Classe CT-2300 FFT Distortion Analysis
(Top pic: @ 1 watt ; Bottom pic: @ full power)

I ran FFT distortion plots at 1 watt (top pic) and full rated power (bottom pic) to determine how clean this amplifier really is. At 1 watt, the spectral distortion was below the noise floor of my measurement equipment which is another way of saying “awesome”!

At 316 watt, I observed the 3rd harmonic (34.032 + 51.67)dBV being 85.7dB down from the fundamental or 100*alog^-1(-74.1/20) = .0052% The odd order harmonics start dominating as the amp starts hitting the rails and becoming slew rate limited at very high frequencies. This is really a great result and shows how over designed this amplifier really is. When I lowered the power level to 300 watts (rated power) the 3rd harmonic dropped and the FFT looked excellent; perhaps one of the best results we’ve seen from any amplifier to grace our test bench.

Crosstalk

The sweep tests I ran on the CT-2300 produced excellent results, but I am sad to say the file got corrupted so I cannot post an image here. Luckily I wrote down the data at various frequency points as follows:

20Hz to 1kHz: > 100dB

20kHz: > 90dB

I consider anything less than -40dB @ 10kHz acceptable and anything less than -80dB to be superb so the CT-2300 met that minimum requirement with over 10dB to spare and at 20kHz no less. I reran these results at 100 watts and near full rated power and achieved similarly excellent figures. Classe did their homework with respect to board layout and component isolation to ensure minimal crosstalk which also assures excellent stereo separation.

Recommendations

Classe InstallBecause of the large power capacitance reserve bank, powering up the CT-2300 produces a large inrush current transient that may cause your lights to momentarily dim if you’re not running it on a dedicated line. I recommend connecting the CT-2300 to a dedicated 15A or 20A line so you can take full advantage of the power this amplifier offers. I’d also recommend plugging this amplifier directly into the wall as most power conditioners could potentially rob this amplifier of power and also needlessly strain during turn on cycles. If you plan on installing this amplifier into an equipment rack, the supplied rack rails could be useful but I’d advise the installer to see what works best for the particular installation. Always follow the manufacturer’s installation instructions carefully when placing this amplifier into a rack to prevent damage or personal injury. Although you can stack these amps, I’d still recommend giving a few inches of ventilation at the top with plenty of back air flow so the ICTunnel can function properly.

It is important to note that with the faceplate installed, the CT-2300 won’t flush mount to your rack like other component gear often does. While there is nothing wrong with that, it may look a bit odd like it does in my case having one of your components in your rack protrude while the others do not. It also makes it easier for an envious audiophile friend to pull a heist on you when you’re not looking so watch out.

If you’re planning on installing this amplifier on a shelf or floor mounting it, I’d suggest considering spending the extra $500 for the CA-2300 version. An amp that performs this good deserves to flaunt its stuff in fancy clothing.

 

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Recent Forum Posts:

AcuDefTechGuy posts on March 13, 2014 10:27
RichB, post: 1022651
any votes for an ATI Signature Series.

- Rich

I assumed that ATI was the better value, but perhaps I may be wrong. Parasound Halo might be the better value. I will have to look into that.

I mean if you could get the Parasound Halo A21 250WPC amp brand new for a few hundred dollars less than the ATI AT2002 200WPC amp, I don't know if I can recommend the ATI.
RichB posts on March 12, 2014 21:09
PENG, post: 1022880
I feel the same way in that regard. For me, when I say amps sound the same I always meant mid range to high end class A, A/AB and AB amps in perfect condition and operating within their specified limits with adequate headrooms. I would not expect an Outlaw monblock m2200 or an Emo upa-200 sound the same as any classe monoblocks. They may, but I just would not expect them to and would not believe it, not until I have heard them side by side in a blind test.

I am on the same page. I never don't worry about was about small levels of distortion.

I suspect some amps produce less harmonics played at low levels and that may matter if you have a system/room capable of resolving them.

Some amps may handle complex loud better than others.
Dynamic content can have greater demands than you can account for.
It is not easy to determine how much power is needed for a given system and I suspect we are pretty tolerant to clipping.

Well made A/B amps are more alike the different.
There are certainly better places to put money than some of these rarified amps.

- Rich
PENG posts on March 12, 2014 21:03
RichB, post: 1022876
I know why.

I guess I will never experience that final bit of control, heft, and air.

I think sometimes it is unclear that if we are discussing $400 receivers versus ATI 3000's or
Pass Labs and Parasound.

- Rich

Of course, I totally forgot the heft and air lol!!
PENG posts on March 12, 2014 21:02
RichB, post: 1022876
I know why.

I guess I will never experience that final bit of control, heft, and air.

I think sometimes it is unclear that if we are discussing $400 receivers versus ATI 3000's or
Pass Labs and Parasound.

- Rich

I feel the same way in that regard. For me, when I say amps sound the same I always meant mid range to high end class A, A/AB and AB amps in perfect condition and operating within their specified limits with adequate headrooms. I would not expect an Outlaw monblock m2200 or an Emo upa-200 sound the same as any classe monoblocks. They may, but I just would not expect them to and would not believe it, not until I have heard them side by side in a blind test.
RichB posts on March 12, 2014 20:53
PENG, post: 1022875
They all distort but differently in many forms. My point is, when blindfold most people couldn't tell those distortions (0.05, 0.001, or 0.0001% of any distortions) apart.

How many times have you read a professional review that claims a $2000 amp such as the A21 that sounds as good or better than a $100,000 Boulder, Goldmund, or even the lower high end in the $10,000 range from McIntosh, Krell, Conrad Johnson, Pass Lab etc.? I have never come across one. Invariable they would praise the entry level high end A21 or Bryston SST2 to the nth degree and then would add something like, that is not to say it is as good as the $10,000………….., for example the $10,000 xyz amp just give you that extra bit of warmth, and that final touch of details in the highs, blablabla etc etc… Ever wonder why?

Yep I'm having fun too, fun is good.

I know why.

I guess I will never experience that final bit of control, heft, and air.

I think sometimes it is unclear that if we are discussing $400 receivers versus ATI 3000's or
Pass Labs and Parasound.

- Rich
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