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Review and Measurements of Class D Audio CDA-250C Amp

amirm

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#1
This is a review and detailed measurements of the Class D Audio (the company) CDA-250C Power (speaker) Amplifier. It is on kind loan from a member. The CDA-250C costs USD $495 from the company direct which barely sneaks it into affordable class.

There is not a whole lot to look at on the face of the unit:

Class D Audio CDA-250C Amplifier Audio Review.jpg

As you see, the unit is made in USA. I suspect the case is generic Chinese though given the DIY look and feel it has.

The power button is oddly in the right side of the unit.

The back panel sports very large speaker jacks which is nice:

Class D Audio CDA-250C Amplifier Back Panel Audio Review.jpg


Unfortunately there are no balanced inputs even though the holes seem to be made for them.

Another miss is lack of any safety or regulatory certification.

In testing, the CDA-250C ran completely cool. I could not feel slightest rise in temperature of the case whether I touched the top, left or right, which is really good.

Measurements
Let's start with our usual dashboard at 5 watts of output:

Class D Audio CDA-250C Amplifier Audio Measurements.png


I was pleased to see the unit working well enough to allow me to measure it down to DC and hence the DC offset. Many recent switching amplifiers make my analyzer go crazy if I DC couple of it.

SINAD (signal over distortion and noise) is rather low and seems to be driven by high noise floor than distortion products (which are below 100 dB).

Signal to noise ratio is disappointing:
Class D Audio CDA-250C Amplifier Signal to Noise Ratio Audio Measurements.png


We can't even clear the CD's 96 dB at either 5 watt. We barely get there with 200 watts of output (which is already pretty distorted).

The news gets pretty ugly when I measured THD+N versus frequency at six different power levels:

Class D Audio CDA-250C Amplifier Distortion versus Frequency Audio Measurements.png


We have multiple problems here. At both low and high end of the frequency spectrum we have rising noise and or distortion. The higher the power, the worse they get.

At low power outputs (around 1 to 2 watts), low frequency noise seems to escalate which may be due to power supply noise.

To top it all, two channel are wildly different than each other. One seems to be a lot more susceptible to noise than the other.

Let's look at the spectrum of 1 kHz tone with wide bandwidth and see if we can figure this out:

Class D Audio CDA-250C Amplifier 1 kHz FFT Audio Measurements.png


I should have run this without my external filter but let's run with it anyway. We see our usual spikes in hundreds of kilohertz due to switching frequencies. But we also see a rise in noise around 50 kHz or so. The previous test uses 90 kHz bandwidth so this peak will impact the measurements. Note again the channel mismatch.

Let's rerun the previous test, this time by limiting the bandwidth to 22.4 kHz. Note that this means that we can't capture anything past second harmonic for the high frequencies (hence the reason the levels artificially drop there):

Class D Audio CDA-250C Amplifier Distortion versus Frequency Audio Bandwidth Audio Measurements.png


The graph becomes somewhat cleaner especially at low output level (in red). But otherwise, the signature issues with distortion/noise remain.

Let's run our typical power versus distortion test. Note that 1 kHz tone is used for this test so doesn't incorporate the issues we see above:

Class D Audio CDA-250C Amplifier Power Audio Measurements.png


We have good bit of power reaching 178 watts into 4 ohm before clipping sets in. FYI, I have refined this test to give us more resolution near max power so it is a bit unfair to previous products I tested. Still, this is quite a bit more power than the two reference amps in the graph.

When I get a chance later, I will test the output impedance versus frequency. And a frequency response test which I just realized I forgot to run too. :)

Conclusions
Getting nearly 200 watts/channel into 4 ohm for a US made power amplifier for $500 is not bad. Outside of that, you have to close your eyes to many flaws. These noise and distortion issues way dwarf anything upstream. As such, I don't see the Class D Audio CDA-250C in any kind of high fidelity system. Our search will continue for something with Hypex NC400 performance but at half the price.

Needless to say, I can't recommend the CDA-250C but you can judge it for yourself and your application based on above data and decide.

------------
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#3
Bummer, I was looking seriously at their balanced amps. The gain trim on some of their amps was also a very attractive feature for gain staging with a variable output DAC.

I'm starting to think that we should be skeptical of any modern amps.

Fingers crossed for the Emotiva PA-1.
 

RayDunzl

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#5
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#6
I use 3 CDA-120's in my active setup right now. Honestly, they always sounded good to me, but seeing these measurements make me question if I should make a change. I

Thanks for the measurements.
 

restorer-john

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#8
Please keep reviewing these Class D atrocities Amir, you are performing a great community service.

It makes all our older and higher performing vintage amplifiers much more valuable on the 2nd hand market. :)
 

Ilkless

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#10
Conclusions
Getting nearly 200 watts/channel into 4 ohm for a US made power amplifier for $500 is not bad.
The lowest I'd go for US-made new is ATI's stuff, including what they OEM for Outlaw and Monoprice. US-made for the sake of US-made seems quite pointless when the basic performance is not up to snuff.
 

restorer-john

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#12

anmpr1

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#14
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#15
I guess the poor measurements really shouldn't have been too much of a surprise; the specs on the Class D Audio website claim a THD of "Better than .02% (normal listening is about .003%)". Assuming this is THD sans noise, Amir's THD+N results of around .009% sounds about right.

Still, this is first objective review I've seen of any of Class D Audio's amps, and I am disappointed; like Amir (and others), I was hoping this might be the breakthrough budget Class D amp that demonstrates decent performance.

I'm still holding out hope for budget ICEPower-based amps such as the Emotive PA-1, and also Hypex NC252MP-based amps such as March Audio's P252, Nord's One MP NC252 or Apollon Audio's NCMP400.
 
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#16
Emotiva PA-1 is what I would like to see. It also uses the same ICE module in the PS Audio S300, so I wonder how their performance differs (people claiming the output stage makes a world of difference).
Actually, it's the input stage that some folks (particularly PS Audio) claims makes a big difference. PS Audio touts their custom "Analog Cell" input stage as the big selling point of their S300 amplifier, supposedly differentiating it from other amplifiers using the same ICEPower 300AS1 amp modules.
 

MZKM

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#18
Actually, it's the input stage that some folks (particularly PS Audio) claims makes a big difference. PS Audio touts their custom "Analog Cell" input stage as the big selling point of their S300 amplifier, supposedly differentiating it from other amplifiers using the same ICEPower 300AS1 amp modules.
Correct, that’s for the correction.
 
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#19
Wow, this is sad! Guess who will be selling his SDS-470C in the next days
I wouldn't sell something you enjoy because it measured poorly. I use and appreciate Amir's measurements as a guide for buying and recommending new equipment, not as a guide for enjoying my existing gear. =)

These kinds of measurements are valuable from an engineering perspective, but their audibility under normal listening conditions is an open question particularly for speaker as opposed to headphones. The noise floor of a quiet room is 30-40dB, even with no music playing. And the loudspeaker and your room will add even more distortion. So you have to ask yourself if these issues are something you can hear. Or, better yet, get a hold of a better-measuring amp and do a A vs. B comparison yourself.
 
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