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Review and Measurements of Denon PMA-50 Amplifier

Willem

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#44
For units such as these the quality of the analogue input is quite irrelevant in my view. They are to be used with the digital outputs of streamers like the CCA, a television or a computer.
 
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#45
I don't get what you are saying here. This is what pretty much all amplifiers do, unless they are current-drive amps. Thus the rating of about 2X max power driving 4 ohms compared to 8 ohms.
I guess I wasn't exactly clear--I was referring to voltage equality at max power output, and along with that, THD+N equality up the voltage ladder between 8 and 4 ohm loads. Obviously any reasonably low output impedance amp will deliver double wattage when speaker impedance drops, until it hits its power limits. See the NAD C 328 and D 3020 for Class D integrated amps, and almost any AVR for A/B amps, which do not double their 8 ohm power into 4 ohm loads.
 
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#46
[Polish] https://audio.com.pl/testy/stereo/wzmacniacze-stereo/2388-denon-pma-50

to English:

* https://translate.google.com/translate?hl=&sl=auto&tl=en&u=https://audio.com.pl/testy/stereo/wzmacniacze-stereo/2388-denon-pma-50

* https://www.translatetheweb.com/?fr...y/stereo/wzmacniacze-stereo/2388-denon-pma-50

[ Denon accurately defined the PMA-50 output power. We expect 2 x 50 W at 4 ohms, and we obtained 2 x 52 W, and 2 x 26 W with twice the impedance. The same power is obtained when driving a single terminal.

Due to the presence of protection circuits that limit the voltage at the output (to avoid high distortion), the measurements do not refer to the usual THD + N = 1%, but just to the level at which the protection is activated.



Sensitivity for analog inputs is close to 0.17 V. The noise level is already severe (at least in the measurements, it is high frequency noise, so their impact on the sound is indirect), the S / N ratio is only 63 dB, and the dynamics barely 77 dB... ]

Ejem...

That website tends to measure more noise than other sources. See the Denon AVR-X5200W at audio.com.pl and at Sound and Vision, the Anthem STR at audio.com.pl and at Stereophile, and the Yamaha A-S801 at audio.com.pl and at Audioholics. Audio.com.pl are the ones out of step with everyone else on noise figures, not @amirm , so I would look to them for answers. I've got no explanation but many entirely unsubstantiated guesses: most amps filter 60hz+H noise better than 50hz+H noise, European models have some additional circuitry that generates noise, audio.com.pl has a noisier signal chain, or audio.com.pl has noisier power at their testing location or is located near some other noise-generating source.
 

maty

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#47
Interesting observation, Watson. :)

Tomorrow I will check the links. And thank you very much!
 

pjug

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#48
I guess I wasn't exactly clear--I was referring to voltage equality at max power output, and along with that, THD+N equality up the voltage ladder between 8 and 4 ohm loads. Obviously any reasonably low output impedance amp will deliver double wattage when speaker impedance drops, until it hits its power limits. See the NAD C 328 and D 3020 for Class D integrated amps, and almost any AVR for A/B amps, which do not double their 8 ohm power into 4 ohm loads.
Got it. Speaking of max power spec, it is unfortunate that amplifier manufacturers are advertising the 4 ohm power spec without making this clear, like Denon is doing https://usa.denon.com/us/product/hifi/amplifiers
 
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amirm

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Thread Starter #49
A question for @amirm : The SNR at 5W is 20dB below the max output SNR, but output should only be ~10dB higher (5-50W). Where is the extra 10dB of SNR at max output coming from?
My power measurements are for clean power. For dynamic range I usually allow the amp to go to max power, clipping and all. This is why I just added the 5 watt measurement. Indeed when testing this amp, I first stopped prior to clipping and got good few dBs lower dynamic range.
 
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#50
Got it. Speaking of max power spec, it is unfortunate that amplifier manufacturers are advertising the 4 ohm power spec without making this clear, like Denon is doing https://usa.denon.com/us/product/hifi/amplifiers
Yes, very confusing, especially for Denon, who sells AVRs that rate power output for 8 ohms (ignoring the absurd headline 800 watt one channel max burst x however many channels BS). I've finally conditioned myself to look at mini amps as 4 ohm rated, but I'm still learning to look at the numbers like I look at AVR headline numbers since so many "50 watt" mini amps are 50 watt at 10% THD (obviously not the case here).
 
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#51
My power measurements are for clean power. For dynamic range I usually allow the amp to go to max power, clipping and all. This is why I just added the 5 watt measurement. Indeed when testing this amp, I first stopped prior to clipping and got good few dBs lower dynamic range.
Gotcha. Makes sense, thanks for the clarification. The 5W number certainly makes it easier to compare across publications as well (e.g. Stereophile at 1W/8 Ohm) when comparing amps (noise floor is my top interest as far as my own future amp shopping)
 
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amirm

amirm

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Thread Starter #52
As promised, here are the headphone measurements.

The PMA-50 has three headphone gain stages that can only be adjusted through the remote control. Unfortunately the remote came with no battery and I don't have a CR2025 button cell to power it. So these measurements are in whatever gain setting it is at right now.

Most important measurement is power so let's start with 300 ohm load:

Denon PMA-50 Digital Amplifier Headphone Power 300 Ohm Audio Measurements.png


Boy, this is very disappointing. I like to see 100 milliwatts or more but we can't even get to 10 milliwatts! Maybe this is how it acts in low gain but why would it clip then? The rise in distortion prior to clipping also indicates an output stage that is stressed so not good regardless.

Switching to 33 ohm load where we usually see more power also disappoints:

Denon PMA-50 Digital Amplifier Headphone Power 33 Ohm Audio Measurements.png


This is not remotely competitive. I could not even get to 1 volt output without it severely clipping.

Here is the output impedance:
Headphone Amplifier Output Impedance Measurements.png


There is nothing remotely good to hang one's hat on. Seems like this is a checklist feature rather than a real attempt at a good headphone amplifier. We have $9 dongles that do better.

It seems like a trend that Japanese companies are behind the times here not realizing the importance of high power and very low output impedance among headphone audiophiles.
 

trl

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#55

restorer-john

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#56
I see that IRF2092 has 800KHz switching freq. too, so I guess it's a legit freq.
Putting the MOSFETs outboard- smart move. IRF have always made some fabulous high powered FETs. I guess you can strap whatever you want on the end in real terms.

The killer however, is the residual noise.

1561973401938.png
 
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#57
You are right about the numbers. SNR-A at 1 watt differ too much. Why? I do not know.
It's interesting. Especially since the distortion and other numbers match other sources quite well in every comparison I've done, as they do here with the PMA 50.
 
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