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Review and Measurements of Denon PMA-50 Amplifier

amirm

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#1
This is a review and detailed measurements of the Denon PMA-50 Audio (speaker) amplifier with included DAC and Bluetooth. It is on kind loan from a member. It seems to be discontinued but when available, it cost US $599. I see it on ebay and such from $370 to $450.

The enclosure is more stout and nicer looking/feeling than a lot of products in this category:

Denon PMA-50 Digital Amplifier Audio Review.jpg

The volume control is large and nice feeling. It works a bit odd though in that when you first turn it, it switches the display to volume level but doesn't do anything with respect to changing the level. You need to keep turning it to have it take effect.

There is a headphone amp which I did not test yet. May do that later.

Back panel shows a nice suite of digital and analog inputs but no line out for the DAC:

Denon PMA-50 Digital Amplifier Back Panel Audio Review.jpg

I performed all of my testing with USB and a bit with analog Aux input.

Included mains power supply gets rid of the tangle of wires that comes with external supplies.

Internally this is a "DDFA" design which means it accepts digital input and converts it to PWM for amplification.

Amplifier Audio Measurements
I started my initial test with USB input to the amplifier and got this:
Denon PMA-50 Digital Amplifier Audio Measurements.png


While not state-of-the-art, performance is above average for amplifiers we have tested with respect to distortion:
Best Audio Amplifiers Reviewed 2019.png


Using analog input degrades performance fair bit:

Denon PMA-50 Digital Amplifier Analog Audio Measurements.png


We lose about 5 dB, mostly in elevated noise level. Note the channel mismatch when you use analog input as opposed to digital.

Frequency response using USB input and high sample rate of 192 kHz, shows the noise shaping/filtering of the digital amplifier:

Denon PMA-50 Digital Amplifier Frequency Response Audio Measurements.png


Young people with good hearing may hear some elevated sharpness. Total bandwidth though is better than some other amps we have tested which truncate at 22 kHz and such.

Looking at the spectrum of 1 kHz tone, we see a very well behaved amplifier despite being class-D:
Denon PMA-50 Digital Amplifier 1 kHz FFT Audio Measurements.png


Ultrasonic noise is limited to -60 dB. Some other products have peaks as high as -20 dB here. There is a single spike at 840 kHz or so, which is likely the switching frequency.

Note that I did not have to use my AES filter as I usually do with class D amp. The analyzer was not confused by the ultrasonic noise as present.

Using USB input we get very clean signal until the amp stops producing power:

Denon PMA-50 Digital Amplifier Power at 4 ohm Audio Measurements.png


54 watts of power slightly beats the 50 watt specification into 4 ohm. Alas, this is not much power, relegating the unit to office, small room use.

As expected, power drops with 8 ohm load:
Denon PMA-50 Digital Amplifier Power at 8 ohm Audio Measurements.png


I suggest getting a 4 ohm speaker to extract the max power out of the unit.

Using analog input, we can compare the power at 4 ohm to other amps tested. Here again, the gain was strange as turning it up to 0 dB, caused elevated noise and very early clipping. So I dialed volume down and drove the unit to 2 volt input to get this:

Denon PMA-50 Digital Amplifier Power at 4 ohm Aux In Audio Measurements.png


As we see, its modern competitors all have tons more power.

The digital input though does better as we see in this IMD comparison:
Denon PMA-50 Digital Amplifier IMD Audio Measurements.png


If the PMA-50 had more power, it would be a real contender here.

Signal to noise ratio using USB input at nearly 5 watts and max power yielded this:

Denon PMA-50 Digital Amplifier SNR Audio Measurements.png


We barely miss the spec at max power. Even at 5 watt though, we are reasonably close to noise floor of CD/16-bit audio. So not bad.

Conclusions
The Denon PMA-50 seems to be competently designed. It has none of the performance quirks of cheap class-D amps. It has a solid cabinet and controls to go with that engineering.

The big knock against it is modest amount of power and high price relative to competition. And in this day and age, lack of streaming support.

I personally put huge value on power in amplifiers so can't recommend the PMA-50 on that front. But you have the data and can judge for yourself with your priorities.

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#2
Nice review @amirm!
This frequency response graph freaking me a bit...
Still, this does not look like a bad device for a bedroom-second system, as it could be really cheap (saw at 240€ new).
May you measure the performance of the headphone out?
 
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amirm

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Sure, later tonight I may give it a shot.

On frequency response, note that it goes out to 90 kHz. If I stopped at 20 kHz, it would look a lot better.
 

Xulonn

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#4
Still listed on the Denon USA website as "for sale" for $599 list.

Edit: Oops - my mistake - The PMA-50 has been replaced with the PMA-60 - the back panel has the same connections with a slight rearrangement.

PMA-60 specs:

  • Output power 8 Ohm (20 Hz - 20 kHz, T.H.D. 0.07%) 25W (1kHz)
  • Output power 4 Ohm (1 kHz, T.H.D. 0.7%) 50 W
  • Total Harmonic Distortion 0.004 %
  • Input Sensitivity: High level 70 mV
  • Signal to Noise Ratio: High level 110dB

It appears to be a better and more powerful variant of the Teac AH-01 (~30wpc) ICEpower DAC/Amp that i brought with me to Panama when I moved here in 2012. The Teac lasted 6 years, but was likely damaged when lightining hit the utility pole next to my rental house and took out other electronics - including my UPS/Battery Backup unit.
 
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SEKLEM

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#5
Looks like a robust design. It's nice the PSU is inside the main chassis, especially given the size. This seems like it's geared toward desktop/office/small room given the features and power, and it would appear it would fit that application well. I can live with modest power 98% of the time.
 

SEKLEM

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#6
Still listed on the Denon USA website as "for sale" for $599 list.

It appears to be a better and more powerful variant of the Teac AH-01 (~30wpc) ICEpower DAC/Amp that i brought with me to Panama when I moved here in 2012. The Teac lasted 6 years, but was likely damaged when lightining hit the utility pole next to my rental house and took out other electronics - including my UPS/Battery Backup unit.
The TEAC A-H01 houses the same ICE module that is in the B&K AV30.2 that should be coming up for review in a few (weeks, months?). Unlike the ICE amp, the signal isn't converted to analog before arriving at amplification portion of the Denon. I assume this also means the Denon does an ADC on the analog input.
 

MZKM

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#7
I suggest getting a 4 ohm speaker to extract the max power out of the unit.
Huh?

4ohm requires 2x the wattage [2.83^2 / 8 = 1W ; 2.83^2 / 4 = 2W] and since 54 = 2*27, an 85dB @2.83Vrms sensitive 8ohm speaker and an 85dB @2.83Vrms sensitive 4ohm speaker will get to identical loudness.
 
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#8
I suggest getting a 4 ohm speaker to extract the max power out of the unit.
This is a common misunderstanding.

Speaker drivers a voltage driven devices, so 27W into 8 ohms is the same as 54watts into 4ohms.
V = sqrt(P x R); so in this case V= Sqrt(27x8) = spurt (54x4) = 14.7 volts

So in this case it doesn’t matter whether you use 8 or 4 nominal speakers.

A second note on the low power- what this means in practice is that amplifier will provide about 14dB gain, which is 6 dB less than what a 100Wpc amplifier can muster.

So at maximum, it will sound about half as loud if it doesn’t clip. At clipping it will sound “bad” for experienced listeners.

Interestingly, non trained listeners will hear this as ”too loud” (ie. strained, offensive)

Sincerely,
tk audio science translator 303
 
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GrimSurfer

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#9
Was there any chance of an input impedance or gain mismatch when testing the analog input, Amir? It seems strange for elevated noise and early clipping to occur at normal source levels... unless @SEKLEM is onto something about the ADC on the analog input.
 

amirm

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#10
Huh?

4ohm requires 2x the wattage [2.83^2 / 8 = 1W ; 2.83^2 / 4 = 2W] and since 54 = 2*27, an 85dB @2.83Vrms sensitive 8ohm speaker and an 85dB @2.83Vrms sensitive 4ohm speaker will get to identical loudness.
Don't get me started with speaker sensitivity numbers.... Briefly, you halved the efficiency of the 4 ohm speaker to arrive at equal loudness.
 

amirm

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Was there any chance of an input impedance or gain mismatch when testing the analog input, Amir? It seems strange for elevated noise and early clipping to occur at normal source levels... unless @SEKLEM is onto something about the ADC on the analog input.
The amplifier chip requires a digital stream so the analog input is digitized to create that data. So it makes sense that it has more noise and can have its own overload characteristics.
 

GrimSurfer

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#12
The amplifier chip requires a digital stream so the analog input is digitized to create that data. So it makes sense that it has more noise and can have its own overload characteristics.
Interesting. It might have some technological merit but the approach taken by Denon clearly has an operational limit that could preclude it being used with some devices.
 

MZKM

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#13
Don't get me started with speaker sensitivity numbers.... Briefly, you halved the efficiency of the 4 ohm speaker to arrive at equal loudness.
4ohm speakers are not inherently higher sensitivity, you can have a 85dB 4ohm speaker (e.g., ELAC UB5) and a 95dB 8ohm speaker (e.g., PSA MT-110).

Since this unit doubles down the wattage into 4ohm, it makes no difference whether you get an 8, 6, or 4ohm nominal speaker, they will get to equal loudness if their sensitivities are equal. Thus, when pairing with this amp, look for speakers with above average sensitivity, the impedance is mostly irrelevant.
 
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trl

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#14
Huh?

4ohm requires 2x the wattage [2.83^2 / 8 = 1W ; 2.83^2 / 4 = 2W] and since 54 = 2*27, an 85dB @2.83Vrms sensitive 8ohm speaker and an 85dB @2.83Vrms sensitive 4ohm speaker will get to identical loudness.
Speakers sensitivity is dB/W/1m and not Vrms/W/1m! At exactly the same voltage applied the 4 Ohms speaker will benefit of double amperage, hence double of power, so that means 3dB more per each speaker used.

This is a common misunderstanding.

Speaker drivers a voltage driven devices, so 27W into 8 ohms is the same as 54watts into 4ohms.
V = sqrt(P x R); so in this case V= Sqrt(27x8) = spurt (54x4) = 14.7 volts

So in this case it doesn’t matter whether you use 8 or 4 nominal speakers.[...]
Like I said before, 4 Ohms speakers will draw twice more intensity than 8 Ohms speakers, so doubling the output power will increase the SPL loudness with 3dB/speaker (if amplifier's PSU can handle that). You just proved above that for the same 14.7 Volts on 8 Ohms speakers that means 27 Watts and for 4 Ohms speakers that means 54 Watts, so I don't understand what would be wrong with Amir's assertion "I suggest getting a 4 ohm speaker to extract the max power out of the unit".

P.S.: The only reason why not recommending 4 Ohms speakers might be difficulty with some Class-D amplifiers to handle impedance differences of the speakers (usually 4 Ohms speakers have around 2 Ohms on bass and up to 10-12 Ohms on trebles), but that's a different story.
 
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#16
Speakers sensitivity is dB/W/1m and not Vrms/W/1m!...


... Like I said before, 4 Ohms speakers will draw twice more intensity than 8 Ohms speakers, so doubling the output power will increase the SPL loudness with 3dB/speaker (if amplifier's PSU can handle that). You just proved above that for the same 14.7 Volts on 8 Ohms speakers that means 27 Watts and for 4 Ohms speakers that means 54 Watts, so I don't understand....
The whole dB/W thing VS dB/2.83V thing is part of the source of confusion. Hope this little article from Audioholics and Andrew Jones helps you understand:

https://www.audioholics.com/loudspeaker-design/loudspeaker-sensitivity

Andrew has forgotten more about speakers then I have learnt!
 
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amirm

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#17
Except it does have streaming on-board in the form of Bluetooth. Granted that's not ideal, but it's there... :cool:
Bluetooth is not streaming. And it is lossy so not really the same thing.
 

Juhazi

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#20
54W/4R without clipping is pretty much power actually. For small rooms and destop use that is more than enough for sure. Many people are happy with 5W and 5% distortion...

I use Icepower 50ASX2 modules in my active speakers and for speaker prototyping.
 

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