This is a review and detailed measurements of the MZX Audio PHO-NR1 stereo balanced phono preamplifier. It was sent to me by the company and costs 339.000 Hungarian Forint or about USD $1,017.
I have taken the top off for reasons mentioned below. The front and back panels are plexiglass while top and bottom are fairly thick machined aluminum, giving the unit a rather solid feel. The sole LED communicates something about the settings which I did not bother to learn. What I did have to learn was how to change the gain setting which required getting inside the unit. Documentation is provided on the dip switches but not how to open the unit. I guessed that the four upper screws might let the upper shell and fortunately, I was right:
I really wished the switches were mounted underneath the PCB with a cut out in the case so that you could change them without opening the unit. While the high voltage wires have good sleeves over them, there is still some chance of electrical shock should the owner not unplug the unit.
I had to change the dip switches because the default gain is whopping 72 dB! The input loading is also a very low 1 K Ohm. Even though the unit is advertised as supporting Moving Coil cartridge support, the lowest gain is 52 dB which in my opinion is too high. Since there was nothing lower, that is how I tested the unit.
A nice Meanwell switching power supply is on the left. Unit can be powered with a linear power supply which based on my testing, is completely unnecessary and may make things worse.
My favorite feature is highlighted in the back:
Yes, we have balanced input and outputs which is rare in this category. I like it due to higher immunity it provides for hum and buzz. My testing showed total absence of such which is usually a major chore in testing phono stages.
MZX Audio PHO-NR1 Phono Stage Measurements
Using my standard 5 mv input level showed an output that was 2 volts. This is double of what I typically see and would create an unfair comparison. I lowered that to 2.5 millivolt to compensate for the higher gain:
Output spectrum is very clean, devoid of any distortion products. Channel matching/gain is superb as well. Ranking is way up the chart:
Frequency response showed a response with fair amount of peaking in bass:
I like the high pass filtering but the rise from 30 to 100 Hz could interact with room modes and could cause fair amount of bloat. Or may make a bright speaker more balanced. Somewhat a crapshoot so wished it was not there or so pronounced.
Headroom measurement comparison is difficult since the 52 dB gain is in between what we see in MM (45 dB or so) and MC (60+ dB):
Mentally interpreting, it seems fine to me.
What is way beyond fine and falling in state of the art performance is the extremely low distortion:
While this would be falling on deaf ears of the LP format itself, it is nevertheless nice to see as a show of engineering prowess.
Conclusions
The PRO-NR1 takes the proper approach in producing a balanced input to output phono stage. Very few companies recognize the importance of this architecture and for that, I commend the company. Overall performance ranks from good to excellent with the exception of low frequency response. As noted, having a high pass filter to reduce rumble is good but that peaking should be better controlled.
I can't recommend the MZX Audio PRO-NR1 because of that filter error. Otherwise, the rest of the design is commendable.
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As always, questions, comments, recommendations, etc. are welcome.
Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
I have taken the top off for reasons mentioned below. The front and back panels are plexiglass while top and bottom are fairly thick machined aluminum, giving the unit a rather solid feel. The sole LED communicates something about the settings which I did not bother to learn. What I did have to learn was how to change the gain setting which required getting inside the unit. Documentation is provided on the dip switches but not how to open the unit. I guessed that the four upper screws might let the upper shell and fortunately, I was right:
I really wished the switches were mounted underneath the PCB with a cut out in the case so that you could change them without opening the unit. While the high voltage wires have good sleeves over them, there is still some chance of electrical shock should the owner not unplug the unit.
I had to change the dip switches because the default gain is whopping 72 dB! The input loading is also a very low 1 K Ohm. Even though the unit is advertised as supporting Moving Coil cartridge support, the lowest gain is 52 dB which in my opinion is too high. Since there was nothing lower, that is how I tested the unit.
A nice Meanwell switching power supply is on the left. Unit can be powered with a linear power supply which based on my testing, is completely unnecessary and may make things worse.
My favorite feature is highlighted in the back:
Yes, we have balanced input and outputs which is rare in this category. I like it due to higher immunity it provides for hum and buzz. My testing showed total absence of such which is usually a major chore in testing phono stages.
MZX Audio PHO-NR1 Phono Stage Measurements
Using my standard 5 mv input level showed an output that was 2 volts. This is double of what I typically see and would create an unfair comparison. I lowered that to 2.5 millivolt to compensate for the higher gain:
Output spectrum is very clean, devoid of any distortion products. Channel matching/gain is superb as well. Ranking is way up the chart:
Frequency response showed a response with fair amount of peaking in bass:
I like the high pass filtering but the rise from 30 to 100 Hz could interact with room modes and could cause fair amount of bloat. Or may make a bright speaker more balanced. Somewhat a crapshoot so wished it was not there or so pronounced.
Headroom measurement comparison is difficult since the 52 dB gain is in between what we see in MM (45 dB or so) and MC (60+ dB):
Mentally interpreting, it seems fine to me.
What is way beyond fine and falling in state of the art performance is the extremely low distortion:
While this would be falling on deaf ears of the LP format itself, it is nevertheless nice to see as a show of engineering prowess.
Conclusions
The PRO-NR1 takes the proper approach in producing a balanced input to output phono stage. Very few companies recognize the importance of this architecture and for that, I commend the company. Overall performance ranks from good to excellent with the exception of low frequency response. As noted, having a high pass filter to reduce rumble is good but that peaking should be better controlled.
I can't recommend the MZX Audio PRO-NR1 because of that filter error. Otherwise, the rest of the design is commendable.
------------
As always, questions, comments, recommendations, etc. are welcome.
Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
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