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Topping NX1s Portable Headphone Amp Review

amirm

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#1
This is a review and detailed measurements of the Topping NX1s portable, battery operated headphone amplifier. It is on kind loan from a member. The topping NX1s costs US US $39.90 from Amazon including Prime shipping! It is hard to imagine that is being sold for so little money.

The NX1s comes in a sturdy aluminum enclosure which belies its price point:
Topping NX1s Portable Headphone Amplifier Phone Audio Review.jpg

The little volume control is a bit hard to rotate given the guard next to it. Given the intended purpose (put in the pocket connected to a phone), it seems like a reasonable compromise.

On the back (not shown) is bass boost and gain buttons. Charging is performed using the USB cable which is convenient. I left it charging overnight and was happy to see the charge light go off so it is not overcharging. I think the specs are 4 hours of charging for 40 hours of playback.

There was no heat generated from the unit.

Headphone Amplifier Audio Measurements
As usual, we start with our dashboard of 1 kHz tone, aspiring for unity gain (2 volts in, 2 volts out):

Topping NX1s Portable Headphone Amplifier Phone Audio Measurements.png


Wow, this is quite good! Distortion is below audible threshold. Noise which is also very low, sets the SINAD (signal relative to noise+distortion). That puts the NX1s in upper class of headphone amplifiers tested:
Best Headphone Amplifier for Phones 2020.png


Signal to noise ratio is quite excellent as well:
Topping NX1s Portable Headphone Amplifier Phone Dynamic Range Audio Measurements.png


But a bit less so with 50 millivolts output, simulating what you get with sensitive headphones/IEMs:
Most Quiet Hiss Free Headphone Amplifier.png


With its competitors all being desktop headphone amps, this is quite an achievement.

The great story so far diminishes fair bit though with frequency response measurement:

Topping NX1s Portable Headphone Amplifier Phone Frequency Response Audio Measurements.png


The output must be capacitor coupled with too small of a cap to cause that low frequency drop. Bass boost compensates for it but goes way too far in the frequency response.

Most important test is amount of power relative to distortion and noise. Here it is at 300 Ohms:

Topping NX1s Portable Headphone Amplifier Phone Power into 300 Ohm Audio Measurements.png


Performance in low gain approaches the limit of my analyzer which is great. Alas, high gain doesn't produce more power and simply clips a bit later. This may be good though given that phones have usually much less output than my simulated desktop DAC (2 volts).

The story is the same with 33 ohm load:

Topping NX1s Portable Headphone Amplifier Phone Power into 33 Ohm Audio Measurements.png


These are higher power ratings (naturally) than any dongle.

Output impedance is a bit high at 4.4 ohm but not too high:
Lowest Impedance Headphone Amplifier.png


Channel imbalance relative to volume control position is typical of analog controls:
Topping NX1s Portable Headphone Amplifier Phone Channel Balance Audio Measurements.png


Headphone Listening Tests
I started my testing with Sennheiser HD-650 high impedance headphones. High gain was useless with the bass heavily distorting at higher volumes. Again, this is with a desktop DAC driving it. With phones, you will likely use the high gain. In low gain, the distortion went away and there was decent dynamic range. Bass as predicted was a bit anemic. Turning on the bass boost fixed that but it screwed up the sound too much for my taste.

Performance with low impedance Hifiman HE-400i was much better with incredibly good resolution and overall performance in low gain.

Conclusions
The distortion and noise measurements of the Topping NX1s are extremely good and go away beyond its budget pricing. The problem is the drop in bass in frequency response. I played with the EQ in Roon player and managed to compensate for that some. But then you have to be careful to not exceed its maximum power capability.

Overall, the NX1s is an unusual product with shining performance in difficult areas (noise and distortion) but not in the easier areas (frequency response). If Topping could fix the frequency response, it would have a winner on its hand. As it is, I can't give it a recommendation. You can decide with the data presented if you want to use it or not.

------------
As always, questions, comments, recommendations, etc. are welcome.

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NTomokawa

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#2
Teardown? I wanna see whether it's capacitor-coupled for real and what the cap values are.
 

Cahudson42

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#6
Just an fyi - you might want to review Amir's earlier NX3s review and compare. It's only $16 more..and has higher 32ohm output which I appreciate with my HE400i. Have had mine a few months after sending back es100 and BTR3 and happy with it.

Don't know if the 3s suffers from the same lf dropoff.. don't remember if Amir had a fr graph in the earlier review..don't remember one..

Topping NX3s Portable HiFi Headphone Amplifiers OPA2140 LME49720 USB Bass Gain Digital Audio Power Amplifier(Silver) https://www.amazon.com/dp/B07JC66T2G/
 

raif71

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#10
So it's somewhere in between the JDS Atom and El Amp II.
Haha...if you go to the Fiio A5 site, the reason I mentioned TCA-HP-1 is that if you look at the SINAD graph there, amir had it in red at the position of TCA-HP-1 but I guess your suggestion that Fiio A5 is between jds atom and el amp II is more like it.
 

bobbooo

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#11
Once again, this just goes to show nothing should be assumed when it comes to measurements in science and engineering, especially an audio product's frequency response - a measurement that has potentially the biggest affect on the audible sound fidelity of audio equipment (be that DACs, amps, headphones, speakers, mics etc.), much more than relatively low levels of distortion.

Frequency response should always be the top priority (over e.g. distortion) on any audio product engineer's or scientific reviewer's list - without consistently covering the basics, other performance metrics are moot.
 
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Johnb

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#12
Just an fyi - you might want to review Amir's earlier NX3s review and compare. It's only $16 more..and has higher 32ohm output which I appreciate with my HE400i. Have had mine a few months after sending back es100 and BTR3 and happy with it.

Don't know if the 3s suffers from the same lf dropoff.. don't remember if Amir had a fr graph in the earlier review..don't remember one..

Topping NX3s Portable HiFi Headphone Amplifiers OPA2140 LME49720 USB Bass Gain Digital Audio Power Amplifier(Silver) https://www.amazon.com/dp/B07JC66T2G/
I also own NX3S and find it quite nice with my HD650's. With a 2V source, don't need to go beyond 3/4 volume. The problem is that unless you couple with a dongle with that output, you are not getting the full benefit. Laptop/phone output is too low. The output impedance is too high for most iem's, the target market for NX1S. I personally don't see the problem with low freq roll-off - very few phones are doing too much there anyway.

The pictures of NX3S internals clearly show output cap, I believe, from memory. Mine cost $45 on massdrop. It is just killer with the 150 ohm hd8x.
 

Johnb

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#13
The build quality on NX3S and I presume NX1s is fantastic, and the larger amp's THD+N on a par with JDS Atom, at least at 300 ohms, and within its power envelope. The JDS atom, which I also own, beats it in control of the low end, but at the volumes I listen to, the difference is not that appreciable. And again, this is a portable amp.
 

Johnb

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#14
The Nx1s misses its target market (iems) because of its output impedance, but 50-150 ohm cans would seem to be its sweet spot. Now that I reread the article, 1db down at 30 hz is a bit much.
 

restorer-john

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#15
@amirm try the FR plot with two load impedances to determine if it is output capacitor related or input capacitor/NFB cap.

Is the output impedance number derived from the AP (swept Freq) one and a worst case number, or a spot frequency test for R-out?
 
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#16
Fiio A5 wins then.
 

restorer-john

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#18
As noted in your teardown and suggested, the input is capacitively coupled. As such, the frequency response will vary with position of the volume control and the source impedance.

I assume you @amirm tested the frequency response with the volume control at maximum (as is standard practice)? Otherwise the plot as it stands is not representative of the actual FR.
 
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amirm

amirm

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Thread Starter #19
I assume you @amirm tested the frequency response with the volume control at maximum (as is standard practice)? Otherwise the plot as it stands is not representative of the actual FR.
It actually is as you would be operating this amp near or at its maximum volume position given its rather low output power. This was the case with headphones I tested.
 
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#20
4.4 ohm a is high enough it could change the sound of many headphones and cause feedback with sensitive IEMS. Since its a mobile device I would say alone would make it a pass for me.
 
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