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Review and Measurements of Topping NX4 DSD Dac and Portable Headphone Amplifier

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But, assuming for a moment that your source is not current-limited, 50 mW into a 93 dB/mW headphone would yield about 110 dB.
Is that not enough volume?
Well yes 110 dB is okay. I do like loud though. When I hand my headphones to anyone else they always turn them down because they say it is almost enough to hurt their ears. Where for me the volume is just getting good. And if my Mac is 45mW (I mistakenly remembered 50 before) with 1.2V that makes the current 37mA. All of those numbers are just a hair below the “Fairly loud” figures on the digizoid calculator. And that is exactly what I expected from experience before looking at a single number. When I set the volume to 90% it is what I would call “fairly loud” (but not quite loud enough), but when I kick it to 100% volume it begins to distort a little. But that leaves ZERO room for EQing. I would have the draw the preamp down to make it much quieter to allow for a +3dB increase anywhere, if I want to avoid distortion/clipping. The signature is pleasant at that point once I draw down -6dB out of the problem 500K, but then the headphones are too quite.

The simple fact is that I have the wrong headphones, but rather than chase 30 different headphones, I figure I will stick with the girl I brought to the dance rather than searching the room for a new one. She’s just Janie Briggs with the glasses, ponytail and paint covered overalls (Not Another Teen Movie reference). A bit of EQing and the signature is just as happy to my ears as my D40x’s (with way better clarity).

By my calculations *pushes glasses up bridge of nose* I will get to get away with around a +3dB increase or a bit more from the NX4 versus my Mac. This is assuming the doubling power requirement of a +3dB increase is purely current. The Mac caps around 37mA where the NX4 at around the same voltage is 66mA. Maybe I’m wrong (you guys know infinitely more than me about this stuff) but that should allow +3dB safely.

On the other hand, the Atom which is also coming in the same day will allow around 1A of current which will be more than enough to EQ that headphone to death if I wanted to. Though +3dB should be fine, I might want a bit more and the NX4 likely won’t allow that. So we will see on Tuesday.
 

dc655321

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Yeah, I gathered that ;)
Just a suggestion, but learn to appreciate lower volumes and take care of your ears.

The simple fact is that I have the wrong headphones
It sounds like that may be the case.
Another suggestion for EQ'ing is to reduce power at some frequencies rather than boost at others. YMMV.

the Atom which is also coming in the same day will allow around 1A of current
Not sure how you arrive at 1A figure. Did you mean 1W @ 33Ohms?
At any rate, yes, the Atom should have enough power for almost any headphone.
Good luck.
 

MrC

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Just a suggestion, but learn to appreciate lower volumes and take care of your ears.
^This!!

As someone who has been on loud to very loud stages for over 20 years, I have lost count of the music lovers around me that can no longer enjoy that love due to excessive volumes.
 
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It seems I all of the sudden rich in caring mothers :) No I'm kidding, its much more like grandmothers. I hope you guys are willing to back that up and wipe my bottom too ;)

Joking aside though, it’s an entirely subjective guess that I listen to an unsafe level. Different people define loud differently but there is an objective decibel of danger somewhere north of 80dB. And I don’t listen to “lawn equipment” level (90+dB) and way below club “can’t hear your friend right beside you” level (120+dB). So I think I may have misstated my loudness before rather saying that I think it is entirely possible the people that think I listen loud are maybe just babies. I definitely am in pain at a concert and even a lawnmower irritates my ears, I never am irritated even after hours of music.

Another suggestion for EQ'ing is to reduce power at some frequencies rather than boost at others. YMMV.
Yes I learned this recently, never having realized it before. That is the -6dB out of 500K that I was speaking about before. I tried JUST taking down 500K to -9dB and not raising highs or lows at all, but it didn’t sound as good as -6dB and +3dB though it maybe be a limitation of my software EQ. The Loki may offer a TRUE -9dB. That will be interesting to test the difference between software and hardware.

Not sure how you arrive at 1A figure. Did you mean 1W @ 33Ohms?
At any rate, yes, the Atom should have enough power for almost any headphone.
Good luck.
I am figuring this off of 1W at 1V (meaning 1A) At least that is what I read Amir’s graph to be saying (roughly 1V). I could be reading it wrong though.
 
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Sorry I should have added that I was focusing on the amps/current because it is not a high impedance but a low sensitivity headphone where the current is the issue. Going by the Digizoid calculator at “fairly loud” needing 37mA, that would mean that a +12dB (not that I would ever do that) would change that to nearly 600mA. I am assuming there that the doubling power effect for every +3dB is only increase the current requirement because I didn’t expect it would increase the need of voltage. That’s a total guess though.

So if something was “1W available” because it was 4V, that would make that 250A to make 1W, which is less than half of the 600mA needed for 12dB. Again I am not saying I would do that but it nice to know it would be there at least from what the Atom could do. It was to avoid saying “it’s got a full Watt” and someone saying “but it’s the current that matters”. So I just went ahead and said 1A.

A philosopher once said that the best jokes are the ones that need explanation (that didn’t happen) and even better is an explanation that needs an explanation :)
 
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Oh and I realized that I was misjudging the “fairly loud” on digizoid, just assuming that “moderate” had to be less than what I listen to. This seemed backed up by the timing of the distortion between my headphones with the Mac. Definitely the Mac can handle 12mA and 5W which is their “moderate”, but that assumption was before I was calculating in the EQing. But realizing that their “moderate” is 100dB (wow that’s louder than a typical lawnmower how is that “moderate”), I now see that moderate or lower is what I need to expecting is needed. That’s a max of 48mA (for +6db — unlikely) or MAYBE 96mA (if butchering the original sound is just what sounds best — but even less likely).
 
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Ha! I just realized I kept saying “500K” instead of “500Hz”. It’s my first time writing in English or using abbreviations, so... mistakes are somewhat reasonable. I hope I didn’t let anyone down. I know a lot of people had a lot of money riding on me getting this right. To those people and to my wife and children, I’m sorry.

#sarcasmjuice
 
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dc655321

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I am figuring this off of 1W at 1V (meaning 1A) At least that is what I read Amir’s graph to be saying (roughly 1V). I could be reading it wrong though.
I think you're mixing up units and what they mean. No biggie.

Are you referring to the graph of the Atom's THD+N as a function of output power?
That is for a 33Ohm load (close to your HE-4xx), and sqrt(1.1W * 33Ohm) = 6Vrms, or sqrt(1.1W/33Ohm) = 0.182A of current.
For the HE-4xx's sensitivity of 93 dB/mW, that power would produce a loudness of 93 dB + 10*log(1100mW/1mW) = 123 dB.
Ouch :)

I am assuming there that the doubling power effect for every +3dB is only increase the current requirement because I didn’t expect it would increase the need of voltage. That’s a total guess though.
Amps are voltage devices - their output is a voltage signal varying with time.
The current they produce is determined by the load (headphone) impedance, up to the maximum current that the device is able to source/sink.
 

dc655321

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How does the NX4 measure up against the Mojo purely on line-level DAC performance?
Welcome to the forum.
The NX4's line-level performance was not measured here, only its headphone out.
But that measured similarly to the Mojo (in fact, slightly better in some respects).
I would expect the NX4's lineout function to perform as well, but without measurements we can't be certain of that.
 

MrC

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Although this is not an issue withe NX4 DSD, I thought I would share an experience I have had in case someone has a similar issue.

I use magnetic stands for a lot of my devices (phones, tablets etc.) on my desk, in the car, kitchen etc. These are the kind that I am referring to:



As I have been using the NX4 DSD on my desk at work, I added a metal sticker (like the one in the photo above) to the back of it and stood it on one of these to make using the volume control easier.

I started experiencing issues where Windows (both Win10 and Win7) would recognize the NX4 and show it as outputting sound (the DAC also had the signal light lit up on the back) but the Topping would not output sound.

I uninstalled/reinstalled drivers, changed ports, all kinds of the usual fault finding up to the point where the device was now showing up as "Topping NX4 DSD (14)", in the typical Windows fashion of keeping to increment numbers on each install. I would get it to work and then after a reboot it would be back to the same issue. I was also experiencing this on my Android tablets but never on my Android phones.

Anyway, the point is that after plenty of scratching my head, I realized that the only variable was that when connecting it to my phones, the NX4 wasn't on the magnetic stand as the micro-usb to micro-usb cable I had at hand was to short to do this.

It turns out that if the Topping NX4 DSD is on the magnetic stand when Windows (or Android) is booted, the device shows as connected and outputting sound, but no audio is actually output (nor via headphone out, nor line out).

If the unit is not on the stand when the OS is booted, then it works fine and putting it on the magnetic stand (once booted) does not cause it to stop working (or any issues that I can notice). You can also turn off the unit and disconnect the cable without removing it from the stand and it will reconnect fine and work fine, the only time this happens is if booting the OS or switching UBS ports while it is on the stand.

I know this is a weird issue that will probably not be an issue for anyone but I thought it worth sharing.
 
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Hi, a proud owner of this wonderful DAC/AMP combo. Very powerful output, can drive my Sony Z7 at ease with high gain @ 50% vol, and also those power hungry planar. I notice no one posted internal pics of this beast (unless i missed it). So here it is (anyone want components name or hi-res pic, you can PM me). My unit has a flat head screws, I actually had a earlier unit with pentalob? screw, a bitch to open it.
FB_IMG_1550428630909.jpg
FB_IMG_1550428636494.jpg
I also replaced stock WIMA caps on my own NX4DSD with something more classic to suit my taste, Nichicon UES caps. Made this beast even better. On iFi counterparts there are only those small SMD caps so I cant tinkering with, a minus for iFi and big plus for Topping :D Anyone with brave steady hands can even replace those tiny Opamp with something else or modded a socket into it for big and easy opamp rolling (SOIC-8 to PDIP-8 socket)
 
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Although this is not an issue withe NX4 DSD, I thought I would share an experience I have had in case someone has a similar issue.

I use magnetic stands for a lot of my devices (phones, tablets etc.) on my desk, in the car, kitchen etc. These are the kind that I am referring to:



As I have been using the NX4 DSD on my desk at work, I added a metal sticker (like the one in the photo above) to the back of it and stood it on one of these to make using the volume control easier.

I started experiencing issues where Windows (both Win10 and Win7) would recognize the NX4 and show it as outputting sound (the DAC also had the signal light lit up on the back) but the Topping would not output sound.

I uninstalled/reinstalled drivers, changed ports, all kinds of the usual fault finding up to the point where the device was now showing up as "Topping NX4 DSD (14)", in the typical Windows fashion of keeping to increment numbers on each install. I would get it to work and then after a reboot it would be back to the same issue. I was also experiencing this on my Android tablets but never on my Android phones.

Anyway, the point is that after plenty of scratching my head, I realized that the only variable was that when connecting it to my phones, the NX4 wasn't on the magnetic stand as the micro-usb to micro-usb cable I had at hand was to short to do this.

It turns out that if the Topping NX4 DSD is on the magnetic stand when Windows (or Android) is booted, the device shows as connected and outputting sound, but no audio is actually output (nor via headphone out, nor line out).

If the unit is not on the stand when the OS is booted, then it works fine and putting it on the magnetic stand (once booted) does not cause it to stop working (or any issues that I can notice). You can also turn off the unit and disconnect the cable without removing it from the stand and it will reconnect fine and work fine, the only time this happens is if booting the OS or switching UBS ports while it is on the stand.

I know this is a weird issue that will probably not be an issue for anyone but I thought it worth sharing.
There are 2 small relays (Omron-made) inside the unit, so it will be affected by the magnet
 
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Hi, a proud owner of this wonderful DAC/AMP combo. Very powerful output, can drive my Sony Z7 at ease with high gain @ 50% vol, and also those power hungry planar. I notice no one posted internal pics of this beast (unless i missed it). So here it is (anyone want components name or hi-res pic, you can PM me). My unit has a flat head screws, I actually had a earlier unit with pentalob? screw, a bitch to open it.
View attachment 22107
View attachment 22108
I also replaced stock WIMA caps on my own NX4DSD with something more classic to suit my taste, Nichicon UES caps. Made this beast even better. On iFi counterparts there are only those small SMD caps so I cant tinkering with, a minus for iFi and big plus for Topping :D Anyone with brave steady hands can even replace those tiny Opamp with something else or modded a socket into it for big and easy opamp rolling (SOIC-8 to PDIP-8 socket)
Where is the ESS chip? I don’t see it in your pics.
 
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Anyone know what ESS reconstruction filter is used? (e.g., Minimum Phase Fast [default on many recent ESS-based DACS] or maybe Linear Phase Fast?). Did anyone see an impulse response test that we could infer the filter from?
 
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Anybody having problem with their NX4DSD regarding the issue with PCM 768k? I discovered on both of my unit (early silver, probably rev 1 with pentalobe screw and rev 2 black with flat head screw, wrongly dismissed as my fault on 1st unit due to i dropped it before, when i got 2nd one then its not my fault :p ) that when you use the upscaling feature on your music player (I used Neutron Pro on my Android and HQPlayer on PC, pm me for exact settings), crank it up to the max PCM 768k (advertised by Topping as supported) after some playback time the NX4DSD would fail to produce sound and only output static/white noise. A reboot (turn off and on) would restore it back to normal. Also the sound is very noisy when input with 768k, dialed it back to 384k and lower then clean sound again. I think there is a bug on the XMOS chip, IDK.
 
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Anyone know what ESS reconstruction filter is used? (e.g., Minimum Phase Fast [default on many recent ESS-based DACS] or maybe Linear Phase Fast?). Did anyone see an impulse response test that we could infer the filter from?
Me too would like to know that!
 

dc655321

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Anyone know what ESS reconstruction filter is used? (e.g., Minimum Phase Fast [default on many recent ESS-based DACS] or maybe Linear Phase Fast?). Did anyone see an impulse response test that we could infer the filter from?
Create an impulse train, 100Hz @ -3dB and save it to a FLAC file:

Python:
import numpy as np
import soundfile as sf

data = np.zeros(44100)
data[::441] = np.sqrt(2)/2

track = np.tile(data, 500)
stereo = np.column_stack((track, track))
sf.write('100hz_3dB_impulse.flac', stereo, 44100, subtype='PCM_16')
Play the generated file through the NX4 in DAC-only mode and look at one of the output channels on an oscilloscope.
Looks linear-phase to me...

nx4_impulse_500us.png
 
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