Topping NX4 DSD

I didn’t intend to do this review at the moment because I have a list of items that I am trying to work through, however, this amp/dac has developed an issue and I need to return it. I must say that Amazon have been very easy to deal with, as usual, to return the product that is a little over 5 months old.

Disclaimers and info

This product was purchased by me, I have not been influenced or even requested to write this review and, as always, I will give my own personal and honest opinion.

Unboxing and overview

I purchased this amplifier in January and at the time didn’t have any intention of creating product reviews, so I did not take photos, all the photos posted are from today as I prepare the unit to be sent back under warranty.

The unit comes packed in a black box with a clear plastic partial cover that shows the name of the product.

Inside the box we find the dac/amp itself along with a user manual, a silicone mat to avoid scratches when stacking with a phone etc., a 3.5mm to 3.5mm short cable, a USB to Micro USB cable, a Micro USB cable to USB type C, a Micro USB to Micro USB cable, various velcro stickers and 2x rubber rings for stacking with a phone or DAP etc.

The unit itself is quite small and thin, having dimensions of 11 x 6.8 x 1.4cm, this means it can easily fit in a pocket. The DAC/Amp is completely made of metal and, while it is light, it does feel like a decent quality item.

On the back of the unit there are two Micro USB ports, one labelled “Charge” and the other “DAC”. As you can probably guess, the “Charge” port is for charging the internal battery of the device, while the “DAC” port is for data connectivity. At the side of each port there is also a small LED. The LED located by the “Charge” port turns red when the unit is charging and then green once charging is complete. The other LED, located at the side of the “DAC” port, turns blue when there is a signal and red when DSD is being received by the unit.

Depending on your use, this is either a positive or negative point. Personally I like the two port set up as it means that the NX4 DSD is not constantly charging while in use, however, it does mean that you will need an extra cable if you want to charge the unit while in use.

On the front of the unit there is a volume knob which is slightly recessed into the unit. This knob also functions as an on/off switch, clicking mechanically into place when it is turned to zero (off). The volume knob has a nice feel and operates very smoothly, however, the fact that it is recessed into the body and is flush with the width of the unit means that it is very difficult to operate if laid on a desk or similar.

On the front we also find two 3.5mm ports. The first is for the headphone output, located on the left as we look at the front, the other is the line in/out port. The line in/out port can be used either as an input or an output depending on what is connected. The function is automatically determined by the unit.

Between the ports and the volume wheel, there are two micro switches. One of the switches (left) allows selection between high and low gain, while the second switch is to activate the bass boost.
The last thing we find on the front is another small LED, located above the micro switches, labelled “Power”. This LED turns blue when the unit is on and turns to red when the internal battery is low, reminding you to charge the unit.

Functionality

The NX4 DSD is a very simple unit to operate. It is as simple as connecting the cable from whatever source you are using, via USB, to the DAC port on the rear or, if you are sending analog audio and only using it as an amplifier, then connecting to the “Line In/Out” port on the front.
I have mainly used this unit as a DAC/Amp, connecting via USB from whatever source I choose to the Micro USB port on the back. For the last 5 months I have used this unit mainly connected to a Xiaomi Note 4, a Shanling M0 and various Windows 7 & 10 computers. The unit has functioned with ease connected to all of these devices, although I did have a few quirks when connecting to one of my laptops (Windows 10) as it kept reinstalling the device. I finally erased all drivers and installed those from the Topping site which have not given me any issues since.

When the unit is receiving data via USB, the line in/out port is automatically a line out. The line out is a fixed line out (no volume control) and you may also use the ‘phones out port at the same time (this is obviously controlled by the volume wheel).
I have had no issues with the unit playing back any number of formats I have sent to it, including Spotify, MP3, FLAC and DSD.

If the NX4 DSD is not receiving data via the micro USB port, then the line in/out port automatically becomes line in. This allows the use of a different DAC if preferred, using only the amplifier section of the NX4 DSD.

The issue for which I am sending this unit back under warranty probably should fall under “Functionality” as it is relative to the DAC Micro USB port. Over the last month or so, the port has developed a “looseness” which means that if the unit is moved then connectivity is lost with the source. This is not only irritating because the connection fails, but it also means that whatever source is playing usually either pauses or stops (depending on the device) and in the case of the M0, it means that the track will start again from the beginning if you press play. I did actually contemplate using cable ties to hold the micro USB cable in place, which works quite well, as I didn’t want to return the unit, but in the end I have decided that I would rather not have to deal with this on a relatively new item.

Sound

There is a complete set of measurements over on ASR that gives specific details for those of you that seek them, however, I will give my own impressions on sound along with a couple of FR graphs I made myself in REW.

I find the unit to be pretty flat and neutral, which is personally what I look for in an amplifier, but looking at the graphs that I made (and those posted on ASR) it does show a roll off starting around 15kHz. It also shows a very slight roll off in the lowest frequencies. However, my latest hearing test reported that I could hear ok up to just over 18kHz and I can’t say that I have felt any kind of information lacking in the highest registers. Personally, I find the sound to be uncoloured and pretty close to the sound coming from my JDS Labs Atom although the Atom does provide a clearer definition and much more power.

I have measured frequency response between channels and also comparing 100% on the volume wheel against 50% of the volume wheel and there is absolutely no difference in frequency response. Please note that I calibrated the measurements so that the were both shown at the same part of the graph, therefore, do not take any notice of the dB levels in the following graphs.

Here is a graph that shows Left at 100% volume, Right at 100% volume, Left at 50% volume and Right at 50% volume, all overlaid. As you can see, there is no difference in frequencies or channel imbalance at these levels.

However, when using the NX4 at volume levels below 10%, there is a clear channel imbalance that makes the unit unusable at these levels. I’m afraid I don’t have the equipment necessary to measure the difference at such low volume levels so I am not able to show a graph of this issue.

You can also spot in the graphs the roll off in frequencies that I mentioned above.

When comparing the low gain vs the high gain, again there are no differences at all in response:

When we get to comparing the Line Out vs the Phone out, it this case there is a slight difference in the lowest frequencies, it seems that the Line Out does not have the minor roll off that the Phones Out has. This is not a difference that I can claim to hear, as the difference is minimal, and the fact that a different amplifier is being used will have far more effect on the sound than this minimal change in FR.

One interesting thing about the NX4 DSD is the Bass Boost functionality. When activated it adds a very noticeable boost in the low frequencies, however, it manages to do this in a very smooth way without feeling overpowering or causing any negative impact on the other frequencies. Having said that, looking at the graph below, whilst it boosts the frequencies up until approximately 300Hz, it also reduced the frequencies above 300Hz, which could help explain how it manages to give a good bass boost without causing any kind of distortion.

Power

I have run all of my headphones and IEMs using the NX4 DSD (not all at once!) and I have not found it to be lacking in power with any of them, even the HD6XX can be driven to levels that are above my usual listening volumes. Obviously each person listens at different volumes and I am not someone who loves to blast music as I have grown to respect my hearing, so your mileage may vary. It does not have as much power as a desktop solution such as the JDS Labs Atom, this would not replace the Atom on my main set up, but it does offer plenty of power on the go and also would be more than adequate for someone looking for a nice portable solution.

Conclusion

I have been using the Topping NX4 DSD daily for the last 5 months and I must say that I would continue to do so if it wasn’t for the connector failure that I mentioned above. It has been my main amp when travelling and I have used this (along with the Atom) to do my general listening tests on all of the IEMs that I own up until this point, I am very sad to see it go back.

Will I replace it with another one?.. I am not sure.

Not because I don’t like the product, as I feel it is a great option for its cost, it is more due to the fact that I am not a huge lover of stacking things while moving around so I think that the refund will probably go towards funding a DAP that offers an all in one solution as Source, DAC and Amp.

Would I recommend this?.. Yes, I would recommend this to anyone who is looking for a decent portable solution at a price that is very reasonable.

(This review is also published in Spanish on my blog: achoreviews.blogspot.com)

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