Potentiality and Actuality
- Functionalities: Filters and impedance measurement.
- Volume control.
- Quality control?
- Its square size is not the most suitable for pairing with a DAP or SmartPhone.
- Slightly warms up during operation.
Link to the Store
According to the information on its website, Xuelin Electronics was established in Shenzhen in 2002. It is one of the first companies dedicated to the research of HIFI player products in China. It was started by Dr. Shi Xuelin (one of the main creators of the Chinese Loongson Project) from the Institute of Computer Science, Chinese Academy of Sciences. Already in 2011, the IHIFI812/960 developed by Xuelin, were DAPS a highly recognised worldwide, with very positive reviews. Xuelin insists on doing things conscientiously, not cheating, not throwing away and developing high quality audio products for audiophiles. It also follows the direction of smooth and warm tuning.
This time, Xuelin has created a new product in its catalogue. It is a USB DAC/Amp, which can be used connected to SmartPhones (Android, iPhone), PCs or compatible DAPS. It stands out for its square design, with a casing made of aluminium alloy and double-sided 2.5d glass. It incorporates a 3000mah lithium battery. It has a 0.91-inch display, Dual DAC Sabre ESS9038Q2M and among other features, its automatic calculation of the impedance of the connected headphones, its gain adjustment based on this calculation, as well as the possibility of choosing between 7 filters.
This review will expand on all these features, as well as the sound and some measurements, as usual.
- Model: XUELIN H7
- Size: 80x80x15mm
- Weight: 150g
- Housing: CNC aluminium alloy sandblasted black sandblasted
- 2.5D double-sided glass faceplate. Main copy software: STM32F030C8T6
- Display: 128×32, 0.91-inch white light OLED display
- USB Codec: DSD Codec SA9227 (9123)
- DAC Chip: Dual ES9038Q2M
- LPF Op-Amp: SoundPlus Precision Sound Release OPA2134
- Headphone Speaker: 310Ma track to track AD8397
- Low Gain Power: 262mW@32 Ohm (3.5mm SE), 1051mW (2.5mm Balanced)
- Medium gain power: 112mW@150 Ohm (3.5mm SE), 448mW (2.5mm Balanced)
- High gain power: 154mW@300 Ohm (3.5mm SE), 598mw (2.5mm Balanced)
- Distortion: (15KLPF 1kHZ Distortion-30dB Volume) 0.0055%.
- Signal to Noise Ratio: 112 dB (1KHZ, 2V-VPP, RL = 1k)
- Filters: 7 different filters
- Frequency response: 20-20kHz + 0-0.035dB
- Battery: 2900MAH 3.7V
- Charging: 5V 2A USB charger recommended
The Xuelin H7 comes in an almost cubic box, wrapped in cellophane, with dimensions 101x101x76mm. It is quite dark and on its front side there is only the brand logo, in gold ink. On the back is a white sticker with the specifications, in Chinese text. After opening the box you can see the H7 inside a protective bag. Underneath, there is a cardboard lid to match the box, which has a hole in its centre. Lifting it reveals the rest of the accessories. The complete contents are as follows:
- The Xuelin H7.
- Two rubber bands.
- One charger with US plug.
- One 1m USB to Type-C cable.
- One 10cm Type-C to Type-C cable.
- Several warranty cards and technical centres.
- User manual, in Chinese.
The packaging is rather plain, but the contents have some interesting things, such as the two rubber bands and, above all, the charger, something that normally never comes with it. Too bad it doesn’t come with an EU plug adapter. On the other hand, the USB cables are coated in nylon and are of quite good quality, although the connections are not gold-plated.
Construction and Design
The Xuelin H7 is an 80mm square pickup, with a thickness of 15mm and a weight of 135g. Its casing is made of aluminium alloy and features 2.5D glass on each side. On the top side is a small 0.91 inch display, with a resolution of 128×32. On the left side face there are 2 buttons: from top to bottom, the power button, the double volume button, which works in rocker mode. On this side, at the bottom, there is also a hole for resetting the device. On the lower side, there are the USB connections, first the charging connection, then the connection to the source device, the 3.5mm SE headphone output and the balanced 2.5mm output.
Internally, the H7 integrates a Dual ESS9038Q2M DAC, the low-power version of Sabre’s high-end DAC, capable of delivering 129db SNR and 120dB THD+N. It mounts the opa2134+ad8397 operational amplifiers. It uses an asynchronous dual clock, operating at frequencies of 45.1584MHz/49.152MHz. The USB interface is Bravo’s SA9227, which has a Windows 10-compatible ASIO driver. Finally, the battery used by the H7 is a 2900mah, 3.7V lithium battery.
The first thing that struck me about this product was that it used a Dual ESS9038Q2M, something that is not very common in this price range. Then, its shape, which is square, something that doesn’t work so well when paired with a smartphone or a DAP. Another great attraction is that it has a small screen, as well as some rather peculiar functions, which I will explain in the section on operability.
To sum up, the build quality is very high, but the fact that it has two large glass surfaces, which could scratch, might not be the best option. The glass used is tough, but I would have chosen to mount it on the main face only. Finally, I think the balanced output would have been more convenient in its 4.4mm format, as the connector is more robust.
The Xuelin H7 is compatible with Android, iOS and PC. By extension, it can connect to notebooks, laptops and tablets. You can buy a version that comes with a lightning to USB Type-C cable. Obviously, as it has its own battery, it does not consume the battery of the connected device. Windows 10 recognises it without drivers, but it has ASIO drivers, which can be downloaded from the web.
The audio connections are the classic 3.5mm Single Ended and the balanced 2.5mm.
The H7 has many automatic procedures, it detects in real time the status of the USB connection and the power input from the charging port. It has a procedure to measure and display the impedance of the connected headphones as well as the bitrate of the processed file. It has a low-power protection circuit, DSD instructions, 7 filters can be configured (FA-M, SL-M, FA-L, SL-L, BRIC, HYBR, APOD) and the selected volume can be displayed. In this sense, the volume steps are 0.5db and range from -127.5dB to 0dB. When switched on, the volume is set to -30dB. The gain mode is automatically adjusted according to the measured impedance of the connected headphones, after performing the impedance detection test. This gain will also be shown on the display. The display switches off automatically after a while, as well as the unit, in case it is not connected to any source or USB charger.
It has several display modes, which are accessed by pressing the menu button:
- Main screen: This shows the status of the USB connection, the volume, the battery and whether it is charging.
- Impedance measurement screen: The measured impedance is displayed, after pressing the volume button. The gain mode is also displayed.
- Sample rate measurement screen: The type of file played and its sample rate is displayed.
- Filter selection screen: The currently selected filter is displayed. By pressing the volume buttons, one or the other filter can be selected.
The battery promises a battery life of 8 hours and needs up to 3 hours for a full charge. In my tests, the battery seems to last less than the specified 8 hours, although it clearly also depends on the usage and the power demanded from the device. But keep in mind that if you leave it plugged in, it also consumes power, even if you are not listening to music. This is something to take into account when using it as a DAC connected to a PC or similar.
The first measure to be discussed is the one provided by the device itself, i.e. the calculation of the impedance of the connected headphones. To do this process reliably, it is best if no music is played during this process. At the SE output it is relatively accurate. For the balanced output, the calculation is not correct. Here is a short list of headphones and their impedance measurement at the SE and BAL output.
Impedance per SE
Impedance per BAL
Tansio Mirai TSMR-2
NF AUDIO NM2+
NS Audio NS5 MKII Extra Bass
As can be seen from the table above, the measurement at the balanced output gives a higher value, ranging between 12.1Ω and 13.5Ω, than at the SE output. Could this difference be the value of the output impedance of the device’s balanced connection? I can’t really say for sure, but from the behaviour of that output with some headphones, it could reveal that this is the case.
On the other hand, the measurements that the balanced output provides, in terms of current, might hint at some kind of limitation. I would like to think that my unit suffers from some anomaly, since the maximum current provided by the balanced output is one third of that provided by the SE output.
No Load SE Low Gain
The SE output, with no load at low gain, is stable over the entire frequency range, up to 1.5V.
15Ω SE Low Gain
At maximum volume, the H7 can provide a stable output of 1.3V, which implies a power of 110mW and a current close to 90mA. At these values, the output impedance is 2.3Ω.
33Ω SE Low Gain
Still at low gain, with this impedance, the H7 provides a stable and clean 1.46V. The calculated power is almost 65mW. The output impedance, calculated with these values, is 1.5Ω.
62Ω SE Mid Gain
At mid-gain, a small amount of roll-off begins to be observed in the low frequencies. At 20Hz, the voltage is 1.82V, while at 100Hz it is 2.03V.
100Ω SE High Gain
The low frequency roll-off effect is much higher at high gain: 2.39V at 20Hz, while at 1kHz the voltage is 3.49V.
300Ω SE High Gain
At 300Ω, the low-frequency roll-off effect persists: 2.39V at 20Hz, while at 1kHz the voltage is 3.6V.
No Load BAL Low Gain
The balanced, unloaded output is a mirage of what it could be: 3V stable over the entire frequency range.
15Ω BAL Low Gain
If a 15Ω resistor is put in and the volume is set to 0dB, the output is as shown in the picture below. You can see clear distortion and unusual current limiting. If the device is capable of nearly 90mA, the proper voltage should be as in the SE output.
However, the maximum output without visible distortion is 0.45V, which implies a current of 30mA, which is a third of what the SE output offers. This is not very normal and I am inclined to think that my unit has a balanced output anomaly.
33Ω BAL Mid Gain
Measurements with this resistor at 0dB are similar. It is necessary to lower the volume again, to find a visibly realistic measurement..
At -8dB, the voltage is 0.871V and the output is clean. Measured current is 23mA.
100Ω BAL High Gain
There is no improvement at 100Ω, 0dB and high gain. In addition, you can see that there is voltage clipping at low frequencies.
In order to see a clean signal, the volume must be turned down to -10.5dB. The low frequency clipping persists, the maximum voltage is 1.86V and the current is 18.6mA, a far cry from the almost 90mA delivered by the Single Ended output.
As can be seen, the frequency response is only flat at low gain. In both the SE and BAL outputs, at mid and high gain, there is a clear roll-off in the low frequencies. In the following frequency response of the SE output it can be seen that the cut is more than 4dB at 20Hz. In my opinion, this effect is inexplicable, as it does not occur at low gain.
When this device hit the market, my interest in it was very high. The legendary brand Xuelin had released a DAC/AMP with a Dual ES9038Q2M, at a very competitive price. And with a lot of nice additional features. When I finally had it at home, I tried it with my best headphones. At first, its sound left me cold, not the analytical sound I was expecting, but rather a warmer and softer sound. Later, I realised that this kind of tuning is the classic tuning of the brand. Still, its quality was not all that I could expect from a premium Sabre Dual DAC. I was expecting a darker background and greater separation, a cleaner, more pristine sound than other ES9038Q2M single ES9038Q2M DACs/AMPS that I own.
In act, its sound is not like that, it is not based on absolute precision, nor is it characterised by enormous resolution. The sound is on the soft side of the equation, with a more diffuse background and an average amplitude. The treble is not analytical, but has the smooth character that marks the Xuelin philosophy. This softness has an impact on the level of transparency, limiting its perception. The tone also has this warm influence. This is how the execution of the upper zone is natural and balanced, without much sparkle, maintaining a state of restraint that does not take risks.
As it is not an analytical sound, the extraction of detail is not as pronounced and is influenced by a somewhat diffuse character and an average clarity, although it is improved by the balanced output. The amount of air remains in the same parameters, being another aspect that influences the sound not to have a great sensation of openness and three-dimensionality. On the other hand, the instrumental recreation becomes remarkable and the warmth of the sound brings a rather harmonious balance and fluidity.
Low end power is evident and the mids are full-bodied. But a more attractive texture is lacking, as well as more authority in the low end. The articulation of the low end is not very remarkable either, and its execution is merely good. In the mid-range, the same level of transparency persists, something that can be felt in the separation of voices and instruments. However, the warmth of the sound brings a body, which goes very well in certain genres.
Looking for differences between SE and balanced output, I started using IEMS with several BA drivers, without any dynamic drivers. At that moment I noticed sound differences between both outputs, using the same IEMS model. After connecting the Tansio Mirai TSMR-2s to the balanced output, in order to analyse the midrange, I realised that their sound was very nuanced, had lost a lot of brightness and detail, becoming very warm. So I set out to measure the frequency response of both outputs. In the graph below you can see the clear cut in high mids and treble that the H7 makes on its balanced output. On the SE output, the H7 behaves normally.
Another example of this behaviour can be observed with the BGVP VG4:
With IEMS with dynamic drivers, this effect is hardly noticeable and there is no impact. Can be seen with the NF Audio NM2+:
As I mentioned earlier, in the section on impedance measurement at the balanced output, it is possible that the balanced output has a relatively high output impedance, which may cause these alterations in the frequency response of the BA IEMS. This is just another conjecture, but it could be a reason for this.
On the other hand, when making my frequency response measurements, I noticed that the samples were not «stable». The above graphs have been heavily smoothed, so that they appear smooth. In the following graph you can see the frequency response of the NF Audio NM2+ taken with the Xuelin H7 and with the E1DA #9038D, which uses the same DAC, but in a simple version.
You can see how the frequency response of the Xuelin is very rough, when the curve is not filtered. I have tried using other USB ports and various IEMS, with the same result. You can see that the frequency response follows the curve drawn by the E1DA, which is completely smooth. I don’t know the reason for this result and if it is a problem intrinsic to the H7 or related to some incompatibility with my installation. I am also unable to determine whether this effect, if it is real, has an impact on the final sound.
Another peculiarity of the H7 is that, in its mid and high gain modes, regardless of the output, there is a roll-off in the low end. Graphically, the drop is clear. But on a real level, as the greatest incidence is in the sub-bass, it is more complicated to feel it. A good bass enthusiast will probably notice that the lower range does not have the punch of other DACs/AMPs. But all this will depend on the headphones themselves, on the musical genre, on our preferences and sensitivities towards that area. Again, none of this happens at low gain. Which makes me think more about the reason for this particularity. In my opinion, I have always thought that a source should provide a flat output, without any roll-off or emphasis in any area. For that we already have the equalizer or the headphones themselves.
In short, the Xuelin H7 is a device with a lot of features: 3 gain modes and two outputs, a total of 6 different states. This gives a lot of play, but not all modes have the same sonic characteristics and my question remains the same, has this been deliberately designed this way?
The Xuelin H7, potentiality, features and performance, is an excellent device. On paper, it is. In action, it is an imperfect product. And this imperfection rubs off on the sound. All the solutions provided should give a result that would place the H7 among the best. But in reality, the sound is good, but no better than other direct rivals. Among its best virtues are the inclusion of the display, its construction and the functionalities, such as filter selection, impedance measurement, volume control, the information provided on bitrate, the three gain modes and the two outputs (SE and BAL). All this should be an eye-catcher for anyone. But when the performance of one or more of these features is not as expected, the goodness of the device remains on paper, in that potential state.
Earphones and Sources Used During Analysis
- HiBy R3 Pro
- Xiaomi Redmi Note 8 Pro
- Hidizs MS2
- Reecho SG-03
- NF AUDIO NM2
- NF AUDIO NM2+
- BGVP ArtMagic VG4
- Tansio Mirai TSMR-2
- ISN H40
- NS Audio NS5 MKII Extra Bass
- Tin HiFi T4
- TFZ Live X
- Rose QT9 MK2
- Ikko OH10
- BQEYZ Summer
- Takstar Pro 80
- NiceHCK EBX21
- Sunrise Dragon 2 Limited Edition (SWD2LE)
For the final assessment of the device, I have left out the problems I have seen with the balanced output: the incorrect impedance measurement, the lower current delivery and the modification of the frequency response of the IEMS with BA drivers. Personally, I think there is a problem with my unit, with that output. That’s why I don’t take it into account. Although I do take into account that the frequency response is not flat in the mid and high gains, as it is common to both outputs.