Today on review is the first external USB DAC 
digital-to-analog converter for smartphones and laptops Astell&Kern USB-C Dual DAC Cable PEE51 from the Korean company Astell&Kern , which specializes in top-end audio players, and also periodically collaborates with well-known headphone manufacturers.
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At the very end of 2021, we already had a review of the Astell&Kern SP2000T player from the top A&ultima line. Now the turn of a more mundane, but no less interesting device has come; so we will understand from the point of view of a simple user who wants to get a qualitatively different sound from his smartphone.
DAC is a digital-to-analog converter, a device for converting a digital code into an analog signal. It is used in various devices, but in the context of an overview for audio playback. Thanks to this component, a digital recording from the media is converted into an analog signal, which is reproduced by headphones, speakers and any other audio equipment.
Packaging and equipment
DAC The Astell&Kern digital-to-analogue converter is packaged as ascetically as possible, but at the same time in the sustained style of the brand. A small black box hides only the device itself, which lies in a dense protective material, and documentation.
I would like to see at least an adapter from USB-C to USB-A in the kit, but this is the position of the brand: a minimum of accessories for your money. A&K doesn’t even bother to include a case with their players cheaper than $2000, so you don’t have to get used to it.
Design and ergonomics
The device fully complies with the brand’s design code – it is a rectangular metal bar, which is decorated only with broken edges on the top side, a white LED and logos.
In terms of convenience, everything is not as simple as with Astell & Kern players, which are contraindicated to wear without a case if your pockets are dear to you. Despite the sharp edges, using Astell&Kern USB-C Dual DAC Cable PEE51 (with the naming everything is so-so this time, yes) is still comfortable, it does not cut into clothes and is not felt even in the pocket of tight-fitting jeans. The DAC is not at all bulky and takes up almost no space; with a weight of 25 grams, you don’t feel at all that the smartphone has become heavier.
A 4-core cable made of oxygen-free copper with the addition of silver is responsible for signal transmission; it is covered with a reinforced braid that protects against fracture. The cable is flexible and feels very secure. Judging by how many layers it is made of, it gives the impression of armor-piercing, but how it will be in practice, you need to look after longer use.
The USB-C connector is very secure and does not fall out even from the very loose entrance of my Google Pixel 2. When used with a laptop input, you generally have to put so much effort to remove it that it is almost impossible to do it with one hand without risking damage to the devices.
Specifications and materials
General
- Model: AK USB-C DUAL DAC AMPLIFIER CABLE (PEE51)
- Body material: zinc alloy
- DAC: Cirrus Logic CS43198 x 2
- Sampling frequency: PCM up to 32bit/384kHz, DSD64(1bit 2.8MHz), DSD128(1bit 5.6MHz), DSD256(1bit 11.2MHz)
- Input: USB Type-C Input (Windows 10, Android Smartphone & Tablet PC, macOS)
- Output: 3.5mm
- Dimensions: USB Plug: 17mm x 50mm x 10.3mm / 3.5mm Headphone: 12mm x 20mm x 8.2mm
- Weight: ≈25 grams
Detailed characteristics of the audio path
- Frequency response: ± 0.030 (20 Hz~20 kHz)
- Signal-to-noise ratio: 118dB @ 1kHz, Unbalanced
- THD+N: 0.0004% @ 1kHz Unbalanced
- IMD SMPTE: 0.0003% 800Hz 10kHz(4:1) Unbalanced
- Output impedance: 2 ohm
- Output power: 2 Vrms
Technology
The DAC supports all available music formats up to 32bit 385kHz and also provides native support for DSD256. Two Cirrus Logic CS43198 are responsible for sound processing, which are installed in the younger player of the Astell&Kern A&norma SR25 brand, but more on that below in the sound section.
PEE51 does not have native MQA support; however, MQA is a very controversial format, so its absence is not so critical for most music lovers. Also, the DAC does not work through Lightning, which is a clear minus, but this is quite understandable by the low bandwidth of the connector. Perhaps, over time, they will also release a version of the device on a proprietary Apple connector. With a MacBook Air via USB-C, it works without problems.
The device supports ROON compatibility, which will be a plus for users of this service, although it is not very popular in Ukraine.
Use cases
Why do you need such a device at all, when you can safely buy a cheap USB-C to 3.5 mm adapter and enjoy life? This question is easiest to answer with a direct comparison, but we will try to understand the text format.
First of all, when switching from a conventional USB-C-3.5mm, the detail, volume, panning of instruments and the overall information content of the headphones immediately increase, which can be easily noticed even by the “naked ear”.
Personally, the author prefers to use an audio player, but the convenience of external DACs cannot be denied – you just connect it to your smartphone and go about your business. It doesn’t take up any space at all compared to a standalone player, but takes the sound to a completely different level. This is especially noticeable on tighter headphones, which the smartphone’s built-in amplifier simply cannot pull out; for example, such as Meze Liric , the review of which has already been released earlier.
Although the headphones are not too heavy, they are still full-sized isodynamic emitters, so you can’t call them malleable, and it’s not very advisable to use such a technique with a smartphone. On in-ear models, there is also an increase, but how significant it will be depends on the complexity of the headphones and the nature of their presentation.
When I used the Astell&Kern USB-C Dual DAC Cable PEE51 for the first time, I didn’t immediately understand why it sounded so familiar, because I hadn’t had a chance to get acquainted with the specifications of the device yet. And, as it turned out, the same DACs are installed on board as in my Astell&Kern SR25 player (the price tag of which is around UAH 21,000).
From the point of view of the buyer, this is a solid profit, because in fact you get the sound of a very good player in its purest form, without paying for another extra device with its own display, battery and large case. So if we consider such a device as a replacement for a full-fledged audio player, or as an opportunity for a tangible sound upgrade, this is a very workable option.
Sound
Let’s consider how Astell&Kern USB-C Dual DAC Cable sounds on the example of several models from different “weight categories”. We will compare, again, with the sound from a simple USB-C to 3.5 mm adapter, as well as with the A&K SR25 player.
Meze Lyric
Meze Liric comes first in terms of buildup severity, and already here A&K PEE51 gives odds to most simple players, not to mention a simple adapter. Trite adapter can not even provide the proper volume level. Panning and detail suffered the most when using the adapter, so here Astell & Kern USB-C Dual DAC Cable wins dry in all respects.
Campfire Audio Solaris SE and Ambient Acoustics MAD6
Of the high-end in-channel models, the DAC was tested with Ambient Acoustics MAD6 (6 armature radiators) and Campfire Audio Solaris SE (hybrids of 1 dynamic and 3 armature). On this category of headphones, the increase in the detail of the upper and middle frequencies, as well as the increased accuracy of the panorama, is most clearly audible.
This is easily explained by the demands of multidriver systems not so much on the amplifying path, but on the control of the emitters; a simple adapter does not cope with this task at all. The difference with the A&K SR25 player is not noticeable at all on this type of headphones, so it’s almost impossible to blindly determine which source (player or DAC) is currently connected to the in-channels.
Campfire Audio Honeydew and Shure SE215
Campfire Audio Honeydew and Shure SE215 served as in-ear models from the middle segment for the test. Different in their presentation, but rather bassy, the models worked together with the device no worse than the older Campfire Audio Solaris. On such headphones, there is still a noticeable increase in the amount of information, especially in terms of working out low frequencies, but not as striking as on multi-driver models.
Bottom line, I can say that I prefer not to use a DAC for a smartphone because of the low information content and slightly distorted sound, compared to what a high-end audio player can produce.
But this device made me wonder if I even need a player, if the DAC for almost 5 times less price is almost in no way inferior in sound. Models from other manufacturers have always been a compromise for me and rather acted as a temporary replacement, but the Astell&Kern USB-C Dual DAC Cable can be safely used as the main sound source (or as a traveling option if you cannot give up your favorite audio player).
Cost and competitors
The retail price of new items in official stores is 4620 UAH. A rather big price for an adapter for connecting headphones to a smartphone, but quite justified as for an almost ideal, in my opinion, compact external DAC that can replace a player from the initial models of the top segment.
The closest in sound and detail level to the Audioquest Dragonfly DAC Red for 6119 UAH. It will be slightly superior to the review device in terms of presentation and “musicality”, but it must be connected through adapters. This unties the hands in terms of variability of use, but in terms of moving around the city, such a setup is as inconvenient as possible. So the bundle is viable, first of all, for stationary use.
Also, in the region of 4 thousand UAH, you can look towards good Bluetooth adapters, such as FiiO BTR5 . A great device if you are not ready to give up your favorite wired headphones, but want a wireless connection. Quite powerful, so it can swing not too tight full sizes, but still Bluetooth does not live up to the wire in quality.
Well, more budget options in the face of DD HiFi TC35 Pro Eye Type-C for 2800 UAH and the popular iBasso DC05 for 2100 UAH. Not bad devices that will definitely be better than simple USB-C to 3.5 mm adapters, but in my subjective opinion they color the sound too much. The detail and amplifying path of such DACs are significantly inferior to full-fledged audio players, but as an option to increase the sound level from a smartphone, it is quite viable.
