Astell&Kern AK70 Portable High-Resolution Audio Player


New Head-Fier
Pros: Expansive sound stage, sublime detail and separation, Use as a dac / external sound card, great looks and really easy to use UI.
Cons: Expensive, Wireless lacks range, mint green colour is a bit horrible but the black edition is nice.
I used to play drums in a studio with a few bands back in the day so I guess I have a bit of an ear for what sounds good, well for me at least!
I bought the AK70 as I travel a lot and my phone sounds crap and drains the battery when I listen to music. I read a few reviews prior to auditioning at Harrow Audio in North London. To be honest I can't believe just how good the unit sounds even through my IE80's, I need to get better IEM's! The first thing that you notice is the huge sound stage both deep and wide and just the shear timbre of sound. The separation of instruments is really lovely especially with binaural recordings.
The only criticism is the wireless or rather lack of it. I use Tidal and you need to be near the router for the AK70 to get the wireless signal, this is a minor point really as I mainly listen to it away from home, playing hi-res files. £499 is quite expensive too, so God only knows what the really high-end Astell & Kern sounds like because the AK70 sounds amazing. This is the most I would pay and I am not disappointed at all.
Thanks for the review. Is there a bluetooth option in the ak70? (For wireless headphones) If so, how is the sound?
I haven't used the bluetooth and to be honest I probably never will. Sorry it's not a feature of the AK70 nor infact audio playback that I would consider using. Cheers.


Headphoneus Supremus
Pros: Premium build quality, small size, balanced output, USB DAC & USB Host function, 200GB exFAT mSD compatible.
Cons: No protective case included.
Big thanks to SKM Technologies Singapore for the loan of the AK70 demo unit, and also to Zeppelin & Co. for their hospitality and for providing such a great place to test audio gears and meet nice people!


Being small and more affordable than most of Astell&Kern Digital Audio Players (DAP), AK70 is positioned among AK entry level DAP right after AK Junior. But don't underestimate the small series number and the small size, as AK70 sonic performance is actually competing quite well with its bigger brother, the AK300. We will see that later in comparisons with other DAPs. AK70 is also the first AK DAP to support USB host feature, for connection to other external USB DAC.

Zeppelin & Co. was the place where I get to know the AK70 for the first time, just a few days before its official launch date in Singapore, on 9th of July 2016. To be honest, I didn’t give much attention to it at that time, as besides the small size, there isn't any other feature that grabbed my attention. And my main interest during the event was the AK T8iE Mk2 that I'm currently reviewing. After the launch event, I approached SKM Technologies to loan AK T8iE Mk2 for review, and they generously loan me both AK T8iE Mk2 and AK70. And I'm glad they did. I gave it a try and use it almost daily for more than a month now. Going from Onkyo DP-X1 to AK70, I immediately realized how comfortable it is to have a small DAP in my pocket. And most important, AK70 does sound great.


Premium build quality and small size.
Balanced 2.5mm output.
USB DAC function.
Driverless USB DAC (UAC 1.0).
USB Host function for connection to external USB DAC.
exFAT and 200 GB micro SD card compatible.
AK Connect and playback from DLNA 1.0 servers.

Semi-sharp corners. Protective case is not included by default.
No sampling frequency and battery indicator when used as USB DAC.
On firmware version 1.10, Gapless playback and Equalizer don't work. EQ only reduced the overall volume by around 5 dB but doesn't do the equalization. Hopefully AK will fix it soon.

Suggestions for improvements:
To include protective case as default accessories (like AK300).
To support both USB Audio Class 1.0 and 2.0. UAC 1.0 for simple driverless operation, and UAC 2.0 to make full use of the capability of the CS4398 DAC. Selectable in the menu.
Battery and sampling frequency indicator in USB DAC mode.


Generally, AK DAPs are in the higher price category, and to simply comparing technical specifications per dollars with other brands DAP might not do justice. There are features that need real life experience to be appreciated, and many of those are not on written specification. I spent more than a month with AK70, putting many things into consideration to give it a proper rating. Besides the sound quality, all factors that are affecting the overall user’s experience are also must be taken into accounts, such as build quality, user interface, storage, playback compatibility, and many others. On one hand, I have cheaper DAPs that don’t sound inferior to the more expensive AK70, but may not have the premium build quality and excellent touch screen user interface. On the other hand, some experiences with other more expensive DAPs that in my opinion, AK70 is able to compete quite well with them. Putting all that into consideration, I’m juggling between 4.0 to 4.5 stars for weeks. When looking to options of cheaper DAPs that may sound equally good, I tend to give it 4 stars. But when comparing to more expensive DAPs and the ability of AK70 to competes well with them, I tend to give it 4.5 stars. At the end, I decided with 4.5 stars, especially considering such a bold and engaging sound from such a small player is quite an enjoyable experience. Besides that the USB host and USB DAC features that I found to be very useful. My Onkyo DP-X1 has only USB host feature but not USB DAC. While my other DAPs have only USB DAC feature but not USB host. IMHO having both features in one small DAP deserve an increase in the overall score. In other words, this small little player really packs quite a punch.


Sound Quality

Neutral, smooth, refined, bold, and engaging are probably best described AK70 sound signature. The bold and engaging dynamic is what I love most from AK70, and that what makes it sounds musical and never sounded boring or flat. I would describe AK70 sound signature as pretty close to neutral, slightly south towards good bass and smooth treble. AK70 is definitely not an analytical sounding DAP, but not particularly warm sounding either. Probably smooth sounding is the better description.

When observing my Onkyo DP-X1, after going through my test tracks for days using my reference IEMs, I got the impression of its sound signature as a tad dark, smooth, and laid-back. Some of the analytical IEMs that I have sounded rather pleasing on DP-X1, match well with its smooth sonic signature. But after going through the same process on AK70, it was harder for me to hear any obvious sonic character. The test tracks were all sounded musical and enjoyable. Bass and midrange sound full bodied with good tonal density and dynamic. Treble is smooth and never sounded harsh or analytical. As mentioned before, the engaging dynamic is probably the most addictive sound character of AK70. Dynamic is lively and engaging without being aggressive. It has a good driving capability that gives the impression of good dynamic on all IEMs that I tried with it. Between the Onkyo DP-X1 and iBasso DX90 that I’m familiar with, AK70 sonic signature is actually closer to DP-X1 than DX90. Probably the smooth treble that is quite similar to DP-X1, but with a more forward presentation than the laid-back DP-X1.


Perceived level of detail and clarity are good but not emphasized, and not as vivid as for example iBasso DX90 or Chord Mojo, that in comparison have better-perceived transparency and sound a little more analytical than AK70. Probably the smooth treble might reduce the perceived detail and transparency a little bit, but it makes AK70 non-fatiguing for long listening sessions. The smooth treble also makes AK70 have a good synergy with analytical sounding IEMs such as my DUNU DN-2000 and DN-2000J. The smooth treble and the bold dynamic is actually a good recipe for vocal. Vocal sounds smooth, lush, intimate, and full bodied. As expected from the above description, AK70 might not be an outstanding DAP for perceived detail and instrument separation as it is not an analytical DAP, but perceived detail and instrument separation are pretty good and definitely not lacking. Only not emphasized, but not lacking.

As mentioned earlier, AK70 has rather forward presentation in comparison to other laid-back sounding DAP such as DP-X1. I’m not really sure if this forward and lively dynamic can be attributed to the CS4398 DAC chip that is used in AK70. I observed that some other DAPs and DACs with CS4398 also tend to have similar forward and energetic presentation as AK70. To me, I do prefer the energetic and engaging dynamic rather than the polite one.

In summary, AK70 is an excellent all-rounder DAP that treats all kinds of recordings and musical genres equally well. It might not excel on certain recording or genre, but it performs really well for all.


In this comparisons, my approach is more to point out differences, rather than to pick which is the best. Sometimes what best for me is not necessarily what's best for others so that approach to a certain extent is rather subjective. For this comparisons, I compared AK70 with my own Onkyo DP-X1, iBasso DX90, and Chord Mojo DAC. Cayin i5 and Cowon Plenue S shown in the picture are only for size comparison. The i5 and Plenue S were belong to my brother and I didn’t have enough time with them to do a proper comparison with AK70. As with Fiio X3 2nd gen, though I think at ⅓ rd of the AK70 price, it is not too far inferior to AK70, but it is in a different price category, and AK70 with its bolder sound and dynamic does sound more engaging than Fiio X3 2nd gen. Size wise, AK70 is pretty close to Fiio X3 2nd gen, same height, slightly wider, and thinner. I also compared it with AK300, in 4 visits to Zeppelin. So not a short 15-30 mins comparison, but quite an intensive one. The summary is, as mentioned above, AK70 sounds closer to DP-X1, but with a more forward presentation. And in comparison to AK70, the AK300, DX90, and Mojo are all, in various degree, have higher perceived transparency.

Chord Mojo
Mojo is more transparent and resolving, with slightly brighter treble. I hear AK70 treble as a tad smoother and more rounded, and can be more pleasant on bright IEMs. But the smoother treble also reduces the perceived micro detail a little bit and brings the whole presentation slightly to the smoother side. Mojo performs better in dynamic and perceived detail sounds livelier with a more spacious soundstage. Overall sound quality, in my opinion, Mojo is better, but not a night and day different. Generally, AK70 sounds slightly less bright while Mojo sounds more transparent, resolving and livelier. But to be honest, after using AK70 as USB DAC for hours in the office, for many days, I honestly enjoyed AK70 and don't miss anything much from Mojo. AK70 is proven to function as a very good sounding USB DAC as well.

iBasso DX90
DX90 with the digital filter set to Slow Roll-Off has higher perceived clarity with more vivid presentation and sparkling treble than AK70. A little faster, aggressive, dryer, more authoritative, with slightly more oomph. While AK70 sounds smoother and more refined. In this setting, DX90 is more suitable for organic sounding IEMs, and might be a bit fatiguing for analytical IEMs. For example, I prefer to pair DUNU DN-2000 and DN-2000J with AK70 rather than DX90. While for AK T8iE Mk2, I sometimes prefer the DX90. Setting the digital filter set to Sharp Roll-Off makes DX90 sounds closer to AK70. Treble is less aggressive, but still, has slightly higher perceived clarity, slightly grainier treble, than the smoother sounding AK70. AK70 sounds smoother and more refined overall, but other might prefer the DX90 for more clarity and authoritative character. In my opinion, it all boils down to proper pairing and personal preferences.

Onkyo DP-X1 (Digital filter set to ‘Short’, no oversampling)
While the differences between DX90 and AK70 are quite noticeable, the differences with DP-X1 is less obvious. DP-X1 overall sounds a tad smoother and more laid-back. DP-X1 also has slightly wider soundstage. AK70 has a more forward in presentation, and doesn’t give the impression of the wide soundstage of DP-X1, but surely AK70 doesn’t sound congested in any way. I think it is the laid-back signature of DP-X1 that might give the impression of a wider soundstage. Sometimes I prefer the forward presentation of AK70 over the laid-back presentation of the DP-X1, depending on recordings. DP-X1 does sound a little smoother and refined, but sometimes that smooth and refined sonic character may sound a little artificial, and the AK70 generally sounds more realistic and natural.

Tonality, dynamic, clarity, and detail retrieval are more or less the same, both are non-analytical sounding DAPs. Transparency is good, but definitely not emphasized. In my opinion, AK70 competes quite well with DP-X1 sound quality wise.

Astell&Kern AK300
This is where things get kinda fun and interesting. Initially, I didn’t get a good impression of AK300. The dynamic sounded a bit flat for my taste, not as engaging as AK70. But with more comparisons, I got better impressions for AK300, and it doesn't sound as flat as I thought earlier. That’s why I usually doubt my first impression, as sometimes it is not very accurate. I prefer to hear audio gears in several sessions for more accurate impressions.
Matching the output volume before comparison

As mentioned earlier, I did compare AK70 and AK300 in 4 visits to Zeppelin. In the fourth visit, I brought a DIY switcher, to connect both the DAPs and easily switch the earphone connections between the DAPs. A few friends participated in a so-called blind test since they don’t know the association of the switch position to which DAP. The result is quite a balance between who prefer AK70 and AK300. Most said it is depending on the songs. The summary of the test are:
  1. The sonic differences between AK70 and AK300 are pretty small, and it was not easy to identify during the comparison test using the switcher.
  2. For some songs, AK70 might sound preferable while for other songs AK300 was preferable.

The result was almost a tie. In summary, AK300 sounds a little more transparent with slightly better in perceived detail and instrument separation, but AK70 has slightly more punch and engaging dynamic that easily connect users with the music emotionally. I’m not going to say the AK300 is easily a better DAP than AK70 because it has higher model grade and more expensive. But in this case, it is really depending on personal preferences and the IEM we use with it. To me, personally, I slightly prefer AK70.

A friend of mine, I called him WB, recently was looking for a DAP, and he spent some time in Zeppelin to compare the AK70 and AK300 as both are within his budget. After some intensive comparison, he chose AK300 as he found the sonic character of AK300 matches very well with his music and IEM. This is his comment about AK300:

“AK300 has a warm vocal and more often than not a lot of warm sound signature DAP sacrifices detail and transparency but not the AK300. I agree it lacks the punch and the dynamics but the smoothness will sometimes send you lost within the music.”

I think it makes sense for Astell&Kern to offer various DAPs with different sonic signatures to meet customer various sonic preferences. Therefore I see AK70 and AK300 as a good offering from AK to cater different sonic preferences.

Firmware Version1.10Firmware version when tested.
DACCirrus Logic CS4398 (single)Official Specification
PCM16 & 24 bits, 44.1kHz - 384kHzTested all sampling rates from 44.1kHz to 352.8kHz
DSD2.8MHz & 5.6MHzTested DSD 2.8MHz & 5.6MHz
Tested File FormatsPCM: AAC, AIFF, APE, FLAC, MP3, OGG, WAV, & WMA
CD & SACD Image FileNot compatible 
Gapless PlaybackAvailable in system setting, but not working in FW 1.1. 
Internal Storage64GB (56.52GB usable) 
External Storagemicro SD, both FAT32 and exFAT supported 
Tested Max. External Storage CapacitySanDisk Ultra 200GB Micro SD (SDSDQUAN-200G-G4A)The 200GB mSD formatted to exFAT.
USB OTG StorageNo 
Dedicated Line OutputNo 
Balanced Headphone OutputYes, 2.5mm TRRS. 
Digital OutputUSB Host 
USB DACYes, but limited to USB Audio Class 1.0 (Max 24bit 96kHz)Only support PCM from 44.1k to 96k. 88.2k is supported
USB Host for Ext. DACYes 
Selectable Digital FilterNo 
Earphone Inline RemoteNot compatible 
Hibernation / Sleep ModeYes 
Line Output Vrms2.25 Vrms 
Unbalanced Headphone Out Max Vrms2.25 Vrms 
Unbalanced Headphone Out Max Irms34 mA 
Unbalanced Headphone Out Max Power37 mW at 32 ohms
17 mW at 300 ohms
Unbalanced Headphone Out ImpedanceSpec: 2 ohms
Measured: 3.7 ohms
Unbalanced Headphone Out Perceived Hiss NoiseLow,
practically unnoticeable.
Estimated, based on observation while playing
silent tracks, using 1965 Ears V3 IEM.
Balanced Headphone Out Max Vrms2.25 Vrms 
Balanced Headphone Out Max Irms71 mA 
Balanced Headphone Out Max Power161 mW at 32 ohms
17 mW at 300 ohms
Balanced Headphone Out ImpedanceSpec: 1 ohm
Measured: 10.7 ohms
Balanced Headphone Out Perceived Hiss NoiseVery low,
practically unnoticeable.
Estimated, based on observation while playing
silent tracks, using 1965 Ears V3 IEM.
EMI RejectionExcellent, practically no experience of audible EMI noise when placing the player side by side with smartphone.Estimation, based on comparison to other DAPs.
Estimated Start-Up Time~ 22 secs to main menu.
Media scanning for 200 GB mSD with 2592 files finish at around 3:23', measured from start.
Starting from pressing the power button. Media scanning time varies depending on the amount of files and mSD read speed.
Battery Capacity2,200mAh 3.7V Li-Polymer BatteryOfficial Specification
Maximum Playback Time9 hours 44 minutesHO @ 100 mV rms, driving 16 ohms IEM, Screen Off.
Maximum Battery Charging Time5 hours 11 minutes0% to 100% shown by charging graph.

Observation of features and functionalities is based on firmware version 1.10. When I received it, AK70 was running older firmware, version 0.63. Upgrade to 1.10 was done conveniently through wifi (158 MB download size).


Build and UI
As expected from AK DAP, build quality is premium. Excellent quality metal casing with the premium workmanship. AK70 is designed with a premium feel, with nice and responsive touch screen. UI is simple and user-friendly.  


In my opinion, since it has some corners that might scratch other items when putting it together in a bag, I think AK should have included a free protective case with AK70 as default accessories, just like AK300.

Volume control and other buttons work when the screen is off. But in USB DAC mode, volume control doesn’t work when the screen is off. Need to on the screen to adjust the volume in USB DAC mode. I don't see any setting in the menu to change this behavior.


File browser is available. I consider file browser is a highly important feature on any DAP, as sometimes our music files are not properly tagged. The automatic playlist is rather limited to only 'Most Played' and 'Recently Added'. I wish to see more automatic playlist like 'Recently Played', 'Recently Played Albums', and 'Most Played Albums'.


The touch screen is responsive with a good quality display. I just feel that the battery indicator at the top is rather too small for my old eyes. Besides that, the design of the user interface is really good and user-friendly. Navigation was also smooth and easy.

The following are some settings available in the settings menu:


File Formats
AK70 plays all common file formats. I tested the following, all were playable:


The following FLAC files with different sampling frequencies were tested, all were playable:


AK70 doesn't support any format of CD image and SACD ISO image:


Both FAT32 and exFAT formats are supported.
Maximum tested working capacity: 200GB Sandisk mSD formatted to exFAT.

USB DAC & Host (OTG)


For a small player such as AK70, to support both USB DAC function as well as USB host / OTG for connection with external USB DAC, is simply awesome. Although the USB DAC supporting only UAC 1.0, but 88.2 kHz playback is supported using Foobar WASAPI driver. Otherwise, the Windows driver doesn't support 88.2 kHz. WASAPI (event) so far not very compatible with AK70, therefore WASAPI (push) is recommended for AK70 when using foobar.


My concern in USB DAC mode is the absence of battery indicator and sampling frequency indicator. In USB DAC mode, AK70 charges its internal battery slowly, taking the power from computer USB port, approximately 520 mA.


In order to activate the USB Host / OTG function, the USB icon in the drop down menu must be activated:


I have tried some USB DACs with AK70, and so far the compatibility is quite amazing. From all the USB DACs that I tested with AK70, only Mytek Stereo 192-DSD that was not compatible. Other USB DACs I tested so far mostly compatible. DSD streaming to external USB DACs also works well. USB DACs that I've tested and compatible with AK70:

Chord Dave
Chord TT
Chord Mojo
ifi micro iDSD
Light Harmonic Geek Pulse XFi


When used as USB host, connected to an external USB DAC, There is an automatic switch, where AK70 disconnects the audio streaming to the USB DAC when AK70 headphone output is connected. So we cannot use the AK70 built-in headphone output together with the external USB DAC at the same time.

Headphone Output
AK70 has balanced 2.5mm TRRS headphone output besides the unbalanced 3.5mm TRS headphone output. Both headphone outputs have similar maximum output voltage / loudness. The difference is the balanced headphone output provide higher current for a more demanding IEMs or headphone.

Maximum power output is defined as highest power output with THD less than 1%. To estimate the maximum output voltage before the waveform gets distorted, I visually monitor the waveform on the oscilloscope and monitor the FFT window to check that the harmonic distortion is less than 40 dB (100 times) from the main frequency.

Average maximum headphone output voltage
2.25 Vrms at 600 ohms load


Maximum unbalanced headphone output voltage and current
0.51 Vrms at 15 ohms load
Max output current: 34 mA


Calculated maximum power of unbalanced headphone output:
37 mW at 32 ohms
17 mW at 300 ohms

Maximum balanced headphone output voltage and current
1.06 Vrms at 15 ohms load
Max output current: 71 mA

Calculated maximum power of balanced headphone output:
161 mW at 32 ohms
17 mW at 300 ohms

Measured headphone output impedance:
Unbalanced: ≈ 3.7 ohms
Balanced: ≈ 10.7 ohms

Please take note that the headphone output impedance measurement result is quite far from the AK70 specification on its website. There might be some error in my measurement that I'm not aware of, but that's the result that I got.
The balanced headphone output has significantly more power than the unbalanced headphone output, and recommended for a more difficult to drive earphones or headphones.

RMAA Test of The Unbalanced Headphone Output


RMAA test is not an absolute test, and dependent on the quality of the audio interface used for the measurement. In most cases, RMAA test is only useful for verification purposes of the audio quality within the 20Hz to 20 kHz frequency range.

HRT LineStreamer+ audio interface that I used for RMAA measurement has the following specification:
Frequency Response (20 Hz/20 kHz)  : +0 / -0.4 dB
S/N Ratio (DC to 30 kHz) : 104 dB
S/N Ratio (A-weighted) : 109 dB

That means A-weighted S/N measurement result won't be higher than 109 dB (with a few dB tolerance), even if the audio equipment has better than 109 dB S/N ratio. AK70 Signal to Noise Ratio is rated at 116 dB. Due to the limitation of the audio interface, RMAA S/N result won't be showing measurement result that is better than 109 dB.
We can see from the RMAA result below which was done at 96 kHz sampling frequency, the result are good and within expectation.

RMAA Test Result:
[MME] AK70 HO @ 24bit-96kHz
Frequency response (from 40 Hz to 15 kHz), dB:
+0.00, -0.01​
Noise level, dB (A):
Dynamic range, dB (A):
THD, %:
IMD + Noise, %:
Stereo crosstalk, dB:


Noise and EMI Immunity
Headphone output hiss noise is practically very low, both on unbalanced and balanced output. For hiss noise test, 1964 Ears V3 is my most sensitive IEM that picks up hiss noise from practically any headphone output. It is more sensitive than other IEMs that I have, and even more sensitive than my sensitive DUNU hybrids IEM, DN-2000 and DN-2000J, that are among sensitive IEMs that easily pick up hiss noise.
Practically I would say that AK70 headphone outputs are very quiet, no audible hiss noise on most IEMs. Only when I purposely observing the hiss noise in a very quiet room, playing a silent track to enable the headphone output (disconnected when music stop), and then plugging and unplugging 1964 V3 to observe the hiss noise, than I was able to observe a very soft hiss noise on both unbalanced and balanced output. Very very soft hiss noise that is practically unnoticeable on regular use. The balanced output is slightly cleaner than the unbalanced output.
For those who has some experienced monitoring audio signal on oscilloscope might notice that sine wave signal shown in previous oscilloscope screenshots doesn’t look very clean, and the line is slightly thicker than expected. AK70 headphone output does have some noise, but non-audible high frequency noise above 100 kHz. This probably related to their noise shaping algorithm. Nothing to worry about this high frequency noise, as it is practically not audible and RMAA test showing good result of S/N test on audible frequency range. My Owon oscilloscope is a 100 MHz oscilloscope, therefore it picks up any high frequency noise beyond audio band.
I did EMI immunity test on AK70, similar test as shown in this video:
The video was made when I reviewed Fiio X3 2nd generation, to show the different level of EMI immunity from various DAPs. I’m glad to find out that AK70 EMI immunity is excellent! Practically I didn’t hear any EMI noise during the test, or when I hold the AK70 side by side with my smartphone daily.

Line Output
Line output shares the same port as the 3.5mm headphone output. It can be enabled from the setting. Line output seems no different than headphone output locked at maximum volume. The reason for saying this is I didn’t see any changes to the output impedance, with and without the line out enabled. The output impedance was observed using 600 ohms dummy load and the peak to peak voltage on the oscilloscope. Line output generally has higher output impedance than headphone output, so if line output mode bypasses the headphone amplifier, an increase in output impedance can be observed. But in this case, the output level is the same between headphone output set at max volume (150) and line output enabled. So I assume the line output mode in AK70 is no different than headphone output at maximum volume.

The 2,200mAh 3.7V internal Li-Polymer Battery practically provides more or less 8 hours of play time.
The battery test that I did was continuous playing of my burn-in track which is a compilation of various recordings, at around 100 mV rms volume level, on a 16 ohms IEM (JVC HA-FXC80), with the screen off. The IEM is coupled to a microphone that is connected to a smartphone to measure and log the microphone output level. The AK70 battery, from fully charged, last around 9 hours and 44 minutes on continuous play test.
The screen draws approximately 165 mA, therefore quite a significant load for the battery. In practical use with the occasional use of the screen, we can expect more or less 8 hours of play time, depending on the screen usage.
I’ve tested a few USB chargers with AK70, from old regular charger to the modern smart charger (QC 2.0), and the result are more or less the same. AK70 in off state, battery charging draws a maximum of 912 mA from the charger. So any 1A USB charger is sufficient, and higher capacity charger like 2A or 2.4A charger won’t make it charge faster. From completely empty, 0% battery, to fully charged, it takes around 5 hours and 11 minutes. But the battery indicator showing fully charged slightly earlier, after around 3 hours of charging. As we know, Li-Polymer or Li-Ion battery will degrade faster when left completely discharged for too long, or left charged in the state of fully charged for a long period. Best is to let the battery operates in the middle, more or less between 30% to 90% of the battery capacity, for longer service life. So it is actually preferable for the battery indicator to give ‘fully charged’ indication a bit early.
When the battery is fully charged, AK70 still draw around 212 mA from the charger for an indefinite time. This is probably to operate the charging circuit and main processor to monitor the charging process. 212 mA is actually rather high for a simple device like a DAP. For example, my Onkyo DP-X1 only draws around 150 mA when the battery is fully charged. The 212 mA draws by AK70 keeps the device a little warm when connected to a charger, but there is nothing to worry about.
(Added 10 September 2016)
Today I tried the Bluetooth feature with Creative Roar 2 bluetooth speaker, Bluetooth streaming was smooth up to around 5 meters distance, line of sight.

AK70 is probably the first AK player that I will put on my recommendation list. I was rather skeptical to AK DAPs before, especially when considering the price. AK70 has definitely changed my perception towards AK DAPs. It is truly a nice sounding little player that amazed me with its bold and engaging sound. When someone asks for a recommendation for sub $1k DAP, AK70 would definitely be among the top on my recommendation list. Kudos Astell&Kern!
And once again, many thanks to SKM Technologies Singapore and Zeppelin & Co. !

Equipment used in this review:

Earphones / IEMs & Headphone:
1964 Ears V3
AK T8iE Mk2
DUNU DN-2000
Jomo 4
Kennerton Odin

DAPs & DACs:
Chord Dave
Chord Mojo
Chord TT
Fiio X3 2nd gen
iBasso DX90
Light Harmonic Geek Pulse XFi
Onkyo DP-X1
ifi micro iDSD
Mytek Stereo192-DSD

Measurement Instrument & ADC:
Amprobe Pocket Meter PM51A
Owon VDS3102 Digital Storage Oscilloscope
HRT LineStreamer+
ZKE EBD USB+ (Battery Capacity Tester)

Some recordings used in this review:
i own the DX90 and a Arcam IRDAC, need something different, I use the 1964 V6S, Sonic Gr07,vc2000 and a sony 1rmk2 for portable stuff. 
is the ak70 something equal in sonic qualities and would provide something different. ?
Great review. 
Hi I want to use one of these as main /source digital audio player all in one combined with ripping on my cd's so basically my entire music library but want to use my own DAC Mytek brooklyn but want to know of the compatibility of the usb connection can someone elaborate on this as the internet has not been helpful and the review brushed on it very briefly with a specific connection or cable type?. My theory micro usb from DAP into the DAC with usb C connection (printer connection)?