Astell & Kern SP4000T

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Audio46 Purchase – SP4000T

A Little Technical Stuff:

Model: SP4000T 

• Body Color: Silver, Copper
• Body Material: Stainless Steel, Copper
• Display: 6inch 2K (2160 x 1080) touch screen
• Supported Audio Formats: WAV, FLAC, WMA, MP3, OGG, APE, AAC, ALAC, AIFF, DFF, DSF
• Sample Rate: PCM: 8kHz ~ 768kHz (8/16/24/32bits per Sample)
  DSD Native: DSD64 (1bit 2.8MHz), Stereo / DSD128 (1bit 5.6MHz), Stereo
  DSD256 (1bit 11.2MHz), Stereo / DSD512 (1bit 22.4MHz), Stereo
• Output Level: Unbalanced 4.2Vrms │ Balanced 8Vrms (Condition No Load)
• CPU: OCTA-Core
• DAC: AKM4191EQ x2 + AKM4499EX x2
• Vacuum Tube: RAYTHEON JAN6418 x4 (Quad Tube)
• Decoding: Support up to 32bit / 768kHz Bit to Bit playback
• Input: USB Type-C input (for charging & PC & MAC)
• Outputs: Unbalanced Out (3.5mm), Optical Out (3.5mm)
  Balanced Out (4.4m, only 5-pole supported)
• Wi-Fi: 802.11 a/b/g/n/ac/ax (2.4/5GHz)
• Bluetooth: V5.2 (A2DP, AVRCP, Qualcomm® aptX™ HD, LDAC, LHDC, SBC, AAC)
• Dimensions: 3.37″ (85.7mm) [W] x 5.9″ (150mm) [H] x 0.76″ (19.5mm) [D]
• Weight: About 19.9oz (565g)
• Feature Enhancements: Firmware upgrade supported (OTA)
• Operating Temperature: 0℃ ~ +40℃ (32℉ ~ 104℉)

Audio Specs 

• Frequency Response: ±0.006dB (Condition: 20Hz ~ 20kHz) Unbalanced │ ±0.006dB (Condition: 20Hz ~ 20kHz) Balanced
  ±0.06dB (Condition: 20Hz ~ 70kHz) Unbalanced │ ±0.06dB (Condition: 20Hz ~ 70kHz) Balanced
• S/N: 124dB @ 1kHz, Unbalanced │ 125dB @ 1kHz, Balanced
• Crosstalk: -136dB @ 1kHz, Unbalanced │ -145dB @ 1kHz, Balanced
• THD+N: 0.0006% @ 1kHz, Unbalanced │ 0.0004% @ 1kHz, Balanced
• IMD SMPTE: 0.0004% 800Hz 10kHz (4:1) Unbalanced │ Balanced
• Output Impedance: Unbalanced Out 3.5mm (0.7ohm) │ Balanced Out 4.4mm (1.7ohm) 

Clock Source 

• Clock Jitter: 25pS (Typ)
• Reference Clock Jitter: 200 Femto Seconds 

Storage Capacity 

• Built-in Memory: 256GB [NAND]
• External Memory: microSD x1 (Max. 1.5TB) 

Battery 

• Capacity: 7,450mAh 3.8V Li-Polymer
• Charge Time: About 5 hours (PD3.0 Charging)
• Playback Time: About 10 hours (Standard: FLAC, 16bit, 44.1kHz, Vol.80, LCD Off, Low Gain)   

-SP4000T MRSP:  $3620.00

Welcome to another review on Audio Rabbit Hole. I am starting this dialogue a full page in, after the specs, because apparently I thought everyone needed a light cardio session before getting to my actual thoughts. Holy smokes!

I want to introduce you to, or at least share my highly subjective thoughts on, the latest tubey DAP from Astell & Kern: the SP4000T. The “T” is for tubes, because subtlety apparently left the building.

Anyone who reads my reviews probably knows by now that I love the Astell & Kern house sound signature, especially in their DAPs. I have also enjoyed most of the A&K IEM collaborations I have tried, so yes, there may be a tiny bit of brand favoritism baked into this audio pastry.

The SP4000T is no different. The house sound signature is still present in all its glory, only this time you get to add some tube goodness in a dose you can control. Think seasoning, not dumping the whole spice cabinet into the soup.

For those not familiar with the A&K house signature, my subjective description would be detailed yet refined and natural, with a smooth top end. It is never harsh or in your face, which I appreciate.

I enjoyed my time with the SP4000T and would not hesitate to recommend it if you want an Astell & Kern DAP with tubes. The flagship A&K DAP is still the SP4000, which is aimed at someone seeking the flagship experience, not overly worried about price, and not looking for tubes. You cannot go wrong with the SP4000.

I have heard both and had both for a few weeks, so this is not a drive-by opinion from the parking lot. The price difference is also a factor: the SP4000 is $4,290, the copper version is $4,499, and the SP4000T comes in at a more palatable $3,620. I say “more palatable” carefully, because we are still very much dining at the expensive table.

Let’s take a closer look at the SP4000T. Keep in mind this review will include a heavy dose of subjectivity, as all good audio reviews do before the comment section starts throwing chairs.

I will say that I have heard other companies that, in my opinion, do tubes better when focusing strictly on the tube presentation. That does not mean they have a better house signature, or that they blend their house sound with tubes as well as Astell & Kern does here.

A Little Marketing Hype, straight from their site, no edits:

WHAT’S IN THE BOX:

• SP4000T
• Protective film
• Leather pouch (for IEM carrying)
• Leather case
• USB Cable
• Warranty card
• Special thanks card
• Leather Box

Unboxing and Accessories:

I am going to let the photos do most of the talking for the unboxing, but I do have a couple of comments.

First, the included storage case threw me for a loop. I am so accustomed to the traditional A&K wood box that seeing this jewelry-style case, wrapped in leather or vinyl, was a surprise. It is nice, and I am cool with it, but times, they are a changing.

Second, the Premium Shrunken Calf Leather Case deserves a shoutout. It feels excellent in the hand, has a premium texture, and gives the player the kind of grip and protection you would hope for at this level.

 Build Quality :

Having spent time with many A&K DAPs, I can say the build quality is always excellent, and the SP4000T keeps that tradition going. The design is fairly similar to the flagship SP4000, with a stainless steel chassis that feels solid and, yes, heavy. This is not a DAP I would try to pocket carry unless I wanted one side of my pants to make a break for the floor.

Aesthetically, it exudes premium. It is angular, visually stunning, and unmistakably Astell & Kern. That said, I am genuinely grateful for the luxurious included case because, without it, the player is not the most comfortable thing to hold for long sessions and is prone to fingerprints.

The controls are simple and straightforward: a volume wheel, playback buttons, and a control lock. If you have used an A&K player before, this will feel familiar. If this is your first foray into an A&K DAP, you are in for a premium treat.

The SP4000T comes with 256GB of internal storage, which is a solid start, and you can expand that with a microSD card up to 1.5TB if your music library has gotten completely out of hand.

One visual difference between the SP4000T and the SP4000 is the tube “window.” When the tubes are not being used, it stays dark. When tube or hybrid mode is active, it glows red. That said, the glow is not actually coming from the tubes; it is an LED effect. Still, it looks cool and adds a nice bit of visual theater.

Internally, there are two big changes between the SP4000T and the standard SP4000.

The first is the obvious one: tubes. The SP4000T replaces the amp section with a hybrid tube amplification setup using four JAN6418 vacuum tubes, and you can choose between tube, hybrid, or solid-state modes depending on how much flavor you want in the signal chain.

The second change is in the DAC implementation. The SP4000T uses the same DAC family as the SP4000, with the AKM4191 and AKM4499EX pairing, but not in the same configuration. The SP4000 uses a quad setup with four of each chip, while the SP4000T uses a dual setup with two of each.

Battery:

The SP4000T is one of those devices where battery life depends heavily on how you use it, which is a polite way of saying your mileage may vary and your charger should probably know where you live.

In ideal conditions, with no enhancement features running, you can get around 10 hours of playback. That sounds decent on paper, but real-world use will likely land closer to five hours once you factor in screen time, streaming, Wi-Fi, higher gain, and tube or hybrid mode. Tubes may be charming, but apparently charm has a power bill.

Charging the SP4000T to full takes about five hours, which is not exactly quick. This is not a “plug it in while you make coffee” situation unless you are roasting the beans, grinding them by hand, and opening a café. Still, given how much hardware is packed inside this thing, the charge time is understandable. The battery does seem better optimized than the standard SP4000, but it is still a DAP you will want to keep charged if you plan a long listening session.

UI:

Like the standard SP4000, the SP4000T runs on an Android-based interface, now built around Android 15 with full Google Play Store support. That means you can download Tidal, Qobuz, Spotify, Apple Music, or whatever streaming app you prefer directly to the device. No ritual sacrifice to the sideloading gods, just search, install, and listen.

Alongside the tube settings, the SP4000T includes several sound-shaping and playback technologies, including Enhanced Signal Alignment, Advanced DAR, and Astell&Kern Direct Path. That is a lot of audio alphabet soup, but at least it is the fancy kind served in a flagship bowl. I am not going to pretend every listener will spend hours A/B testing every acronym like they are defusing a bomb, but it is good to see these features included with a clear purpose instead of feeling like spec-sheet confetti.

Visually, the UI does a nice job matching the SP4000T’s futuristic design. The tube controls get their own visual flair, and when tube or hybrid mode is active, the tube window on the back lights up red.

My reviews can get a little lengthy and wordy, so if I tried to break down every single UI feature, we would never get out of here. I focused on the items I felt were most notable, so apologies if I left out a key feature that matters to you. There is a lot packed into this player, and eventually I had to stop spelunking through menus and get back to listening.

Moving on to the sound section….

I mentioned at the top of this review that the Astell & Kern house signature is still very present, and it is. Typically you can expect detail, excellent imaging, and a wide soundstage, with just a touch of softness in the highs, a little added warmth, and some sweetness in the vocals. Organic, would be a great one-word description.

The DAR settings have been included in past A&K releases, but I usually try to listen in the stock form first and then slowly integrate the extra features to see what works best for my specific use case and listening preferences. I like to know what the player is doing before I start flipping switches, like I am trying to launch a tiny audiophile spaceship.

The X-factor here is, of course, the addition of the tubes. They give you a few more ways to tweak the sound to your liking, and that flexibility is really the main reason the SP4000T feels different from the standard SP4000. You can keep things cleaner and more reference, lean into the tube flavor, or land somewhere in the middle.

The SP4000T also seems to have a little more driving authority than some of the other offerings in the A&ultima lineup. This is not going to be a portable solution for extremely hard-to-drive headphones, so nobody should expect it to replace a desktop amp and start bench-pressing Susvaras for breakfast.

That said, it does quite well with middle-of-the-road planars and high-impedance dynamic drivers. It is also very comfortable with IEMs. I used the Astell&Kern SP4000T almost exclusively with IEMs during my time with the unit, and none of my pairings showed any signs of hiss. The background was wonderfully black.

My favorite pairing, without a doubt, was the Astell&Kern / Volk Audio collaboration, the Stella. The Stella already has a wonderfully spacious and open sound with a ton of clarity, but the SP4000T in Hybrid Mode added just enough warmth and body to make the pairing feel special. The minute I heard it, I was honestly in awe. I had one of those audiophile moments where you sit there pretending you are doing serious evaluation, when really you are just smiling at expensive objects.

The three tube modes each bring their own personality. Triode gives you the most classic tube presentation, with stronger note weight and a softer edge. Ultra-Linear opens up the soundstage a bit more while still keeping some of that rounded sweetness. Pentode is the cleanest and most detailed of the tube options, but it still keeps enough of that tube character to avoid sounding sterile.

Hybrid mode is where things get especially interesting. You get to blend the tube timbre of your choice with the cleaner solid-state presentation, which gives the SP4000T more depth and flexibility.

It is basically the audio equivalent of ordering your sound with a custom spice level, except instead of mild, medium, and hot, you get Triode, Ultra-Linear, Pentode, and the sudden urge to keep switching modes for “just one more song.”

Hybrid mode actually ended up being my preference. It struck the best balance between the SP4000T’s clean, detailed solid-state foundation and the extra richness the tubes bring to the table. It gave me enough tube character to feel special without pushing the sound too far into syrup territory.

My sound impressions are based on Hybrid Mode, since that ended up being my preferred setting.

Bass has excellent weight and body. Bass guitars, lower keys, and string instruments sound dense, full-bodied, and properly grounded. It is not an exaggerated or overblown low end, but it has enough substance to keep the presentation from feeling sterile or too polite.

The mids sound natural, with excellent body, shape, and weight. Nothing feels over-exaggerated or too thick, but vocals and instruments still have a satisfying sense of presence. This is where Hybrid Mode really works for me: it adds a little warmth and humanity without turning everything into audio maple syrup.

Treble is detailed, extended, and smooth. The highs have a silky quality, where nothing comes across as sibilant, sharp, or overly aggressive. Plenty of information is up top, but it is presented with refinement rather than launched directly at your forehead.

Technically, the SP4000T performs extremely well. Detail retrieval, resolution, texture, and imaging are all at a very high level. The stage is wide and deep, with immaculate layering and enough separation to feel spacious without becoming artificial.

I want to touch on a couple of other sound tweaks and the other sound modes before moving on.

The DAR, or Digital Audio Remaster, settings have been included in past A&K releases, and they are basically Astell&Kern’s upsampling options for PCM and DSD playback. I used the DSD setting quite a bit because, to my ears, it added a little more engagement, fullness, and dynamic energy. Your ears may hear it differently, because apparently audio opinions are still not governed by one universal committee.

Op Amp mode gives you more of the stock A&K house sound I have been talking about: clean, balanced, precise, and refined. It has that familiar Astell&Kern clarity without getting overly sharp or sterile. Tube mode, on the other hand, adds more weight and overall warmth to the signature. The sound becomes a little fuller, a little richer, and a little more relaxed around the edges.

Hybrid mode, my personal favorite, gave me the best of both worlds. I got enough of that clean A&K detail and control, but with just enough tube texture to make the presentation feel more engaging. Basically, it lets the player wear a lab coat and a smoking jacket at the same time.

You might want to own the A&K SP4000T if:

+ You want the Astell&Kern house sound with a little tube seasoning sprinkled on top, because apparently clean, detailed, and refined was not already enough trouble for your wallet.

+ You like being able to switch between solid-state, tube, and hybrid modes depending on your gear, your mood, and how deep into the audiophile rabbit hole you feel like falling that day.

+ You want Hybrid Mode to do the heavy lifting, giving you the clean A&K foundation with enough tube richness to feel special without turning everything into audio pancake syrup.

+ You use IEMs, easier-driving planars, or high-impedance dynamic headphones and want a black background, strong technical performance, and enough driving authority to impress without pretending this thing is a desktop amp in witness protection.

+ You are comfortable with a gorgeous, heavy, premium DAP that sounds fantastic, costs serious money, and may require you to maintain a close personal relationship with a charger.

In Closing:

In closing, I enjoyed my time with the Astell&Kern SP4000T quite a bit. It keeps the familiar A&K house sound intact: clean, detailed, refined, and wonderfully spacious, but adds enough tube flavor to make the experience feel more flexible and just a little more dangerous for anyone who enjoys tweaking things.

Hybrid Mode ended up being my personal sweet spot because it gave me the best balance of solid-state control and tube richness without turning the whole presentation into warm audio pudding.

This is still a premium, heavy, expensive DAP with battery life that will occasionally remind you that tubes, Android, and audiophile ambition all expect to be fed. It is not the player I would buy if I wanted the absolute longest runtime, the lightest pocket carry, or a portable solution for impossible-to-drive headphones.

That said, if you already enjoy the Astell&Kern house sound and want the option to season it with tubes, the SP4000T makes a lot of sense.

It gives you a gorgeous build, a smooth Android-based UI with Google Play Store support, excellent technical performance, and enough sound-shaping flexibility to keep you happily lost in menus for longer than you originally planned.

I would not call it a value product because, well, look at the price tag. But as a high-end A&K DAP with tubes, personality, and real sonic flexibility, the SP4000T is very easy for me to recommend.