Design.

The exterior design of N3U is just a slightly scaled-up version of N3Pro, still resembling their N6ii, especially around the volume wheel and hardware playback control buttons.  Due to a larger display and repositioning of the tubes, as expected, N3U will be slightly longer than N3Pro.  N3U’s overall size of 125×65.5×19.5mm, and the weight is 204g, just 9g more than N3Pro.  I still find it to be compact and pocket-friendly, making it very comfortable to hold and operate in one hand and being able to easily reach across the touch screen with a thumb even if you have an average or smaller size hand.  And overall, it does feel solid.

And speaking of the touch screen, the size went up from 3.2” IPS to 4.1” TFT multi-touch screen with a higher 720×1280 resolution in comparison to N3Pro.  The whole top surface is glass, and only a 4.1” area is allocated for the touch display.  At the bottom, you have a round touch LED Home button which also has the functionality to change LED color depending on a sample rate of played file or when charging.  The light could be disabled in Settings.  The back of the N3U seems to be glass as well, while the chassis frame is metal.  At the top, you will find a dedicated power (long press) and screen on/off (short press) button, unlike N3Pro where the volume wheel also had power button functionality.  The left side has a spring-loaded slot for a microSD card, the only internal storage option for N3U, or you can add OTG external storage as long as it doesn’t draw more than 300mA of current.  Below the microSD card, there are two small perforated (laser-drilled) windows with tubes underneath and a glowing amber light with the help of the backlight LEDs.

The right side of the N3U is very similar to the N3Pro.  You will find a volume wheel at the top, slightly recessed so it becomes surrounded by top/bottom guards.  As it was already mentioned, the wheel is for volume only, and no longer doubles as a power button, so it feels more solid and less wobbly.  It is not super tight, allowing easy control with just a thumb when you roll it up/down from the front or the back to change the volume.  There is a click-feedback as you turn it with every step.  Below the volume/power wheel, you will find 3 playback control buttons, comfortably spaced even for fat fingers, where you have Play/Pause in the middle and Skip/Forward at the top and bottom.  While the chassis of N3U is all black, the volume wheel and buttons are golden, but it has a muted golden tone, not too much bling-bling in your face.

All the ports are located at the bottom of N3U.  Multi-function USB-C port supports charging, file management, USB DAC, and digital Transport, as well as embedded SPDIF Out using the optional cable to bring out Coax output.  Then, you have a dedicated 3.5mm SE Line Out with a selectable output voltage of 2.1/1.6/1.0V corresponding to High/Mid/Low in Settings.  Next to it is SE 3.5mm Phone output which you select as either SS or Tube in Settings and change the gain between H/M/L.  Unlike N3Pro where Tube output was only from 3.5mm, N3U 4.4mm BAL output can be selected between SS and Tube, and it is still shared between Phone output (H/M/L gain) or BAL Line Out which also has a selectable voltage level of 4.2/3.2/2.0V corresponding to High/Mid/Low in Settings.  Due to the smaller footprint of N3x DAPs, there is not enough room for a second dedicated 4.4mm port.

Under the hood.

In the heart of N3U you have a newer dual AKM Velvet Sound AK4493SEQ DAC (each in mono mode), with playback support of all the popular lossy and lossless audio file formats, including PCM decoded up to 32bit/768kHz, handling DSD up to DSD512 and even SACD-ISO, an update in max sampling rate over the original N3Pro.  Since no internal storage is offered, you will have to use microSD cards which are constantly dropping in price.  Plus, you can connect additional storage via USB OTG, just make sure it doesn’t draw more than 300mA of current.

As previously mentioned, the display went up in size and resolution, up to a 4.1” (720×1280) TFT multi-point touch screen.  It is still nothing special by today’s smartphone standard, but considering it’s not intended for apps or video playback, this is more than adequate and makes it easier to navigate the controls and settings.  I’m not too picky about the quality of embedded artwork, so I have no complaints here.  Also, while using N3U outdoors, I had to bump the brightness slightly higher, though I never needed to go to the max.

Considering its compact size, the battery capacity of 4500mAh (3.85V) is not bad, even a bit higher than N3Pro, and in my absolute worst-case scenario testing, I was able to get 7hrs 45min playing hi-res files in a loop from 4.4mm BAL output with med gain in Classic Tube mode.  According to Cayin, as a best-case scenario, you can get up to 11.8hrs of playback from 3.5mm in SS and up to 9.7hrs of playback from 4.4mm in SS.  When it is time to recharge, you can take advantage of fast QC3.0 charging which can recharge the battery from 20-80% in about 1 hour.

The headphone output spec is decent as well with 4.4mm BAL (1ohm output impedance) being able to output up to 600mW into 32ohm load, while 3.5mm SE (0.6ohm impedance) scaling it down to 250mW @32ohm, in both cases the same for Solid State and Tube outputs.  I will cover various IEM and headphone pair-up examples further in the review so you can get a better idea of how these numbers translate into the actual performance relative to the gain setting and the listening volume level.

Unlike N3Pro, N3U doesn’t have any wireless connection, no wi-fi for OTA fw updates (or streaming apps), or Bluetooth for wireless audio transmission.  Cayin made this decision because they wanted pure audio performance without any RF interference coupling into tubes which are prone to that.  There is no way around it, vacuum tubes are extremely sensitive to wireless interference.  I read that some people expressed concerns due to their dependency on streaming instead of the local file playback.  For those, you can use N3U as a USB-DAC connected to your laptop or think of N3U as a wired dongle with your smartphone without worrying about draining your phone’s battery since it has a built-in battery.

What makes N3U, just like N3Pro, stand out from other DAPs in a similar price range is the triple timbre design of using either Solid State or Tube (JAN6418) with two different modes.  According to Cayin, they have changed the application of the JAN6418 in the N3U circuit by using it as a low-gain voltage amplification device and incorporating a hardware analog volume controller to suppress the inherent noise of the tube.  Furthermore, Cayin refers to this part of the circuit as Timbre Selection, user-selectable from either a 3.5mm or a 4.4mm port and applicable to both PO (headphone output) and LO (line output).

As already mentioned, the tubes used in the design are Raytheon JAN6418, vintage miniature pentode tubes, known for their low power consumption which is appropriate for portable use.  These are not considered to be very warm tubes, but have just enough to give the sound a warmth and texture which is different from the Solid-State timbre signal path.  Also, only two matched tubes are used to cover the Timbre circuit because a fully balanced design would require not only 4 matched tubes but also a doubling of the ckt around it.  The compact footprint of N3U wouldn’t be able to fit all the circuits required for a fully balanced tube output.  Also, unlike N3Pro where tube output was only available from a 3.5mm SE port, N3U handles its audio path differently through a workaround of converting Differential to SE signal before the Tube Timbre circuit, and then back to differential to be able to drive the BAL output.

Just like with any real tube, you also have to deal with the microphonics effect due to the vibration of the filament.  For that, Cayin designed a custom silicone case, suspended inside the DAP with a flexible PCB.  But in N3U it was updated with a newly designed custom-built shock absorption silicon housing that enables vertical suspended mounting based on the N8ii design.  As a result, while N3Pro did have a tube ringing when you tape or shake the DAP, N3U minimized it to be almost unnoticeable.  Btw, you still have a short wait period when switching between the modes to fully stabilize the output sound, but you no longer have to worry about the microphonics.

(Courtesy of Cayin)

Tubes by itself are not the only highlight of this design.  When you switch from SS to Tube timbre, you also have a choice of 2 Tube modes: Classic and Modern, aligning N3U with the Gen3 vacuum tube circuit design introduced in N30LE, to give you more variety in fine-tuning and coloring of the sound.  The original idea of dual Tube mode goes back to Cayin’s Dual Operation Mode which first appeared in their HA-6A desktop tube amplifier, and considering that JAN6418 are Pentode tubes, they were connected in either of those modes.  So, overall, you are getting a DAP with 3 different sound timbres: Solid State, Modern Tube, and Classic Tube.

Page 3 – GUI.
Page 4 – Sound Analysis and Pair up.
Page 5 – Comparison, Wired/Wireless connections, and Conclusion.