Fine-tubing the sound!

PROS: ability to finetune DX320 (and DX300) sound with a more natural tonality, improves soundstage expansion, 4.4mm BAL outputs, dedicated 4.4mm true LO.

CONS: additional cost of the card.

The product was provided to me free of charge for the review purpose in exchange for my honest opinion.

Manufacturer website: iBasso.  Available for sale directly or retailers like Bloom Audio (AMP4 and DX320 Edition X).

My full DX320 review here.

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Intro.

When you look at the latest iBasso DX320 flagship DAP and its spec with dual ROHM DACs, dual independent analog and digital batteries, hi-res 6.5” display, Snapdragon 660 and optimized Android 11, 6GB RAM/128GB storage, and a modular amp design with AMP11mk2 and optional AMP12 and AMP13, one might think it’s already a complete package.  That is true since you have a fast Android interface with flagship DACs and different sound flavors of AMP modules.  Introduction of DX320-X, 10^th year anniversary limited edition, was a nice touch with exclusive liquid-metal chassis.  But iBasso decided there is room for more and announced AMP14 with Korg NuTube and 4.4mm PO and LO balanced outputs.

NuTube module was already introduced in AMP13, but it was 3.5mm PO only.  Considering a number of audiophiles who switched to balanced cables, some were not too thrilled to use the adapter with their 4.4mm plugs and were excited about AMP14.  So, is this new amp module just a balanced version of AMP13 or more?  Let’s see what I found after spending the last two weeks (of 2022) testing the new iBasso AMP14 card.

Unboxing and Accessories.

Unboxing experience of AMP14 card is packed with a lot of goodies.  The product arrived in a compact cardboard box with an amp card inside of ESD bag in a hard-shell zipper storage case, screwdriver, extra set of screws, double-sided adhesive foam strip, warranty card, and a clear TPU case for the DAP.  Screws are small and easy to lose when taking the card out, thus an extra set is a welcome addition.  Hex screwdriver is important too, not everybody has a full set of hex bits.  Extra adhesive square pieces are there to replace the ones which secure NuTube module to ckt board.  And don’t discard ESD bag.  Unlike enclosed amp modules for DX150/200/220, DX3x0 and DX240 AMP cards have open printed wiring board which you need to keep in ESD bag.  Once you remove stock amp card, make sure to store it in that bag.

The included clear TPU case for DX320 actually works for both original and X models.  DX320 comes with a leather case, but it doesn’t have a cutout on the back to reveal NuTube lights.  Clear TPU case does just that, offering a bumper protection for your DAP by wrapping around the edges and the back while giving you full access to all ports including microSD card opening, and also giving you a clear view of the DAP chassis and NuTube lights window on the back.  The case will cover the hw transport buttons on the right side, but they are still easy to press.  And even so the case is designed for original DX320 chassis, it also works with a slick liquid metal X version, giving a clear view of its sexy chassis.

Please keep in mind that AMP14 comes with a faceplate for the original DX320.  If you got X version of the DAP, you will have bonus faceplates for AMP12 and AMP13, and AMP12 has two 4.4mm ports spaced the same as AMP14.  Because of that, you can use AMP12 liquid metal amp faceplate with AMP14 to convert it for use with DX320-X.  It’s a very simple procedure, just remove 2 Philips head small screws holding the faceplate attached to the printed wiring board and replace the faceplate.

Under the hood.

As it was already mentioned, AMP14 is a Korg NuTube 4.4mm Pentaconn balanced PO amp with a balanced 4.4mm true LO, compatible with both DX300 and DX320 DAPs.  And while only a single NuTube module is used here, just like in AMP13, AMP14 design utilizes a popular NuTube 6P1 as a voltage amplifier, followed by JFET differential amplifier that converts signal to L+, L-, R+, R- balanced output.  According to iBasso, they also used two JRC volume control chips to form a 4-channel true balanced volume control that passes through 4-channel balanced output opamp buffer stage going to genuine Pentaconn 4.4mm socket.  The Line Out bypasses all that, going directly to its own dedicated 4.4mm socket.  The balanced PO is 5.2Vrms, while the balanced LO output is 1.8Vrms.

Upon closer look, you will see 3 separate potentiometers on the board next to NuTube module.  iBasso calibrates each module with an audio analyzer by manually adjusting these multi-turn pots to optimize the performance of the NuTube.  Also, many are familiar with dual-battery design of DX300/320, bringing analog battery power directly to the amp card.  AMP14 takes that input power and using two Linear Tech DC-DC converters partitions it into 4 separate isolated voltage supplies for different parts of the amp card circuits.  For example, the anode of NuTube 6P1 module gets its own filtered 14V, while opamps get +/-8V for a full 16V swing.

Furthermore, with AMP13 and wifi on I heard random interference crackles when idling or between the tracks.  Under the same test conditions using the same router at home (5GHz channel) and the same distance away from the router and my phone, I hear noticeably less interference with AMP14.  I still get it occasionally with AMP14, but it is less frequent and hardly noticeable during the playback.  Most of my cables are 4.4mm BAL and I use 3.5mm adapter with AMP13, so maybe the adapter itself picks up more noise vs connecting to AMP14 directly.  Or maybe the balanced differential nature of AMP14 signals cancels it out, who knows.  But the fact still remains that I tested it for two weeks and I found a lot less interference using AMP14 vs AMP13.

Make sure you update DX300/DX320 fw to the latest version which adds AMP14 support.

Page 2 – Sound analysis and Conclusion.