An (industry) player  

Founded in 2007 in Guangzhou, China, FiiO has grown from a niche purveyor of pocketable audio devices to one that offers a virtual tidal wave of gear. The company’s website shows 29 portable music players, 16 desktop digital-analog converters (DACs), 16 portable DAC/headphone amplifiers, 14 in-ear monitors, 12 USB adapters, 3 active loudspeakers, 29 audio cables, plus a host of accessories.   

FiiO is currently housed in a 15,000 square-foot office, design, and manufacturing facility in Guangzhou which it acquired in 2022. Highlighting the importance that the company attaches to acoustical measurements in its design process, the facility holds two audio precision analyzers, an anechoic chamber, and a microwave shielded room. According to FiiO, its annual production capability now exceeds 2 million units, and it can scale up to add another 2 million.  

In short, FiiO isn’t a sketchy, fly-by-night brand. Rather, it is a major player in the personal and desktop audio markets. In this review, I look at FiiO’s K13 R2R DAC/headphone amplifier ($319/all prices USD). 

Are You R2R Curious?  

Most DACs convert the digital signal via an integrated Delta-Sigma chip that’s made by companies like ESS Technology (ESS), Asahi Kasei Microdevices (AKM), Texas Instruments, and Cirrus Logic. These devices convert by oversampling, noise shaping, and filtering. Some Delta-Sigma chips work with Field Programmable Gate Array (FPGA) circuits that are customized to work with a specific product after they are manufactured. This can improve the product’s performance and allow for easy firmware updates that further improve performance and add features. 

R2R DACs use an array of binary resistors that contain the values “R” and “2R.” Each bit of the digital input controls a switch that connects either to a reference voltage or to ground, creating a current proportional to its binary weight. These currents are then summed to produce the final analog output voltage. 

R2R fans claim that, compared to chip-based converters, R2R-based ones provide a rich, organic, and non-fatiguing sound. They note that unlike Delta-Sigma converters, they use an analog signal path. Fans of chip-based DACs champion their precision, linearity, and detail. 

The K13

As you might surmise from its name, the FiiO K13 uses an R2R-based digital converter. FiiO has developed its own proprietary 24-bit R2R architecture consisting of an array of 192 thin-film resistors arranged across four channels that are said to be within a 1% performance tolerance and an ultra-low 3ppm temperature drift. 

Historically, changes in the resistors’ relative values (i.e., drift tendency) have made R2R designs economically difficult to pull off. This is because the resistors must be hand selected and matched to achieve a high-performance R2R design. However, the K13, which is the first DAC to feature FiiO’s latest R2R architecture, and the FiiO K11, are among the lowest-priced R2R DACs I’ve seen. 

The K13 features a balanced differential digital and analog circuitry. This will placate so-called experts who assert that, absent the use of truly differentially balanced circuits, balanced XLR connectors are a mere marketing tool that do not improve performance. The amplification section uses OPA1642 and TPA6120A2 chips, both dual, that deliver up to 2400mWpc into a 32-ohm load through its 4.44mm balanced output and 600mW into 32 ohms through its 6.35mm single-ended jack. Even with my hardest-to-drive headphones, the Dan Clark Stealth, there was power to spare.  

The K13 has a built-in 30W switching power supply that is shielded by a nickel-plated cover. It can also be powered via an external 12V DC power source. You have the option of adding an outboard power supply, and for my testing I used a FiiO/JADE 12V linear supply ($200) and an external capacitor bank ($90). 

The K13’s unibody, CNC-machined chassis comes in black or silver. On the chassis' top panel is a round glass window that beautifully shows off the R3R resistor array. 

Included with the K13 you’ll find the remote, AC power cord, quick start guide, warranty card, headphone adapter, and a USB data cable. Unlike many other Chinese manufacturers, FiiO provides paper owner manuals that detail all the finer points of a product’s set-up and control, and the K13’s included manual has 17 pages.  

If you want to look at the K13’s circuitry, FiiO has posted photos of most of it on its website. Unlike many old-school audiophile companies whose explanations of technical superiority begin and end with “trust us and your ears,” FiiO reveals almost every technical aspect of its product designs, including the third-party model name or number of the operational amplifiers (OP amp), capacitors, and volume controls used. (Spoiler: the K13 uses ELNA’s RA3 series capacitors.) Like all modern DACs, the FiiO K13 has Bluetooth input capability.   

The K13 EQ settings options deserve special note. Not only is there a 10-band parametric EQ, but you can make your own custom curves and save up to ten of them. You can also download other user EQ settings via the FiiO Control app or a browser-based web interface. The app lets you change the input, turn the top indicator light on and off and change its color, and turn the knob indicator light on and off and change its color, on the main screen. A separate EQ panel lets you control or turn off EQ functions. Using it, you can add 12dB or subtract 24dB from 10 separate bands (32, 64, 125, 250, 500, 1000, 2000, 4000, 8000, and 16,000Hz).  

Lastly, the Control app features the full K13 owner’s manual.   

The remote adds additional controls. These include buttons to change the input, adjust volume, change EQ settings, mute output, adjust gain levels to one of the three settings, and lower the display output level.  

Getting ready  

Since I recently used FiiO’s K9 Pro desktop DAC/amp, I still had the Control App on my phone and it instantly found and connected to the K13. Right out of the box, the K13’s primary color was a yellow green I found to be similar to bile. I therefore used the app to change it to a nice, boring blue and, since I was already oversampling through Roon, also turned off the K13’s oversampling feature.  

Another feature I turned off was the K13’s built-in EQ, since I prefer an unadjusted signal for critical listening. EQ is useful for casual listening, or to correct a problem or change the intrinsic sound of your headphones or speakers, but I don’t try to correct my gear to my own tastes. 

I briefly used the built-in power source before changing to a FiiO/Jade Audio 12V 3-amp linear power supply (“LPS”). Also, I placed a 5 to 24 volt-capable capacitor bank between the FiiO/Jade Audio LPS and the K13.   

Climbing the ladder  

I tried the K13 R2R headphone outputs with my most sensitive headphones, the Empire Ears Zeus ($2,099), and with my least sensitive headphones, the Beyerdynamic DT990 600 Ohms ($199) and Dan Clark Stealth ($4,499). There was no background hiss with the 115db-sensitive Zeus, while the K13 R2R had enough power to drive both the DT990 and the Stealth well past my own personal volume threshold.  

As mentioned above, I did not spend much time on the K13’s EQ features. But if you feel the need to radically change the harmonic character of your headphones, the K13 R2R’s extensive EQ options give you the power to change the sound in dramatic ways. In my world, if you need to extensively and religiously EQ your headphones to be happy, you bought the wrong headphones! 

I compared the K13 to Fosi Audio’s fully balanced ZD3 desktop DAC ($179), also using a FiiO/Jade outboard 12V LPS and 5-24V capacitor bank between the power supply and the DAC. Unlike the K13, the ZD3 uses Delta-Sigma modulation. The difference between the two DACs was subtle, but during extended listening sessions, the K13 R2R mustered a better recreation of depth and was less fatiguing to listen with. 

During the time I’ve had the K13 I’ve had several other high performance DACs on hand. The K13’s sonic signature is most akin to the Garlubidor Divinity DAC ($!895 MSRP), emphasizing space and dimensionality as opposed to the Imersiv D-1A DAC ($12,000 MSRP) which is much more detail oriented with excellent specificity, but slightly less dimensional expanse. While entry level priced, the K13 performs at a level that would not have been thought possible at this price as little as five years ago. 

Hard to resist  

Old-school R2R DACs can be expensive enough to dissuade someone from trying one out, and they also generally don’t measure as well as many chip-based DACs. But FiiO’s K13 DAC/headphone amp is definitely worth a try. It provided me with many hours of enjoyable, easy-to-listen to sound. Further, at $320, it is still in the “accessory” price range by today’s audiophile standards.  

FiiO K13 R2R Desktop DAC/AMP  

Price: $319.99 USD  

Warranty: one-year parts and labor

Dimensions: 1.7” H (incl. feet), 8.3” W, 7.4” D 

Weight: 2.2 lbs

Guangzhou FiiO Electronics Technology Co., Ltd. 

Guangzhou City, China 

www.fiio.com

Review sample provided by:

Apos Audio

Oakland California

www.apos.audio.com

Associated Equipment  

• Digital Software: Roon, Qobuz, Audirvana, Audirvana Studio, Apple Music,   

• Digital Sources: Gustard A-26 connected to AnCoalas Double Pi Roon endpoint, Fosi ZD3, Gustard X-16, Topping D90SE, Roon server on Intel i7 NUC, Synology DS-2024+ NAS, Raspberry P4B using Diet Pi software and a capacitor bank in power supply employed as a Roon Endpoint  

• Cables: WireWorld Series 8 30’ balanced, Kimber KCAG 1 meter, ½ meter balanced and unbalanced, Audience AU24 SE speaker cables  

• Equipment Racks: Arcici Lead Balloon 

• Listening Room: RoomTunes absorber panels, Acoustic Sciences (ASC) Tube Traps, GIK acoustics panels, ¼ inch industrial felt pad on the desktop, custom ceiling clouds and corner bass traps