Any device capable of playing sound will have a DAC and/or amplifier inside it! This includes phones, computers and noise-cancelling headphones and gaming headphones. Not all headphones have an amp though. Even if the headphone has an amp, you can vastly improve the audio quality with an external DAC amp such as the FiiO BTR3K, which is the cheapest and easiest way to upgrade the audio.
The FiiO BTR3K integrates two AK4377A2 DAC chips, as well as two standalone crystal clock oscillators (24.576 MHz and 22.579 MHz), which help keep "jitter" and "frequency drift" very low, as well as making the sound more detailed and airy.
With two high-performance AK4377A DACs, the BTR3K power output increases by 50% compared to the AK4376 used in the BTR3. The AK4377A DACs (digital-to-analog converters) convert the digital signal into an analog signal for each channel. The implementation of the dual chip DAC in the BTR3K works well, allowing it to get better channel separation and reduced crosstalk noise than the single chip DAC in the BTR3 amp.
The BTR3K can deliver 25mW of power under 32 Ohm load and 50mW under 16 Ohms load via the 3.5mm single ended output. Via the 2.5mm balanced output, the BTR3K can deliver 78mW of power under 32 Ohm load.
The signal-to-noise ratio is 122dB. The BTR3K single-ended output delivers the same power output as the single AK4376-A DAC in the BTR3. The BTR3K balanced output is able to deliver enough power to drive headphones up to 100 Ohms, loud enough. The minimum impedance rating required for headphones is 16 Ohms.
The BTR3K has polished rounded edges, a slim aluminum alloy frame and 2.5d arc glass panels on the front and back, giving the BTR3K a smartphone look. The BTR3K weighs 24 grams so, it's a touch lighter than the 25 grams BTR3 and 3 grams heavier than the BTR1K. The FiiO BTR3K circuit board has also been upgraded to a six-layer hdi printed circuit board with electroless nickel immersion gold (ENIG) surface plating.
Being made with 2.5D arc glass, the BTR3K have a curved (contoured) edge and it's also as slippery as the M5 DAP. The BTR3K does also have the same oleophobic oil-repellent coating that minimizes oily fingerprint smudges. The glass on the BTR3K is not scratch-proof though; hence you will definitely want to use the included plastic, clip-on protective case.
While the FiiO BTR3K is designed as a headphone amplifier, it can also be used as a computer DAC amplifier, although the BTR3K only supports 16-bit at 44.1kHz and 48kHz sample rates, which is the same sampling frequency supported by the BTR3.
If you need higher sample rate, it's best buying the BTR5 which supports 32-bit/384kHz and DSD256 audio.
The FiiO BTR3K is capable of driving 100 Ohm impedance headphones and uses the same CSR8675 Bluetooth chip as the BTR3 but fully supporting Bluetooth 5.0, unlike the BTR3 which only supports Bluetooth 4.2.
The BTR3K Bluetooth 5.0 version is strong and long reaching (9 meters), as well as being stable and, supporting a wide range of Bluetooth codecs, including SBC, AAC, aptX, LDAC, aptX-LL (low latency) and aptX-HD (high definition). This said, the BTR3K does not support LHDC (BTR3 does).
Most headphones/earphones do support SBC and aptX but, not all support LDAC, LHDC or the low latency and high-definition versions of aptX. Of course, to benefit from any of these codecs, your headphones have to support these codecs. Only a few handful of headphones support LHDC, including the Xiaomi Air 2 TWS Earphone and the Sennheiser IE 80 S BT.
The FiiO BTR3K does not require a mobile app to work but, you can get the most out of it when using the FiiO Music App, which integrates a tuneable 10-band Equalizer (EQ).
The FiiO Music app EQ comes with labeled frequency bands, including 2K-3K bands for tweaking the vocal midrange, as well as four sound presets (rock, pop, R&B and dance) and a customizable sound preset.
You can use other third party mobile apps with the BTR3K but, the FiiO app has a clean user interface (UI) design and no advertisements.
The FiiO app plays DSD and FLAC audio so, it's capable of producing very good sound quality with low digital noise. How good the sound is does depend on the quality of the decoding chip inside the phone the FiiO Music app is installed.
The FiiO Music app also features screen lock album art, lyrics download option and can scan local files on SD card. For a free mobile app, the FiiO app integrate a lot of parameter settings, including call volume and "car mode" which when enabled will power the BTR3K on and off when the car engine starts and stops.
A few things the FiiO app equalizer does not support include streaming audio via Spotify or YouTube, Chromecast support and automatic scanning for new music files. The BTR3K is pre-set to connect via Bluetooth by default but, you can change the priority to USB DAC mode via the FiiO app.
The buttons on the BTR3K, including the volume rocker, make a subtle but audible tapping sound. There are a total of 32 steps in the volume control of the BTR3K so, volume is increased in increments of 1 from 0 to 32. The volume buttons control the volume as well as clear current paired devices, which is useful since the BTR3K can be paired simultaneously with two devices.
There are a total of four buttons: a power button, a two-button volume rocker and a Bluetooth button, all of which control multiple functions. The power button lets you turn the BTR3K on and off, as well as reset it by holding the power button for 10 seconds. The Bluetooth button allows you to manually activate pairing mode, as well as play/pause, answer, reject and end a call.
There is a microphone built-in to the BTR3K but, in order to function with your headphones, the headphones microphone has to support the TRRS CTIA standard pinout, which most newer headphones do. However, if you have an older pair of headphones chances are the microphone supports OMTP. In which case, you will have to use a universal OMTP to CTIA adapter in order to use the BTR3K mic.
The BTR3K still uses an omnidirectional microphone with Qualcomm's cVc noise cancellation (just like the BTR3). The BTR3K microphone quality is good in most situations, although in louder environments you will have to bring the BTR3K mic closer to your mouth  or your voice will sound quieter or distorted. This is due to cVc's automatic gain control, which automatically increases the gain so, if the BTR3K microphone is too far from your mouth in a loud environment, the background noise will be amplified, leading to distortion.
The FiiO logo is also an status led that changes color to visually feedback bluetooth pairing, charging and bluetooth codec. For example, SBC (blue), ACC (cyan), aptX/aptX-LL (purple), aptXHD (yellow) and LDAC (white). The BTR3K also makes an audible beeping sound for certain functions, including bluetooth pairing, max volume and low battery.
The BRT3K internal battery has a 330mAh capacity that takes 1.5 hours to fully recharge, which is the same time it takes to charge the 300mAh battery capacity in the BTR3. While the BTR3K has a larger battery capacity, battery performance is similar to the original BTR3 - up to 10 hours play time. Long battery life will depend on other factors such as volume level, headphone port and bluetooth codec. You can expect up to 10 hours battery life via SBC and 9 hours via LDAC playback when playing on medium volume via the 3.5mm port. Up to 7 hours using AAC.
Battery life is lower when listening via the balanced 2.5mm port. The BTR3K is also equipped with a high performance low dropout (LDO) linear voltage regulator, which will help extend the lifespan of the battery when using a higher voltage input. That said, FiiO does recommend using a 5V power adapter when charging the BTR3K.
Amps and DACs can be bought individually, as a DAC/Amp stack or, as an integrated combo in the same unit like the FiiO BTR3K, which amplifies the sound, making the audio sound louder, as well as make the audio clear and more defined by decreasing noise interference (i.e. hums, hisses, etc).
Most DAC amps are bulky and connect via USB, although you can get small, wireless versions such as the FiiO BTR3K, which doubles as a neat Bluetooth DAC amp (for headphones) and USB DAC for desktop computers, mobile phones and even the Nintendo Switch.
When using the BTR3K with a phone though, you will need an OTG cable like the CL06 or LT-TC1, which are not included. This said, it's worth mentioning that not all Android phones will support connecting the BTR3K via OTG cable. The FiiO BTR3K is available to buy on amazon. See the review of the FiiO M3 Pro DAP