More and more newer smartphones are being made without an analog output, resulting in having to use a dongle for wired listening. Problem is most USB-C to 3.5mm dongles aren't all that good performance-wise, which makes getting a portable dac amp all much the better. Portable dac amps range from full size desktop solutions to very small ones like the Hidizs S3 Pro, which has a footprint comparable to a microSD card and supports mic input (not all dacs do).

The Hidizs S3 Pro has no buttons so, it's a "plug and play" device in the truest sense of the word. The S3 Pro has an aluminium alloy gun metal finish construction made with a CNC injection moulding machine. The front and back panels are textured with circular grooves like an LP record, while the perimeter has a smooth, matte finish. The Hidizs S3 Pro is 1cm thick with a 2cm diameter size. The S3 Pro amp dac is attached to a USB-C metal plug connector via a 5cm long cable. Total length of the S3 Pro (including the litz cable) it's 9cm long. The total weight is 7 grams, making the S3 Pro as lightweight as a pair of true wireless earbuds.
The S3 Pro amp dac has a single-ended 3.5mm port that supports 55mW output at 32 ohms, which means the S3 Pro is more suited for low/medium impedance headphones for optimal bass. The built-in ESS9281C Pro dac chip can handle high impedance headphones, although the output naturally reduces the higher the impedance (64 ohm: 33mW,  150 ohm: 21mW and 300 ohm: 12mW). The input power is also a factor, which means the S3 Pro performs better when connected to a computer than when connected to a smartphone. If you require a bit more power, the DH80S dac amp is twice more powerful than the S3 Pro and portable too, although not as compact. The S3 Pro audio port also supports microphone and playback controls so, you can use an earphone cable with inline microphone and remote.

The S3 Pro has 117dB signal to noise ratio (SNR), which is very high and a good thing when it comes to audio equipment. The SNR rating, basically, tells you how much noise the internal components make during operation. The higher the SNR rating, the better as it means less noise will be transmitted into the audio. As far as channel separation, the S3 Pro has 70dB. This is enough separation to prevent the left and right channel signals from overlapping, causing crosstalk. Technically, the higher the channel separation, the better although 70dB provides plenty of channel separation to experience a wide soundstage with the S3 Pro. You can get monoblock amps with near infinite channel separation, although turntable cartridges used for LP records perform just as good with just 30dB channel separation.

The S3 Pro USB-C connector measures 2cm long and, it's also made of aluminium alloy. The short cable has thick strain reliefs at the joints and, it's made with mix wiring, using individually insulated high purity silver wires and oxygen-free-copper (OFC) wires, which gives the cable a steampunk copper look. Speaking of sound, the S3 Pro 3 sound signature can be tuned via a firmware update. There are three tuning styles to choose from (treble, bass or balance), which makes the sound more treble focus or bass focus. The default sound is balanced. 

The S3 Pro dac amp has a small status led in the middle of the front panel, which is designed to indicate the current sampling rate. Tidal Masters sample rate is 96 kHz/24 bit, whereas DSD64 files have a sample rate of 88.2kHz/24 bit. DSD128 (a.k.a. Double DSD) has a sample rate of 176.2kHz/24 bit. The S3 Pro led indicator will light different colors: Red: 44.1k-48k, Blue: 88.2k-384k and Pink: MQA.

The Hidizs S3 Pro built-in ESS9281C Pro dac chip can decode MQA x8 unfolding, PCM audio up to 384 kHz/32-bit and DSD128 files natively. Because the ESS9281C Pro dac chip supports MQA x8 unfolding, it can fully decode MQA files, revealing the full resolution of the song, which means you can stream hi-resolution music via the Tidal app and Hiby Music player. The Hidizs S3 Pro supports Tidal master-quality audio recordings so, if you already have a Tidal HiFi subscription, you have full access to Tidal Masters songs. If you currently have a Tidal Premium subscription, you will need to upgrade.

The S3 Pro works with Windows computers (Windows 10 PC only), as well as MacOS, Android OS, iPad OS and iOS so, you can use the Hidizs S3 Pro with Android phones, Mac computers, Apple tablets and iPhones. That said, in order to use the S3 Pro with phones, they have to support USB OTG (Android) or USB accessories (iOS/iPadOS). As long as your Android device supports OTG function and has a USB-C port, you can simply plug the S3 Pro in to it, and you're good to go. 

For iPads and iPhones, you may need a USB-C to lightning cable adapter, depending on whether your iPad or iPhone has a lightning port. All current iPhones use Apple's lightning connection standard, while some iPad models use a USB-C port, including iPad Pro 11-inch (1st generation), iPad Pro 12.9-inch (3rd generation) and iPad Air (4th generation). There were hopes for a USB-C iPhone to be released this year but it seems Apple has abandoned the idea for the time being. 

The Hidizs S3 Pro dac amp ships with a Hidizs-branded protective storage case made of plastic. The storage case has a thick preformed foam insert with a cutout that snugly fits the S3 Pro and included dongle adapter (USB-C female  to USB-A male). You can buy the S3 Pro dac amp from Hidizs. Check out the review of the Hidizs AP80 dap music player and the Hidizs MS2 iem.