Shenzhen, China-based audio equipment maker Questyle will release the MEX, a dongle-type portable DAC/headphone amplifier, in mid-December. The expected price is around ¥33,000 (approximately $210). The company announced the product at a launch event held in Tokyo on November 7. Pre-orders have been open since the same day on the crowdfunding site Mimigoto, with plans starting at ¥26,400 (approximately $170), a discount of up to 20%. Orders will be accepted through November 29.
The MEX carries two ESS DAC chips, the ES9219Q, and four “SiP current-mode amplifier modules” — Questyle’s patented current-mode amplification circuit packaged as a system-in-package (SiP). It supports native playback of PCM up to 384kHz/32bit and DSD up to 256. The housing is bus-powered, connecting directly to a smartphone or PC, and contains no built-in battery.
The output terminals consist of one 4.4mm balanced and one 3.5mm single-ended connection. Maximum output is 4V for balanced and 2V for single-ended (both at 300Ω). Gain can be set to three levels — high, medium, and low — and volume adjusts across 64 steps. The 3.5mm jack also supports earphones with a microphone, and the unit itself has a built-in microphone.
Its biggest feature is two modes that let users switch how sound is shaped. A slide switch on the unit toggles between “PURE mode,” which minimizes signal processing to amplify the original sound, and “TUNE mode,” which allows fine-tuning of sound quality from a smartphone app. The app supports both iOS and Android and has obtained Apple’s “MFi certification.” When connected to an iPhone, the app launches automatically.
TUNE mode offers a 10-band parametric EQ (PEQ). Frequency, gain, and Q value can be set for each band, and the filter type can be selected from five options: low shelf, peaking, high shelf, low-pass, and high-pass. Adjustments can be made while visually checking the results on a graph, and created settings can be saved and recalled at any time. It also features “DRE (Dynamic Range Enhancement),” which picks up minute sonic details to expand the usable dynamic range, plus two types of DAC digital filters; these work in both PURE and TUNE modes.
Founder and CEO Wang Fengshuo traveled to Japan to speak at the launch event. According to Wang, the idea for current-mode amplification dates back to 2004, when he was a student at China’s Yangzhou University and accidentally assembled a circuit during a communications circuit experiment that showed excellent characteristics for audio use. After graduating, he first joined a U.S. IC design company, worked on solving issues for mass production, and then founded Questyle in Shenzhen in 2012.
Whereas ordinary amplifiers amplify music signals in voltage form, current-mode amplification first converts the signal to current, amplifies it, and finally converts it back to voltage. The advantages are said to be that distortion is unlikely even with large signals, and current consumption can be kept low while maintaining a wide bandwidth. Initially, the effort required to match transistor characteristics was a barrier to mass production, but after repeated improvements the circuit has now been miniaturized to a 3mm-square IC chip size.
Asked why the device adopts a skeleton structure that exposes the board circuitry on the back, Wang said, “Our stance is to show what’s inside for things we’re confident about.” He also indicated plans to build out “Q-Code,” a mechanism allowing users to share sound-quality settings with one another, and to spread the company’s “easy Hi-Fi” concept of letting people enjoy Hi-Fi regardless of whether they have specialized knowledge.
At the event, audio critic Kenji Nomura and audio/DTM writer Ken Fujimoto explained how to use the sound-tuning features. Nomura noted that conventional dongle-type DACs draw power from the smartphone, making it hard to raise the signal-to-noise ratio, and said the MEX achieves effective noise reduction despite having no battery, and that with its low distortion, PURE mode earns high marks. Fujimoto recommended using the PEQ not to dramatically change the sound but to pinpoint-adjust frequency bands of concern.
Key specifications are as follows.
| Item | Specification |
|---|---|
| DAC chip | ESS “ES9219Q” ×2 |
| Amplifier | SiP current-mode amplifier module ×4 |
| Supported formats | PCM 384kHz/32bit, DSD256 |
| Output terminals | 4.4mm balanced / 3.5mm single-ended |
| Maximum output | 4V (balanced), 2V (single-ended, at 300Ω) |
| Gain | 3 levels (H/M/L) |
| Volume adjustment | 64 steps |
| Power | Bus-powered (no built-in battery) |
| Expected price | Around ¥33,000 (approximately $210) |
| Pre-order | From ¥26,400 (approximately $170) (through November 29) |
Note: Prices include tax. Pre-orders are being accepted on the crowdfunding site Mimigoto.
The portable DAC market into which the MEX is being launched has expanded mainly among people who enjoy high-quality earphones with their smartphones. However, prices range widely from a few thousand yen to tens of thousands of yen, and major smartphone makers and Chinese players are entering one after another. Questyle positions its in-house-developed amplifier circuit and rich adjustment features as its differentiation axes. The ¥30,000-plus price places it in the mid-range for dongle types, aiming to capture not only users accustomed to sound tuning but also those who want to correct the quirks of their earphones.
For the company, the MEX is a product that extends the current-mode technology cultivated in desktop and portable players into a more accessible price range. Along with expanding brand recognition, how firmly it can establish the ongoing touchpoint of sharing settings via the app will likely shape future sales.