Questyle Audio Engineering CMA600i headphone amp/preamp/DAC

Headphone amps and amp/DACs
Questyle Audio CMA600i
Questyle Audio Engineering CMA600i headphone amp/preamp/DAC

More than many manufacturers of high-end audio electronics, Questyle is an engineering-driven firm led by the talented audio technologist Wang Fengshuo (whose anglicised name is Jason Wang). Thus far, Mr Wang’s greatest single contribution to music arguably involves his evolutionary development and refinement of ‘Current Mode Amplification’ (as opposed to the far more commonly seen voltage mode amplification)—a circuit topology that Questyle applies in personal audio devices and other audio components both large and small. Two good examples would be the firm’s excellent QP1r digital audio player reviewed in HiFi+ issue 129 and the spectacular, award-winning, four-chassis Gold Series reference stack, reviewed in Hi-Fi+ issue 137.

Many consider Questyle’s ‘Golden Stack’ to be the finest all-around headphone amp/DAC system on the planet, which comes as no surprise in light of its somewhat stratospheric £10,096 price tag. But if the Golden Stack offers ‘ceilings unlimited’ performance at a cost-no-object price it also forces us to ask what high performance alternatives are available to serious music lovers who are constrained by relatively ‘earth-bound’ budgets? Happily, Questyle has an answer in the form of its new CMA600i headphone amp/preamp/DAC, which sells for the reasonable sum of £1,199.

Given the huge price disparity between the Golden Stack and the CMA600i, you might assume the junior model had to drop features or cut corners in order to achieve its more manageable price, but that isn’t the case at all.

First, the CMA600i incorporates a full-featured DAC section based on the excellent 32-bit AKM AK4490 DAC chipset supported by what Questyle terms “a unique 3X clock structure” plus a “newly developed switch capacitor filter ‘OSR Doubler’ that greatly reduces sound degradation from noise shaping, achieving a flat noise floor up to 200kHz.” Questyle further claims that the AKM DAC helps reduce jitter and pre-ringing “to undetectable levels.” In keeping with past Questyle design practice, the CMA600i DAC section not only handles PCM files at resolutions up to 32/384, but also can play DSD64/128/256 files via so-called ‘True DSD’ decoding, meaning the Questyle does not require DoP (DSD over PCM) processing, but rather “accepts the DSD bit-stream directly from your computer.” The DAC provides an optical S/PDIF input, a coaxial S/PDIF input and output, and a USB Type B input.

Second, the CMA600i headphone amplifier section uses Questyle’s patented full balanced, Class A Current Mode Amplification circuit, as patterned after the amplifier section of the firm’s flagship CMA800R headphone amplifier (reviewed in Hi-Fi+ issue 133). The CMA600i headphone amp produces remarkably low distortion figures (<0.00034% distortion) while also offering a generous amount of power (220mW @ 300 ohms or 950mW @ 32 ohms in single-ended mode and twice that or more in balanced mode). The headphone amp provides dual single-ended outputs (via two 6.35mm headphone jacks) and a balanced output (via a 4-pin XLR jack).

Finally, in a rarely seen design touch, the CMA600i incorporates two separate and independent amplifier sections—one designed to power your headphones and the other optimised as a preamplifier circuit to drive power amplifiers or self-powered loudspeakers. Like the headphone amp, the preamp also sports both single-ended outputs (via stereo RCA jacks) and balanced outputs (via stereo 3-pin XLR jacks). Both the preamp and headphone amp share common inputs, including a stereo analogue input, plus the aforementioned combination of S/PDIF and USB digital inputs.

Completing the picture is Questyle’s traditionally very high quality of build, featuring precision CNC-machined chassis panels including 10mm thick aluminium top and bottom chassis plates, with assembly techniques said to yield, “stable heat (dissipation characteristics), excellent control of sympathetic vibration, and excellent shielding from RFI/EMI radiation.” Significantly, Questyle has the chassis of the CMA600i made by Foxconn, the Chinese precision manufacturing house perhaps best known for constructing Apple’s vaunted iPhones. Extremely high-quality parts, such as Nichicon FG and WIMA capacitors, DALE resistors, an ALPS motorised potentiometer, and a Plitron toroidal transformer are found within. Last but not least, the unit ships with a remote control that provides volume up/down, mute, and digital filter switching functions for the CMA600i (the same remote can also control several other Questyle products).

The question many will ask now is just how close the CMA600i is able to come to the sound quality of the Questyle’s upper end models. In fact, the CMA600i does an almost shockingly good job of channelling many of the defining sonic characteristics and much of the sonic performance of the Golden Stack in a very compelling way.

All the expected Questyle sonic virtues are present and accounted for in the CMA600i. There is the firm’s even-handed tonal balance, effortless speed and definition, very high levels of transparency and detail, and above all a quality of ample but always agile power on tap (subjectively speaking, there’s more power on hand than the unit’s output specifications would seem to promise). The result is an amp/DAC that has an uncanny knack for elevating the performance of most any headphone you might care to try.

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