Astell & Kern PEE51 USB-C Dual DAC Cable Review – Je Ne Sais Quoi

Sound –

Preamble

I actually am not a huge fan of doing dongle reviews, many use the same componentry and measure well. As such, there’s not a whole lot of utility comparing between them as most provide similar performance. The Dual DAC is a little different, of course the Astell & Kern name piqued my interest, but we do observe some changes too such as the independent amplifier and more unconventional Cirrus Logic DAC chip – in addition to the dual mono setup. This represents an interesting direction for the form factor. That said, it remains a highly competitive market and the 2-ohm output impedance especially is a potentially limiting factor that I will test in-depth below.

Frequency Response –

Testing Methodology: RMAA via Startech External Sound Card

The A&K Dual DAC Cable has a linear frequency response suggesting that it represents audio with great fidelity. Due to the quality of my sound card, I am unable to reliably test other measures such as distortion and crosstalk so they will be used as a personal reference only. Qualities here can also impact the sound as I will detail via subjective listening.

Output Impedance & Hiss –

Testing Methodology: SPL volume matched comparison through an inline splitter to THX789 + SMSL SU9 to Campfire Audio Andromeda

A&K quote a 2-ohm output impedance on their website which shouldn’t pose a problem for most listeners but is not ideal for especially low-impedance in-ears. For reference, general consensus dictates that the ideal output impedance is 1/8th of the attached gear so for sub 16-ohm multi-driver IEMs some colouration may be evident. For the vast majority of gear I tested the dongle with, it delivered a sound similar to my THX789 with 1-ohm output impedance.

However, to assess its effect on low-impedance monitors under that 16-ohm value, I tested the dongle with Campfire Audio’s Andromeda, renowned as one of the most source sensitive in-ears on the market. The dongle provided a noticeably brighter sound that was more treble-forward and bass became diminished and slightly rolled-off. It remained listenable but clearly coloured relative to the intention of the company.  

On the flipside, the noise floor is low with hiss being barely audible on the lowest setting on my most sensitive in-ears and essentially inaudible with music playing. This makes the Dual DAC Cable a good choice for low volume listeners who will benefit from minimal added noise even on the most sensitive gear. So long as your multi-driver IEMs have an impedance over 16ohms or a flat impedance design, you will benefit from minimal colouration due to the output impedance. Single-driver models should not be affected and it does contribute to a slightly lower noise floor than most dongles whilst retaining admirable driving power. If you do have a collection of low-impedance multi-driver IEMs, there is no shortage of alternatives with a 1-ohm or sub 1-ohm rating.

Subjective –

Testing Methodology: SPL volume matched comparison through an inline splitter to THX789 + SMSL SU9 to Custom Art Fibae 7 (flat impedance). Powered by Xperia 5 II with Poweramp Pro via high-resolution output.

The Dual DAC Cable is immediately a smooth and clean sounding source. It impresses with its composure and separation in addition to offering a good amount of depth and space for such a compact source. It has a light warmth in the low-end in addition to an uptick of bite in the lower-treble that redeems some detail presence and engagement. The midrange is coherent and slightly lush but with good definition and extension. Overall, it represents a refined and natural sound with a lack of any harshness or fatiguing properties and an emphasis on a linear, detailed treble.

Bass –

Compared to a good desktop source or even a higher powered portable one, the Dual DAC doesn’t have quite the same extension. It has less authority in its sub-bass kick, preferring a slightly rounder and smoother note presentation. To compensate, there’s a light rise in the mid-bass, instigating its light warm tone alongside a fuller bass note presentation. It isn’t muddy nor bloated, but certainly slightly richer than neutral. Besides this, the Dual DAC showcases a controlled and nicely detail presentation.

Attack is moderate while note decay is a touch slower, another prime source of its smoothness. Despite this, separation is not lacking, mid-bass retains admirable definition and complex passages are flattered with good organisation and timing. Astell & Kern have achieved a good balance here between qualities, achieving a smooth and organic low-end presentation if not the most dynamic and impactful one. I will reiterate that the changes are not overt, only apparent to me in volume matched AB testing.

Mids –

Given the lesser extent of the low-end colouration, the midrange showcases a mostly linear and natural expression. Light warmth is apparent alongside the smallest uptick in note body. However, for the most part, positioning and timbre are accurate and even throughout. Vocals are flattered with a slight lushness that makes the Dual DAC a pleasure for easy and longer listening sessions. There appears to be slightly enhanced contrast between the bass and midrange, redeeming some separation and enabling good amounts of definition despite the DAC’s generally smoother character.

It is not exaggerated so the DAC still retains a modest focus on coherence over contrast overall. It is also moderately articulate which aids definition on top without introducing any sharpness or sibilance. Instruments and vocals appear well-balanced and the DAC is able to render distance and depth especially well when considering its form factor due to its even-handed midrange presentation. Though not perfectly neutral, I do appreciate the refinement that the slight uptick of coherence here brings, it is a very well-natured and natural sound that is tastefully and subtly coloured so as not to affect separation or definition.

Highs –

The Dual DAC provides a mostly linear and even-handed top-end presentation with just a hint of additional bite in the lower-treble. Instrument positioning remains accurate, though there’s impressively strong fine detail retrieval in the foreground as a result with great separation. Instruments are flattered with an accurate timbre and a nice, natural decay. The Dual DAC lacks any iota of thinness here, delivering accurate body and a highly textured note presentation.

This is most evident with high-hats and cymbals, where there is a good balance between attack and decay enabling natural, fully-fleshed out notes. The hint of added sharpness in the note attack gives the source a bit more energy, which admirably counterbalances its smoothness elsewhere. Besides this, the Dual DAC provides impressive headroom and space alongside good resolution. It extends well into the top-octave, delivering an ear-pleasing sparkle and background details are well-resolved too. The Dual DAC is a great performer here though difficult to quantify on a spec sheet, I found myself greatly enjoying its balance of refinement and strong detail retrieval.  

Soundstage –

Of course, I didn’t expect the Dual DAC to rival my desktop stack in terms of expansion but it does get impressively close for such a compact source. The Dual DAC has great width and well-balanced depth too. This makes it more immersive than most dongle-style sources which usually sound more one-dimensional to me. Though its imaging cannot compare to a larger source, it is accurate with clearly a distinguished foreground and background. There is even some coronal projection though nothing holographic or especially multi-dimensional. Nonetheless, it is a nice, spacious presentation with simply good positioning and organisation. Separation is not the best in-class due to its warmer and lusher low-end though isn’t lacking either, especially given its above average space.  

Driving Power –

Lime Ears Pneuma: ThePneuma is an efficient multi-driver hybrid and I found it to be essentially source agnostic. The bass was almost identical to my desktop stack, deep reaching and dynamic with great control. The presentation as well was very similar. The midrange surprisingly differed, being thinner on the desktop source and smoother and more refined on the Dual DAC. Treble was slightly brighter on the Dual DAC but not by much. The soundstage was almost as wide as the desktop source but not quite there and the imaging was sharp if not quite as multi-dimensional. I enjoyed this pairing a lot, especially the smoother midrange and there was zero background hiss.

Final E5000 (93dB, 14ohm): I find the E5000 to be one of the most difficult to drive in-ears requiring a good level of power to achieve a controlled note presentation. My desktop stack immediately provided a bit more extension and physicality in the sub-bass contributing to a slightly bolder and richer voicing. Despite this, the Dual DAC sounded equally controlled and defined through the mid-bass, being a touch cleaner. The midrange was even and natural on both as was the treble. The soundstage was narrower on the Dual DAC but had almost as much depth, contributing to a well-rounded soundstage. There was zero background hiss on this pairing.

Audeze LCD-X (103dB, 22ohm): The LCD-X is a reasonably sensitive full-size planar but also one that scales well with more resolving sources.  In terms of volume, around 50% was sufficient, leaving plenty of headroom for higher volume listeners. Bass was just a touch diminished relative to my desktop stack but was surprisingly even and deep reaching. Sub-bass definitely had a bit more kick on my THX amp that said. The midrange was quite even with just a bit more depth on the desktop stack, partially due to its more robust bass. The high-end remained balanced and well-textured. Similarly, the soundstage was impressive spacious, of course, not to the same extent. The Dual DAC kept up well here, I was impressed.

Suggested Pair-ups

TheDualDAC I would characterise as a slightly smoother and less impactful source, therefore, suiting more aggressive sounding gear best. This includes something like the Pneuma with its sub-bass boost and clear upper-midrange where the Dual DAC serves to refine its sound. Nonetheless, even for a darker headphone like the LCD-X, the Dual DAC wasn’t veiled or over-warm. It has versatile synergy due to its linear top-end and since it avoids overly enhancing the sub-bass region, it can get away with a bit more mid-bass. On all pairings, minimal hiss was enjoyed, and power output was sufficient for IEMs, even the less sensitive E5000 and portable headphones will be fine. For full-size headphones, a slightly more powerful source would best suit for a more dynamic experience but there is ample power to retain a balanced if not ideal sound at the very least.  

Next Page: Comparisons & Verdict

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ABOUT AUTHOR

Ryan Soo

Ryan Soo

Avid writer, passionate photographer and sleep-deprived medical student, Ryan has an ongoing desire to bring quality products to the regular reader.

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