Questyle Sigma - Elevation Without Coloration

 4.5⭐️

 

+ Neutral and transparent sound signature 

+ Cleans and tightens the bass response 

+ Sizable boost in technical performance, particularly in separation, treble extension, and detail retrieval

+ Premium design that offers a great view of the circuitry within

+ Immaculate build quality

+ Stable Bluetooth connection and lossless sound quality 

+ Low/high gain switch

+ Headphone and IEM modes

+ Seperate data and charging ports

+ Pitch black background

+ Powerful

- Neutral signature may be a little boring for some

- Bass response is more refined but lacks fullness

- Indicator lights make it difficult to know the exact volume level and battery percentage

- No digital filters, EQ, app support, or pause/play/next track functions

- Glass body prone to scratches and fingerprints

- Can get quite hot

- No case included, though one is available for purchase separately

- Price may be a limiting factor

thaslaya's star rating system:

☆☆☆☆☆ - Fantastic!

☆☆☆☆ - Recommended

☆☆☆ - There are buyers but not for me

☆☆ - Can't see the appeal

☆ - Product is a failure

Disclaimer: 

This product was sent to me by Questyle in exchange for my honest and impartial review. I receive no compensation and all thoughts and opinions are my own.

Non-affiliated link for those interested:

https://questyleshop.com/products/questyle-sigma-bluetooth-headphone-amplifier

Gear used: 

● Samsung Galaxy S25 Ultra

● HiBy R3 II

● Various IEMs

Source:

● Listening was done using Amazon Music HD/Ultra HD and local FLAC files. 

Introduction:

Since their establishment in 2012, Questyle has obtained over 50 patents and won more than 40 international awards. Their mission is to help music lovers solve technical problems and break free from restrictive environments, offering an immersive audio experience. They are well known for both their desktop and portable offerings, including the CMA15, CMA18, and the M15 series. I recently tried my first Questyle product when I reviewed the M18i portable DAC/amp. I found the sound quality to be excellent, though the low battery life was a big letdown. This time around, we'll be taking a look at the new Sigma portable DAC/amp. According to Questyle, the name Sigma was chosen because it represents summation in mathematics, and this new DAC/amp embodies the culmination of their knowledge and innovations. The Sigma is currently available for $599 on Questyle's site as well as through other retailers worldwide. Let's break down this latest portable offering from Questyle and see how it performs.

Unboxing and build quality:

The design and detail of the packaging are great and the unboxing experience is quite nice. Upon opening the box, the Sigma sits in its own perfectly shaped indentation, and labels on the packaging highlight the buttons and key features of the device. If there's one thing I associate with Questyle products, it's their high-end design and great build quality, and the Sigma truly overdelivers on both. The overall size is on the larger side, similar to that of a small cellphone but a little thinner. It's definitely portable, but not as easily pocketable as something like a small dongle DAC/amp. The body is made of CNC-machined aerospace aluminum, and the front and back are covered in optical-grade transparent glass. The Sigma feels very premium in hand, and the weight balance is finely tuned—not too heavy or too light. Honestly, I just enjoy holding it and staring at all the beautiful exposed circuitry. While the design is very classy and the build quality is truly immaculate, I do worry about the long-term wear and tear of the glass surface, as it's prone to smudges, and scratches are sure to build up over time. I really think Questyle should be including a case at this price, but at least there's one available for neat freaks like myself. What does come included is a short USB-C to USB-C data cable, a longer USB-C cable for charging, a USB-C to USB-A adapter, and a manual. The Sigma is equipped with an AKM AK4493 DAC chip and Qualcomm's high-performance Bluetooth 5.4 chip for wireless connectivity. It features both 3.5mm and 4.4mm outputs, and separate USB-C ports for data and charging on the bottom of the unit. On the left side are four buttons and three switches. These buttons include power on/off, volume up/down, and a multifunction button to toggle between USB and BT connections. The switches are for low/high gain, headphone/IEM modes, and a hold switch to disable the buttons. The Sigma lacks a screen and instead opts to use LED indicator lights to display various information. There are lights for the BT and USB modes, gain level, data, IEM mode, and volume level, all of which I will go over in more detail below. Overall, the Sigma has a truly impressive build quality and a stunning design, but the lack of a case is worrisome, and I also think Questyle missed a great opportunity to make the Sigma MagSafe compatible for better transportability.

Technical specifications and features:

• AK4493 DAC chip

• Upto PCM 768Khz and DSD512 Playback

• 3.5mm SE and 4.4mm BAL output

• Manual Gain Option

• 64-Step Volume Control 

• Peak output Voltage :20vp-p

• Headphone Max. Output Power: >1200mW @32ohms balanced

• THD : as low as 0.0002%

• Noise Floor : -130dB

• Supports Bluetooth 5.4

• Compatibility with HArmonyOS, Android, Windows, MACos, IOS

• Apple MFI Certification

• Sony LDAC and Qualcomm APTX support

• Dual USB TypeC port

• 4300mah Battery

• 3.5 Hours Charging Time

Let's talk about functionality. The Sigma supports dedicated headphone and IEM modes, but to my knowledge, these only alter the delivery of power to the transducer, not the actual sound signature. In IEM mode, the signal path is minimized, which ensures an optimal listening experience with sensitive IEMs. It basically reduces the noise floor to ensure a pitch black background. Headphone mode is more powerful, making it easier to drive high-impedance transducers and reach higher volume levels. Speaking of power, the Sigma delivers up to 1200mW through the balanced output and drove everything I threw at it with ease. What's lacking in the feature department are any digital filter options, EQ, or app support. I, for one, am a big fan of variety, and the more options I have to fine-tune the sound, the better, so the Sigma does disappoint a little in that aspect. The indicator lights are pretty self-explanatory but worth talking about briefly. The Bluetooth and USB lights show which connection type is currently in use. The gain has two lights: red for high and amber for low. The data also has two lights, which illuminate only when music is playing: red for high-res, and amber for normal. The IEM light illuminates when that mode is enabled and turns off in headphone mode. There are also four lights underneath this row that denote the 64-step volume level. They are labeled 25%, 50%, 75%, and 100% respectively, and the lights get incrementally brighter or dimmer with each step. These same lights are also used to display the battery level, which can be shown with a quick press of the power button. I generally like the look and simplicity of the indicator lights, but they make it difficult to discern the exact volume and battery level. This is where a digital screen showing precise levels has the advantage, but then you couldn't see as much of that beautiful circuitry. There are also other lights to indicate which output is being used. Two red lights in the middle of the device will illuminate when using the 3.5 output and four for 4.4. As for Bluetooth performance, the Sigma connects quickly when powered on, and the connection is stable up to about 100 ft with an unbroken line of sight. It didn't perform as well through walls, obviously, but it works just fine for me when walking around the house. The thing that really bothered me, though, is when I ventured too far from the source and the connection became spotty, music would constantly stutter until I was right back next to the source. Because the Sigma doesn't include any pause/play functionality, there's essentially no way to fix the issue without actually interacting with the source. Another minor concern is that the unit can get quite hot, mostly when utilizing Bluetooth mode and using the 4.4 output, but it's worth noting. There's also no way to disable or turn off the indicator lights, which may be slightly annoying for some, but it honestly doesn't bother me. Overall, the Sigma has a decent amount of functions to offer, including the aforementioned headphone and IEM modes and Bluetooth connectivity, but I really wish there were some digital filters to fine-tune the sound, a companion app for EQ, or even simply more accurate battery and volume displays.

Battery performance:

The Sigma has its own battery and won't draw any power from the connected phone or DAP, so there's no need to perform my usual litany of source drain tests. The good thing is there are dedicated USB-C ports for data and charging, which enables the device to be charged while in use. Questyle boasts that the battery can last up to 12 hours on a full charge. Obviously, it ultimately depends on certain factors like gain level, wired versus Bluetooth connection, and headphone or IEM mode. In my testing, I was able to get just over 10 hours consistently on a full charge, mostly utilizing IEM mode with high gain and 4.4mm output. While less than the 12 hours claimed, that's still more than enough for me and I'm quite satisfied with the battery life. In Bluetooth mode, the battery does drain a little faster, but only marginally. At least the advertised 3.5 hours charge time from 0 to 100% is pretty accurate. Also, the Sigma will automatically shut off after about 10 minutes, which ensures the battery doesn't drain while not in use.

Comparisons:

● Questyle M18i ($350) - Here we have two Questyle devices with very different form factors and prices. The M18i is half the price of the Sigma and about a third the size. It has a similar quality build with a combination of metal and glass, but the design is much simpler than the transparent and more deluxe-feeling Sigma. The M18i also utilizes a screen instead of indicator lights, which displays more accurate battery and volume levels. Both units include 3.5 and 4.4 outputs, BT capabilities, separate data and charging ports, and low/high gain. The M18i offers PC and phone modes, which affect where the device draws its power, while the Sigma has IEM and headphone modes. Speaking of the battery, the Sigma lasts me about 10 hours, which is much better than the paltry 2 hours that the M18i has to offer. When it comes to sound, the Sigma is more neutral and sounds quite natural, whereas the M18i is a bit more W-shaped in comparison, putting a slight emphasis on the mid-bass, upper mids, and treble. It also has a more energetic and dynamic presentation compared to the smoother, somewhat relaxed Sigma. The M18i has a more mid-bass-forward low-end response, and while it sounds great most of the time, it can be a little fat and bloomy with certain tracks. The Sigma, on the other hand, is slightly sub-bass focused with better extension, texture, and resolution, but the impact is lessened, so the bass does sound noticeably less full or robust compared to the M18i. One of the things that surprised me about this comparison is how each one handles the treble. The M18i is a little edgier and doesn't necessarily help with any harshness or piercing qualities inherent in an IEM's tuning. The Sigma, though, is great at taking the edge off certain notes without sacrificing clarity and definition, and it also sounds airier and better extended. The M18i has a fuller-sounding stage, but the Sigma's is more expansive in both width and depth. The Sigma is also a step up in detail retrieval, timbre, and separation, though the M18i has better dynamics and note weight. Overall, these two sound much more different than I initially thought they would. Owning both might be a viable option depending on the transducers and tunings you own, but the Sigma is undoubtedly the better of the two when it comes to a pure, unadulterated sound quality metric.

● MuseHiFi M5 Ultra ($300) - The Ultra has become one of my favorite and most used sources since I acquired it earlier this year (a little birthday present to myself), so it should make a good comparison to the Sigma to see how it stacks up against a more expensive product. Both of these devices have very nice build quality and are similar in weight, size, and overall design. The Sigma is a little taller and wider, but the Ultra is thicker. Both have a combination of glass and aluminum, but the window of the Sigma shows much more of the circuitry within, and it just has a more premium overall feel. The Sigma utilizes indicator lights for the battery level and various functions, while the Ultra has an actual screen, which I do prefer. Both include 3.5 and 4.4 outputs, BT capabilities, gain adjustment, and separate data and charging ports, but I will note that the Sigma has much better battery life. What sets these two apart is that the Sigma has a dedicated IEM mode for sensitive transducers, while the Ultra includes seven digital filter options (though to be fair, they all sound the same to me). Also, I would be remiss if I didn't mention that the Ultra comes stock with a nice leather case, whereas the Sigma does not. When it comes to the sound, I chose not to utilize the Ultra's tube mode, as it can color the sound quite a bit. With the Ultra set to transistor mode, these two sound more alike, but they still have differences. The Sigma has a neutral and balanced sound signature, and it does very well to preserve the innate tuning of the paired transducer compared to the Ultra, which adds a noticeable bass boost and has a slightly darker sound signature. The bass of the Ultra is a little exaggerated with more fullness, mid-bass impact and slam, an extra level of rumble, and slower decay. The Sigma's bass is better articulated and maybe a little more natural-sounding, but it also sounds a little bass-light, especially compared to the Ultra. The vocals are just a touch recessed on the Ultra, whereas the Sigma keeps them truer to the tuning. They are also better separated and more even-keeled, without any added inflection. The treble of the Ultra is a bit skewed towards a darker presentation, whereas the Sigma offers better extension, more air, and a higher level of resolution. The Ultra has a slightly deeper soundstage, while the Sigma's is wider. The Sigma also has better dynamics, detail retrieval, separation, and imaging, but the Ultra offers more note weight and a better level of layering and cohesion. Overall, the Ultra offers a bassier and more musical affair that pairs best with more technical-style tunings. The Sigma sounds much cleaner and better balanced, with a noticeable level of air that's missing on the Ultra. These two devices complement each other well, and both make a fine addition to any collection. 

● iFi GO blu ($200) - The size and build quality of these two devices are quite different, not to mention the price. The Sigma is much larger and heavier, but it also has much better build quality and a higher-quality design. The blu's smaller form factor makes it much easier to take on the go (hence the name), but the mostly plastic build feels a little cheap, especially compared to the aluminum and glass body of the Sigma. Function-wise, both sets have Bluetooth, but that's essentially where the similarities end. The blu includes iFi's XBass and XSpace, and it utilizes a scroll wheel for volume control, which also has a button for pause/play and next/previous track functionality. The Sigma has 64-step independent volume control, a low/high gain switch, headphone and IEM modes, and separate USB-C ports for data and charging. When it comes to the sound, the Sigma has a more neutral sound signature compared to the blu, which is somewhat V-shaped. Neither has an inherently energetic flavor, but the blu strikes my ear as the more engaging of the two. In the bass, the blu has an increased level of rumble and impact with a slower decay, but some notes can sound a little ill-defined and flabby. The Sigma is more resolving and has much better texture and a deeper-reaching sub-bass extension with a better sense of body in the low end. In the midrange, the blu recesses vocals just a bit, while the Sigma does a better job at preserving their natural position in the tuning while also keeping them separated from the bass response. The blu does add a touch of warmth, though, and both male and female vocals have more emotional weight, which I really enjoy. The treble responses are quite close, but the Sigma has better texture and definition, as well as a level of sparkle and crispness the blu simply doesn't possess. The Sigma has better technicalities across the board, most notably in soundstage and detail retrieval. It also offers better extension on both ends, which helps to convey a better sense of space and completeness, and vastly better wireless sound quality too. Ultimately, these two are quite different, and I'd recommend the blu to someone looking for a fun, portable DAC/amp with nice options like XBass/XSpace and a focus on musicality. The Sigma would be more for those seeking a very high-quality and powerful transportable source with great technical prowess and natural presentation.

● iFi hipdac 3 ($200) - From a build and design standpoint, these two devices are quite different. The Sigma has an ultra-premium design that utilizes a combination of glass and aluminum to create a very classy and eye-catching aesthetic. The hipdac's design is much more simplistic, but it does look like a little flask, which I always thought was cool. Also, the full aluminum body is undoubtedly more durable and less prone to scratches or cracks than the Sigma's glass. When it comes to features, the hipdac has iFi's XBass and IEMatch, a low/high gain button, and a volume wheel for fine-tuned adjustments. It's also the only DAC in this comparison section without wireless capabilities. The Sigma has 64-step volume control via the volume buttons, a low/high gain switch, IEM and headphone modes (which function similarly to IEMatch), indicator lights for battery and volume percentage, and of course, Bluetooth. Both devices actually feature separate USB-C ports for data and charging, which I appreciate. As far as the sound goes, the hipdac is somewhat V-shaped with a fuller sound, a slight bass emphasis, and a touch more lower treble energy. Due to its V-shaped nature, the midrange sounds a little recessed, especially compared to the Sigma, which has a more neutral sound signature. The Sigma also has noticeably better extension on both ends, especially when it comes to the treble air. The midrange sounds cleaner too, if not a little less emotive. Technically speaking, the Sigma has a much more expansive soundstage, smoother transients, better separation, and a higher level of detail and clarity. The hipdac offers a bit more note weight and a slightly more dynamism, which can be great with certain IEMs. Ultimately, these two are much more different than they are alike, and they actually complement each other quite well. The hipdac is a little more fun and engaging, and the added bass emphasis can be nice with certain tunings. However, the Sigma offers an impressive level of refinement and quality that is leagues above what the hipdac is capable of, though it can sound a touch boring at times. 

● iFi GO blu Air ($130) - The Air is nearly identical to the original GO blu, so I won't bother rehashing the things I touched on in that comparison, though I'll still highlight a few key differences. Firstly, the Air has an even cheaper build quality than the original blu, and its plastic body is quite a stark contrast to the glass and aluminum of the Sigma. Second, in an effort to minimize redundancy, I opted to utilize the Air's MIN filter option since it offers a slightly different sound signature from the STD filter, which sounds identical to the original GO blu. Lastly, since the Air is a wireless-only device and cannot be used wired directly to a source (though it can still be charged while in use), I performed this comparison using the Sigma's BT connection for a more apt comparison. When it comes to the sound, the Air is a bit V-shaped with more bass and upper mids/treble emphasis while the Sigma is more neutral. The Sigma has better sub-bass extension and a cleaner texture, but the Air offers a slightly fuller bass response with more rumble. In the midrange, the Sigma is tuned a little flatter and has a superior balance to my ear. The Air pushes female vocals a bit further forward and that accentuation continues into the lower treble too. The Sigma manages to smooth out any peaks or rough notes in the treble while also having better extension and air. The Air has a bit more excitement in the upper frequencies, but it also sounds a little thinner, with more incidence of harshness and sibilance depending on the paired transducer. When it comes to technical performance, the Sigma has better detail retrieval, separation, soundstage, and note weight, but the Air does have slightly better dynamics. Overall, I think these two actually make a pretty good pairing to have in a collection. Each delivers a unique sonic flavor that pairs best with certain tunings, and the much cheaper and more portable Air makes for a great on-the-go option, leaving the Sigma for home or office use. The Air also offers two distinct filter options that add a level of versatility, whereas the Sigma is more of a technical powerhouse that delivers top-notch performance.

Sound impressions:

Throughout my testing, the Sigma portrayed a few consistent themes: cleanliness, maturity, and technical elevation. It definitely has what I would call an "audiophile" style of sound signature, which is to say there's no coloration or added emphasis outside of what is innate to the tuning of the paired transducer. The bass response became a little tighter, better behaved, and more resolving. Unfortunately, the sub-bass loses a little rumble and weight compared to other devices I tested, but the Sigma still preserves mid-bass impact and fullness, which I appreciate. It essentially trims the fat of a flabby bass response, but in doing so, it can sometimes go a touch too far, causing the bass to lose a little character and uniqueness in the process. In the midrange, notes are better separated, and there's an added level of clarity for instruments and vocals alike. The Sigma won't add any smoothness or emotional emphasis, but neither does it sound too cold or sterile. The treble is actually my favorite part, as the upper frequencies sound a touch smoother with better air and extension. The best part is that it slightly dulls the edge of troublesome notes, making them much more agreeable. Honestly, this particular ability cannot be understated or overvalued for a treble-sensitive listener such as myself. Also, the Sigma has a way of elevating the entire technical performance. The stage becomes more expansive, small details and nuances are more easily discerned, and frequencies are better separated for less congestion and added clarity. While the Sigma may lack a sense of uniqueness or specialness of its own, it does well to highlight the special qualities of a particular IEM without imbuing any coloration of its own or altering what makes a particular IEM unique in the first place. The presentation might be a little drier than I prefer, and it could do with a touch more musicality, but there's absolutely no argument to be made when it comes to the sheer quality of sound the Sigma produces. Like most sources, this one won't offer a universally great pairing with everything you throw at it. For me, it pairs best with the AFUL Performer 5+2 and Punch Audio Martilo, but it didn't work as well with the Brain Dance. Also worth mentioning is that I experienced no hiss or noise in any modes and configurations I tested.

In conclusion:

The new Sigma from Questyle is a mightily impressive portable DAC/amp from a company known for its high-end gear. The exquisite design and build quality exude luxury. It has two separate modes and a low/high gain switch that ensures there's plenty of power to drive just about anything you have on hand. The battery life is great, the wireless sound quality is excellent, and Bluetooth version 5.4 ensures a stable connection with a decent range. While those are all nice features, what matters most is the sound. The real specialness of the Sigma comes from its superbly natural and overall neutral presentation. In fact, It has to be the most uncolored DAC I've heard to date. It never attempts to add any emphasis or coloration outside of what's inherent to the transducer it's paired with. It also has a way of elevating the tuning and technical performance to another level, which can be quite enlightening and addictive. But there's always another side to the coin. In this case the Sigma tends to sound a little dry and more relaxed in the bass than many other DAC/amps I compared it against. I wouldn't necessarily call it a fun or engaging source, but the sheer quality of the sound is nothing short of fantastic. Questyle also made some stylistic choices I may not love, such as using indicator lights instead of a screen. The fact that it doesn't come with a case to help protect the beautiful craftsmanship is a big oversight in my eyes. Also, a few more features like digital filters or app support to further customize the sound would be welcome. Still, I think Questyle should be very proud of what they've made, and the Sigma has become an indispensable piece of gear in my repertoire. This one should be a top consideration for anyone in the market for a high-performance portable DAC/amp.