Questyle has proven to be one of the unsung heroes of the next generation of Chinese high-end audio manufacturers and a brand that many in the Head-Fi community hold in high regard. They have not been an overnight success and the company which builds each component by hand in a very impressive facility in Shenzen has never been known to skimp on quality. The Questyle CMA Fifteen DAC/Headphone Amplifier is their new flagship and our focus this week.
The DAC/Headphone Amplifier category is starting to get a lot more attention outside of the Head-Fi community because so many people transitioned to working from home during the pandemic and are sticking with a remote or hybrid situation; a lot of people listen to music while they work and with nobody in the next cubicle to complain about their choice of music or volume level — this type of product makes a lot of sense.
The Questyle CMA Fifteen couples a current-mode DAC (most are) directly to a current mode amplifier (most are not) and bypasses the typical I/V stage seen in many other designs in the process.
Why would Questyle do this?
Their explanation is that this creates a “simpler, purer sounding device,” but what does that really mean for consumers?
Follow the Science
There are two common types of amplifiers used in audio; voltage amplifiers and current amplifiers and often they are used together inside a larger product like a receiver or integrated amplifier.
They can be thought of like this. When a signal is received from a microphone or source device, it is generally a very small signal both in voltage and current.
Voltage amplifiers take that small input signal and raise the voltage so now we have a bigger signal but it is still a very low power signal as a voltage amplifier does nothing to increase power.
The next step in the path is usually a current amplifier that takes that larger low power signal and adds additional power to better drive woofers. Voltage is great for carrying a signal, but current is needed to make moving parts operate.
When it comes to loudspeakers, we probably need both voltage and current amplifiers somewhere along the path, but for headphones with much smaller drivers, we can often get away with just one or the other.
If we have a large voltage swing and a small amount of power, we can make a headphone respond quite nicely in most cases so a single voltage amplifier is often all that is needed between that low-power signal and the headphone.
Likewise, a single current amplifier can be used between the source and headphone and output a signal that while still small — is much more potent and have a similar result.
Voltage mode amplifiers are simpler to build and less expensive due to lower power supply costs. After all, a pure voltage amplifier only needs enough power to run the electronics as none is being fed into the signal.
This makes voltage amplifiers the choice of most headphone amp manufacturers.
Voltage mode amplification, however, has some issues as well. Anytime a signal is being changed, we run the risk introducing artifacts and most voltage amplifiers are not true amplifiers in the sense that what is passed to the output is a copy of the original signal at a higher voltage and not the original signal itself.
So the act of copying that signal into a larger version of itself may have flaws or artifacts that are audible. Think about using an overhead projector to display an image. What is seen on screen is often a lower resolution and larger version of what can be seen looking directly at the original transparency.
Current amplification can be thought of as taking that small input signal and telling the system to use the signal as it exists, but playing it with more authority. This can only be used in systems where the signal is large enough to be used directly by the output since we are not increasing the signal size and again a perfect fit for small transducers like headphones.
In current amplification, the original voltage is passed without change instead of getting a copy of the original signal as seen in voltage amplification. This eliminates a potential source of error and noise. The downside is that current amplifiers require larger, more potent power supplies and consume more power than their voltage designed counterparts.
Still with me? Sorry the long technical rant.
A Path Forward
Questyle choses to use current amplification for its headphone products as it eliminates the typical shortcomings of the voltage amplification model and allows the original signal to travel from the output of the DAC to the transducer unchanged.
The Questyle CMA Fifteen celebrates both the 15th anniversary of the company and all of the progress they have made with Current Mode Amplification since their inception.
It is also one of their most ambitious products yet — EIC Ian White reminded me of his experience many years ago at CES listening to a pair of their prototype power amplifiers driving a pair of Focal Utopia Loudspeakers to ridiculous levels that made many scamper from the room; they were also products that possessed incredibly high levels of resolution and control.
Definitely Not a Little Box Made of Ticky Tacky
The CMA Fifteen are made out of heavy gauge (10mm) anodized 6063 Aluminum alloy with a rather striking matte black finish. This is much heavier than most pieces of audio gear and is done to help reduce resonance and stabilize the ground.
One feature I really appreciate, are the feet which are larger and more functional than the far too common bumps in the aluminum shell that others have started using to cut costs.
The feet on the CMA Fifteen allow for proper airflow beneath the unit.
One odd quirk that some people may not like or understand was the decision to put gain controls on the underside of the chassis; a practice that has become quite common with phono preamplifiers from brands like iFi Audio and Simaudio.
To adjust the gain, the unit should first be powered off and unplugged, then all four switches should be moved to the opposite position. Since the CMA Fifteen uses differential amplification, there are four distinct amplifiers in the unit and the gain has to be changed on all at the same time to avoid channel imbalances.
The front panel of the Questyle CMA Fifteen is quite busy but also very easy to use; the power switch occupies a spot on the far left of the panel, followed by a bank of LEDs that are used to indicate the input source, and bit depth/rate. The rest of the real estate is occupied by a “source” button selector, a pair of toggle switches for DAC/Amp function and Bias Control, 3 output jacks, and the very well made volume control knob.
Questyle has been involved in the high-end headphone space for a long time and know that their customer base is going to demand a 4.4mm balanced output, 6.35mm single-ended output, and 4-pin XLR balanced outputs or raise a major stink.
The rear panel of the unit has USB Type-B and Type-C inputs along with optical and coaxial inputs on the far left, followed by a pair of RCA inputs.
The decision to include the single-ended RCA inputs adds another layer to this and one that adds additional value to the CMA Fifteen — it’s viability as a DAC/Preamplifier for use with a power amplifier or active loudspeakers.
If you own an external phono preamp and you want to listen to vinyl over your headphones while you work — the CMA Fifteen makes that an easy thing to accomplish.
Questyle have also provided a pair of single-ended RCA and a pair of 3-pin XLR outputs as well. The outputs have 2 switches that allow for Standard (14dBu) or Studio (20dBu) output and fixed or variable controlled output; dBu measures decibels relative to 0. 775 volts with an open or unloaded circuit.
While 0.775V may seem arbitrary at first glance, it is the voltage that delivers 1mW into a 600 ohms load. Home stereo equipment generally expects the standard setting while professional audio gear will often need the higher setting to perform at optimal levels.
There is also a Bluetooth antenna, pairing switch, 110/240V switch, and power jack.
Input options are broad but which one you decide to use will depend somewhat on the file or audio format being used. Apple Lossless is supported via the USB Type-C port, while MQA and DSD are supported over USB, and optical and coaxial are limited to 24-bit/192kHz PCM which covers 99% of digital music currently available.
It takes all types sometimes to really moan and complain about nothing.
Another interesting quirk that users should know about is the use of USB Type-B versus USB Type-C when both ports are connected to devices; the USB Type-C port is given priority because “it has lower latency and less wire loss” according to Questyle when I asked them about it.
The Bluetooth input offers SBC, AAC, and LDAC support but does not have aptX support as of right now.
Any digital signal is fed to the ES9038Pro DAC. The 9038Pro is an 8-channel DAC which means that the CMA Fifteen sums 2 channels in the DAC to feed each (4) amplifier circuit.
The ES9038Pro output is in current mode by default, and the signal stays in its native mode from DAC to headphone with no need for voltage amplification and the attendant distortion that is often introduced with it.
The CMA Fifteen offers PCM up to (and including) 32-bit/768kHz, DSD up to 512, and full MQA decoding; you need to use one of the USB inputs for 32-bit/768kHz.
Anyone have music available at that level? Anyone? Anyone?
Does it Sound Any Good?
There’s always going to be at least one headphone that causes problems but the Questyle CMA Fifteen proved to be rather adept at driving every pair of headphones that I threw it; the HiFiMAN HE-560 and HE-6 and some of the earliest Fostex planar models required the high gain setting but otherwise what a workhorse of a headphone amplifier.
The CMA Fifteen is extremely clean and detailed sounding with enough power to drive most of my collection of headphones on low gain including heavy hitters like the first generation Beyerdynamic T1, Sennheiser HD800, and 600 ohms AKG 240s.
None of those headphones could trip the CMA Fifteen up which says a lot about the design of the amplifier.
Out of curiosity, I tried some IEMs on the high gain setting which no sane person would use for normal listening; the noise floor was definitely higher on this setting but the sound was still very clean sounding and I could hear a lot of detail without noise being a distraction.
A more realistic pairing involved a pair of the UE Live and the CMA Fifteen on low gain which resulted in a very pleasant sonic experience with some of the darkest backgrounds I’ve heard on a pair of IEMs in awhile.
For most of my evaluation, I used the HiFiMAN HE-6, Sennheiser HD800, Audeze LCD-3, Beyerdynamic T1 (2nd gen) and T5p (first generation), as well as the AKG 812’s. I would have liked to test with the Audeze LCD-5, but those were sent on to another reviewer.
I listened to all of them in balanced configuration and tried some of them using the single-ended option during my second round of testing.
My choice of headphones had a lot to do with price of the CMA Fifteen; how many people spending more than $2,500 on a DAC/Headphone Amplifier are going to pair them with entry-level headphones?
I selected the aforementioned headphones because my experience with all of them has led me to believe that they are the most revealing and least forgiving — any imperfections were going to be illuminated rather quickly with the source material.
I was pleasantly surprised to hear that the engineers at Questyle really know how to get the best out of the ESS Series chips which displayed none of the cold and clinical edge that they are known for; I really shouldn’t be that surprised considering how good the DACs in the M12 and QPR1 products are.
I began with the HE-6 and Rudolf Serkin’s Beethoven Piano Concertos and was immediately taken by the dynamic range and wonderful tonal balance of the CMA Fifteen; piano notes had so much body and impact which I really didn’t expect.
Switching to the Audeze LCD-3 on low gain mode, Mussorgsky’s Great Gate of Kiev demonstrated just how effortlessly the CMA Fifteen can go from dead silence to roaring crescendos without any form of congestion or a collapse of the soundstage.
The Beyerdynamic T1 seemed like a logical choice with Miles Davis’ Bitches Brew and the the CMA Fifteen did not disappoint.
Horns can be difficult for some headphones depending on the amplifier, but the T1/CMA Fifteen combination had texture, decay, body, and more than enough detail to make this recording come alive without any hardness on top.
Even on low gain with almost all of my headphones, I never found the need to push the volume past 10 or 11 on the dial and I quickly realized just how powerful this amplifier can be even with demanding headphones.
The Sennheiser HD800 on the other hand, was able to use nearly all of the volume control on low gain and some will probably prefer to move to the high gain setting and keep the volume a bit lower rather than push toward 2 or 3 o’clock on low gain.
Moving to the single ended connection with the HD800, the high gain mode becomes the operative choice although it still has plenty of headroom and can easily still reach levels that shouldn’t be used for longer than a few minutes.
The Big AKG and Beyer T5p have more usable volume control on single ended as well and with neither requiring the power available via the balanced connections, I’d stick with single ended for lower impedance, high sensitivity models.
I put the CMA15 through its paces with PCM files in the form of FLAC and AAC via Apple Music and Qobuz streamed via PC as well as MQA in both files and TIDAL Masters streamed from a Samsung phone using LDAC.
I found the CMA15 handled everything I threw at it with equal ease; Pairing was quick and simple and connections were solid as long as line of sight was maintained.
It’s hard to pick out one specific area where the Questyle CMA Fifteen bested all of the other headphone amplifiers in my collection, but I will concede that it demonstrates almost endless power with most headphones; it really makes it look too easy with some.
I found it be extremely clean sounding with excellent detail retrieval — but not at the expense of tonal color which is pretty amazing.
I’ve heard a few other ESS DACs that could compete with the CMA Fifteen’s sound quality but all were nearly double its asking price. Likewise, the amplifier section spares no expense and delivers plenty of noise-free power to a wide range of IEMs and headphones depending on outputs used and gain settings.
The decision to include a single-ended RCA input shows that Questyle has been listening to users because that was the single biggest complaint leveled against the CMA Twelve when it was introduced.
Just how good is the Questyle CMA Fifteen in the grand scheme of things?
I would have no issue replacing the RME ADI-2 or Bel Canto 2.7 in my current systems with one and never look back.
If you’re in the market for a really high-end (and not inexpensive) DAC/Headphone Amplifier, the Questyle CMA Fifteen needs to be at the very top of your audition list.
For more information, see our story when the CMA Fifteen was announced.
Where to buy: $2,495 at Audio46