REVIEW: QUESTYLE ‘GOLD STACK’ REFERENCE SYSTEM
If you're looking for the ultimate in Head-Fi listening, the 'Gold Stack' Reference System from Questyle should be number one on your audition list.
CMA800P Preamplifier, $5,199
CAS192D Digital-to-Analogue Converter, $4,299
CMA800R Headphone Stereo / Mono Amplifier, $4,299 (each)
From a very young age, Wang Fengshuo (Jason Wang) was always passionate about music and electronics. He was seven years old when he had his first HiFi listening experience. From that moment he was hooked.
He eventually majored in Electronics Engineering, at university. He became fixated with the notion that the current standards and designs in audio amplification systems were not perfect and wondered what more there might be.
Whilst working on current-mode communication circuits, he built a device for an experiment. It wasn’t built correctly, and so wasn’t fit for purpose. But it wasn’t a complete failure however, as Wang realised that the device he had built was capable of high speed audio amplification via current-mode, instead of typical voltage amplification.
He persevered. Most students love their time off during the summer, but not Wang. Instead of going home over the 2004 Summer holidays, he and his team worked tirelessly to determine the true potential of current-mode audio amplification. Whilst a few audio companies had used current-mode for audio transmission, it had not yet been used for amplification.
That summer, the first current-mode audio amplifier was born.
Since its inception, current-mode amplification has seen little to no use in the manufacturing world; most brands stick to the traditional means of voltage-amplification that we know and love.
As Wang spent years pursuing his passion, audiophiles sat up and took notice of his achievements with his unusual amplification systems. He began by selling his creations out of his own home. In 2012, such success meant he could no longer handle the demand for the amplifier by himself anymore, and the Questyle Audio brand was born.
Online message boards have long since debated the positives and negatives of different implementations of current-mode amplification. There are a select few that worship the idea of fast-slew rate. Some even say that our usual gripes with damping factor and output impedance are no longer an issue.
While Questyle has only been around for a few years, its unusual engineering principles and approach to audio have earned the brand a fast climb into the audiophile world. They made quite a splash with the QP1R portable player in the Head-Fi and Portable Audio scene, and have earned the company’s stripes accordingly.
After eyeing what’s become known as the “Gold Stack” at Melbourne’s Tivoli HiFi, the staff were generous enough to loan us what is currently the flagship offering from Questyle: an entire stack of the brand’s top-end goodies.
The stack consists of a DSD DAC, a pre-amp, and two balanced amplifiers. Each of them is the reference “Golden” edition. The main difference (other than the sexy exterior colour), is the PCB inside, which is a custom-built ceramic unit from Roberts.
Let’s start from the top.
CAS192D Digital-to-Analogue Converter
The CAS 192D is the flagship current-mode DAC from Questyle and it’s also the first link in this very unique chain.
It boasts a solid aluminium chassis, CNC machined by Foxconn. The size, dimensions and materials are the same across the entire range covered in this review. The entire casing is hefty and thick, and Questyle claim this offers control of sympathetic vibration, and excellent shielding of RFI/EMI radiation.
The front of the device offers a single colour LCD display and four buttons. At the rear, there is an array of inputs including optical, coax, and USB - one of each. Outputs include balanced XLR and unbalanced RCA.
Despite the unassuming exterior, there are a few neat tricks that separate this DAC from the pack.
Primarily is the DAC’s ability to decode “True DSD”, as opposed to DSD over PCM. Questyle claim that a lot of run-of-the-mill DSD DACs will convert to PCM before piping the audio through the outputs, whereas with this DAC (and use of the proprietary driver, software package and filtering), DSD files will never be converted to PCM before they reach the headphones.
Also, Questyle has an upgraded FIR filter claiming:
Currently the majority of DACs use FIR (finite impulse response) digital filters, but research and testing has shown that our ears are very sensitive to the pre-ring that FIR digital filters add to the impulse wave, making the music sound incoherent and unnatural. The Questyle Audio CAS192D offers the more advanced IIR digital filter, which completely eliminates the pre-ring from the impulse wave producing a more natural sound,
There are a few other goodies packed into the unit, such as 3 x asynchronous clocks, 2 x upsampling clocks, a pretty serious power supply, and the famous Wolfson WM8741 DAC chip for PCM playback (used in products such as the Audio-gd NFB-2.1 and the ALO Continental dual mono DAC/Amp).
After booting this unit up, the user is greeted with a splash screen. It will take a few seconds to prepare itself, and perform internal testing. It will then flash “ready to use” on the display.
Setup wasn’t complicated - but required a specific driver to be downloaded from the Questyle Audio website. For PCM and general playback, we found that any software was happy to be compatible with the DAC directly.
For “True DSD” playback, we had to download Jriver Media Center. Installation was a breeze, and the CAS192D and JRMC talk seamlessly once they are both up and running. We have been told that JRMC is required for DSD playback, but were unable to test if other software packages would work.
The CAS192D was simple enough to use, and happily provided both balanced and unbalanced signal at the same time.
The unit will stay active even when in “standby” mode, which was a little puzzling, as we had to keep telling our PC that the DAC had been switched off.
It’s a neat device that does exactly what it says on the tin. There is deep and unique functionality for those who seek it, and unique internal design philosophy, but fairly useful features as well.
Considering its extensive I/O possibilities, the DAC would be just at home in a high-end HiFi systems as it is in a dedicated Head-Fi rig.
Interestingly, the flagship current-mode preamplifier from Questyle was originally designed and commissioned for STAX, specifically for their flagship SR-009 Electrostatic Earspeakers.
Originally unveiled in May of 2014 at the Munich High End show, Stax proved its support of this preamp by providing an entire SR-009 system to be displayed with the CMA800P for the launch.
Physically, the CMA800P is cut from the same cloth that that the CAS192D DAC is, with a similar weight, the same physical dimensions, and a familiar aesthetic all the way down to the aluminium casing, which was selected by Questyle to maintain proper temperature control).
But, that’s where the similarities between the two products end. The front panel of the CMA800P is simple: one giant knob for input selection, another for volume, and some LED lights to display the current input selections.
The CMA800P is a highly versatile preamp, and with an array of inputs and outputs.
At the rear of the unit, inputs include 1 x balanced input (2 x XLR) and 1 x unbalanced input (2 x RCA), along with 1 x balanced output (2 x XLR) and 1 x unbalanced output (2 x XLR).
It’s convenient to be able to quickly switch between a balanced solid state preamp and a tube preamp for sound comparisons. The switching is seamless with no delay, so once both sources are volume matched, the comparisons were made simple.
During our listening tests, the CMA800P was a top performer. Even at lower volumes, there were no channel imbalance issues, and no clicks or pops when selecting sources which you would expect from a high-end product.
To my ears, the CMA800P provided no colouration to the sound at all. It faithfully amplified any source input (balanced or unbalanced), and left the sound basically untouched. It provided clean, undistorted and raw amplification, a perfect match for the pair of CMA800R amplifiers that we had paired with it.
CMA800R Headphone Stereo / Mono Amplifier
The final link of the chain in the ‘Gold Stack’, the CMA800R is the flagship headphone amplifier from Questyle Audio.
Much like the CAS192D DAC and the CMA800P, it also utilises Questyle’s Current Mode amplification system.
The CMA800R features a razor- flat frequency response from 5hz to a number far greater than multiple times the limit of human hearing.
It also claims to be the first headphone amplifier in the world to offer “Mono Full Balanced” output.
Interestingly, instead of using a standard 4-pin balanced headphone socket to plug into, we instead found a generic 3-pin XLR instead. The reason behind this, according to Questyle is:
To create a proper balanced output, a stereo amp is required for each channel. Rather than compromise by using a transformer or resistors, Questyle takes advantage of this by allowing you to switch two Questyle Audio CMA800Rs into “Mono” mode, putting each one into a “Mono Full Balanced” configuration, effectively bridging them in a “Dual Mono” set up,
Effectively, it means that Questyle recommend having two of these amplifiers paired together to create one combined output, which is exactly what we did for our listening.
There are both positives and negatives to this. The immediately obvious positive is that the full mono balanced configuration delivers four times the power that a single CMA800R would deliver in unbalanced mode. There is also individual channel control of left and right channels, while having two completely separate mono amplifiers guarantees complete channel separation.
The compatible headphone cables for this configuration are fascinating. Rather than a single cable, there’s actually two XLR cables combined together; one for each driver of the headphones. Having each individual driver of a headphone wired into its very own full-size amplifier is really something to savour.
There are pitfalls however. Any existing 4-pin balanced headphone cables will not be compatible. Again, Tivoli HiFi was generous enough to loan me a specific cable for my Audeze headphones, but unfortunately my Sennheiser HD800S balanced cable was not compatible with this amplifier at all.
It also has to be mentioned that the idea of having to own two CMA800Rs to achieve balanced amplification may be a slightly difficult pill to swallow for some, especially when compared to the many alternative balanced amplifier options on the market.
Ultimately though, all this comes down to just one question. How does it all sound?
Whilst I quickly discovered it’s best not suited for sensitive IEM use, it does scale well over a range of different headphones and driver types.
Impressions with Audeze LCD 2
With the use of a mini-XLR to full-size XLR headphone cable which was compatible with the balanced output of the CMA800R, we were able to make the planar connection.
I found it best to keep the amplifiers at full volume, and to adjust the preamp output as a volume adjustment.
The power-thirsty planars were easily satisfied, and there was more than enough headroom to spare.
The accuracy that I found during testing with the HD800S was present here again and the true nature of the LCD 2 was brought into the light once more. Bass was full, flowing, and deep-reaching. Vocals were smooth, and without piercing treble; the headphones were being heard exactly as they were supposed to.
The LCD 2 were powered faithfully, and with plenty of headroom. There were no hints of distortion, no wonky frequency dips, and no signs of the headphone being underpowered. Another great matching.
Impressions with Sennheiser HD800S
Noteworthy is that the “800” in the amplifier’s model number is because it was designed with driving Sennheiser HD800 headphones in mind. Luckily, we had a pair of HD800S headphones from Sennheiser on-hand to test.
Whilst not as notoriously fussy as its younger sibling (HD800), the Sennheiser HD800S is still quite demanding when it comes to amplification. Thankfully, the CMA800R is more than happy to come to the party.
The characteristics of the headphone could be heard with absolute clarity. There were no audible issues with damping, no detectable colouration of the sound, and no bloating in the bass.
Tonal accuracy was spot on. The voicing ability of the headphones was brought to full light.
The matching with the HD800S was phenomenal. A pairing that I believe may even rival Sennheiser’s own HDVD800.
Details and stereo separation were some of the best I’ve have ever heard this headphone produce. The imaging and soundstage were simply immaculate.
If you’ve been searching for the perfect matching amplifier for your HD800 or HD800S, then look no further. The Sennheiser flagship is certainly being pushed to its full potential here.
But of course, for the balanced output you will need two CMA800Rs.
The Whole Stack
Once it all comes together, there are a few things that are worth noting.
Firstly, the visual statement and aesthetic of the stack is one that means business. From the first glance, it becomes immediately obvious that this is pitched squarely at the serious enthusiast or discerning buyer.
The sheer versatility of the stack is incredible. Not only is it completely self-sufficient, but each device has such an epic array of inputs and outputs. The stack integrates into the rest of my gear.
Tube preamp? No problem. Digital EQ? Sure thing. I was even able to A/B test some other preamps I had, and with perfect volume matching. The stack does a lot more than just what it says on the tin.
If you’re willing to shell out for the entire stack, which is certainly no cheap task at just north of $18,000 by my calculations, then what you will receive is an incredibly high quality, versatile setup that can faithfully power a wide range of headphones.
Make no mistake, this is high-end product. If you ever find yourself searching for an all-in-one setup with full mono balanced outputs, switchable FIR digital filters, True DSD compatibility, and a stunning finish, you’ve just found it with the Questyle Audio ‘Gold Stack’.
For more information visit the Questyle Audio brand page.
Constantly keeping himself busy, Matthew is a production manager, Brazilian jiu-jitsu blue belt, Head-Fi fanatic, coffee enthusiast and all-round cool Dad.