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Questyle Audio CMA800R Headphone Amplifier

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The Questyle Audio CMA800R is a dedicated headphone amplifier quest for perfect sound.

The flexibility to add a second unit to operate in True Mono Balanced operation makes this amplifier as flexible as it gets in the realm of Headphone amplification. Strong, powerful and controlled are the thoughts this amp brings to mind. Lets not forget it can also be used as a wonderful Preamp as long as you have only one source. 

"I heard details previously buried deep in the track. The sound was dynamic, ethereal, detailed and precise...Everything you want music to be was there." Howard Gladstone, Piltron President

Questyle CMA800R Headphone Amplifier Review - March 2017 by

Hearing your music for the first time

The "Current Mode Amplification" technology, developed and designed by Questyle Audio CEO and founder Wang Fengshuo, provides the airiness and musicality of a tube amp while maintaining the speed and accuracy of transistors. This technology is subject to a PCT patent. 

In current mode amplification, the signal is amplified by modulating current instead of Voltage. It is widely applied in the high speed communication industry and the video processing industry. However, it is Questyle Audio's patented technology as applied to headphone amplifiers. 

The goals of all high performance amplifiers is low distortion and wide bandwidth. Only with ultra wide bandwidth and high speed processing can an amplifier wonderfully process sudden pulse wave signals, and achieve realistic playback of music signal with speed and transparency. 

In order to achieve this, Questyle Audio abandoned the traditional voltage mode format and developed "Current Mode Amplification." When the component is working in Current Mode, the amplifier Slew Rate (SR) achieves a linear increase as input signal amplitude increases, in direct proportion to the input signal amplitude. 

When receiving a high amplitude signal, a "Current Mode" amplifier's SR is much faster than traditional Voltage mode devices, totally eliminating TIMD and ensuring a high amplitude signal with an extremely wide linear bandwidth and an almost distortion free realistic playback. 


Work Principle

Questyle Audio's Current Mode Amplifier employs all discrete componentry in a Class A configuration in order to maximize accuracy, current capability, and consistency. To insure maximum compatibility with source units and speakers (headphones), Input and Output both work in voltage mode.

This diagram shows the input signal travling to the VCCS first; voltage mode is converted to current mode here. It then goes to Ai for amplification (in current mode). Next, it goes to I/V converter to become voltage mode again, and then is output to OPT stage to drive headphones.

Questyle Audio Work Principle Diagram CMA800R


The Questyle Audio CMA800R has a 10mm thick aluminum chassis produced by Foxconn using precise CNC tooling machines.

The upper cover and bottom chassis "mutual bit" structural design, provides the Questyle Audio CMA800R with stable heat, excellent control of sympathetic vibration and excellent shielding from RFI/EMI radiation.


Design Concept

The Quest is endless. The Questyle Audio CMA800R, the flagship Current Mode Headphone Amplifier from Questyle Audio, is a dedicated quest for perfect sound.

The Questyle Audio CMA800R implements Questyle Audio’s outstanding Current Mode Amplification TM technology, providing an ultra-low 0.00038% distortion, a wide bandwidth of 650KHz, and an 114dB Signal to Noise Ratio. These parameters are far beyond what any other existing headphone amplifiers can achieve. Beyond that, the Questyle Audio CMA800R is the world first headphone amplifier to support Mono Full Balanced operation (a bridged mono configuration for use in a dual mono application using 2 Questyle Audio CMA800R amplifiers), in full balanced mode its distortion is further reduced to less than 0.00026%! The Questyle Audio CMA800R, will definitely be a milestone of headphone amplifier design.


Traditional Voltage Mode Amplifier

Analogue amplifiers are always thought of as processing signal in voltage mode. In its circuit design, engineers subconsciously put it into a voltage or voltage related loop, and suppose this is the best solution for processing signal.

Since Fairchild produced the first commercially applied OPA uA709 in 1965, OPA technology has greatly developed, but the basic circuit structure has not been changed. This kind of amplifier is known as having a narrow frequency bandwidth, low efficiency, and when dealing with large dynamic signal, it always creates TIMD.

Some manufacturers want to break through these limitations, they give up the traditional negative feedback design and turn to new methods, which cost a great deal, while bringing other serious problems, such as unstable performance.

A totally new design and new topology is urgently required, and to bring a revolution in analogue amplification became our goal.


The Encouraging Current Mode Circuit Design Development

It is commonly understood that, a BJT (Bipolar Junction Transistor) is a current mode capable device. Suppose the entire amplification section is fully operating in Current mode, taking complete advantage of the outstanding linear and ultra-high speed capacities of the BJTs, their performance would be definitely attractive and amazing.

1) Super Linear theory

In 1975 Mr. Barrie Gilbert created the “Translinear-TL” theory, and published in ISSCC. This marks the birth of Current Mode theory. A translinear (TL) circuit is a circuit that carries out its function using the translinear principle. In TL principle, an ideal BJT Collector current log domain’s (Lc) and Vbe graph is a straight line. See the below graph, BJT Collector current increases from 1pA (1E-12) to 10mA, which is an increase of one billion times, while log (lc) and Vbe remain a good straight line! A Current Mode circuit is using this super linear feature to make up a TL loop. This is the basic theory for Current Mode’s ultra-high precision, ultra-low distortion operation.

Questyle CMA800R Super Linear Theory

2) Ultra-high speed

In a Current Mode circuit, the interelectrode capacitors in between transistors, which affect speed and bandwidth, operate at a very low impedance point (hundreds or even thousands of times less than a voltage mode amplifier). With a large amplitude current wave, the interelectrode capacitors complete their charge and discharge cycles very fast, making the efficiency much greater than that of a voltage mode circuit.

Questyle CMA800R Ultra-high Speed


The Questyle Audio CMA800R Operating Principle

Since 1989 and the 87th AES forum, when Dr. D.C Wadsworth first pointed out that a current mode circuit in audio can achieve ultra-high speed, ultra-low distortion operation, audio designers have ceaseless sought applications for current mode amplification. Some pioneering manufacturers have been developing current mode technology applications for audio, such as CAST (Current Audio Signal Transmission) technology, SATRI technology based on the BPM7110 gain module, etc. But they are mainly “non-feedback” mode, and mainly for current mode “transmission” rather than amplification. Questyle is different, we specifically focused on “amplification” instead of “transmission”, allowing the Questyle Audio CMA800R to provide much more outstanding sonic performance.

Above is the CMA800R current mode amplification circuit diagram. The circuit is consist of VCCS (Voltage Control Current Source), A(i) --Current Mode amplification module, I/V converter, OPT and Negative Feedback sections. In an electronic circuit, both voltage and current are present, neither can be missing. The Questyle Audio CMA800R signal is controlled by current so as to provide higher performance, while the input and output are in voltage mode for better compatibility with other audio devices.

From the diagram we can see, input signal will travel first to VCCS, voltage mode is converted to current mode here, then it goes to Ai for amplification (in current mode), next it goes to I/V converter to become voltage mode again, and then is output to OPT stage to drive headphones.

For better performance, in this circuit design we included a Negative Feedback loop. The impedance of the whole Negative Feedback loop is very low, and the amplification is very fast, thus the Negative Feedback process speed can be as much as 100 times faster than that in voltage mode, eliminating problems like TIMD.

The Questyle Audio CMA800R Full-Power Bandwidth is close to the Closed-loop bandwidth, converting speed increases linearly as input signal amplitude increases, these characteristics are totally different from those produced in voltage mode, allowing the Questyle Audio CMA800R to achieve ultra-low distortion and ultra-high efficiency.


The Workmanship

Current mode amplification's internal translinear-TL loop places a critical requirement on transistors. A Canadian semiconductor manufacture, Microsystems International Limited, had tried to make a current mode amplification IC, but failed on workmanship.

In a TL loop consisting of 6 transistors, even a 5uV Vbe is too much, it will cause an 0.01% harmonic distortion. Questyle's engineers studied this for over 5 years, working together with Dr. Charles a specialist from a California university who is dedicated to transistor workmanship research, selecting from lots of customized specific components, and design specific circuit structure, finally achieving success.

Questyle CMA800R Audio Precision THD vs Power

[email protected]Ω , THD vs Power


Questyle CMA800R Audio Precision FFT Spectrume Analysis

[email protected]Ω , Po=10mW FFT Spectrum Analysis


Intermodulation Distortion (IMD)

Some engineers use Sine waves to test amplifiers. They believe that, as long as the THD+N value is not high, it should be a good amplifier. But actually each music signal is made up of thousands of harmonic waves, it is expected that they will interfere each other, so IMD value is even more important as an approach to indicate a signal's real status than THD+N. “IM (Intermodulation)” means as two or more signals come together, they will interfere with the others and make up a new signal. IMD decides an amplifier’s purity, density and detail. The Questyle Audio CMA800R IMD spectrum is almost as perfect as the AP2 signal source. There are almost no mixtures.

Questyle CMA800R Audio Precision IMD Test

Po=10mW @300Ω , CCIF 19K Center frequency, 500Hz Modulation frequency IMD test


Full frequency low distortion

Ultra-wide bandwidth provides an amplifier with great sound, but ultra-low distortion is required for high frequency, otherwise the sound will be terrible. The Questyle Audio CMA800R distortion graph in all frequencies is a straight line, the value is ultra-low.

Questyle CMA800R Audio Precision Low distortion

Po=25mW @300Ω


Broadband High-speed Amplification

Only an amplifier with broadband high-speed amplification can best deal with burst pulse wave signal, and therefore reproduce with speed and clarity. The Questyle Audio CMA800R frequency response is straight line, with only a -0.3dB drop at 200KHz.

Questyle CMA800R Audio Precision Frequency Response

Po=20mW @300Ω , 20Hz-200KHz frequency response

Below is the CMA800R square wave frequency response @20KHz (Red color is input signal, purple is output signal, 300Ω loading)

Questyle CMA800R Audio Precision Frequency Response


Specific Power Supply

For an analogue amplifier, power supply plays a very important role. We work together with Plitron Manufacturing in Canada, supported by their senior designers, to specially design multiple versions of dedicated transformers, evaluate and select the best fit. On top of that, the Questyle Audio CMA800R uses Schottky rectifiers to reduce noise, and 22 35V 1000uF Nichicon FG capacitors to provide clean power.


Mono Full Balanced function

The Questyle Audio CMA800R is the world’s first headphone amplifier with Mono Full Balanced function. Two Questyle Audio CMA800Rs in “Mono” mode, each one set to “Mono Full Balanced” status, separately drive the Left and Right channels in a dual Mono configuration. In a dual Mono setup, each channels power supply and amplification is independent, this provides first class driving power, especially outstanding in driving headphones limited in sound stage or separation, or ones that are difficult to drive.

Questyle CMA800R Full Balanced function

In Mono Full Balance mode, the Questyle Audio CMA800R distortion is as low as 0.00026%. 

Questyle CMA800R Audio Precision THD vs Power Mono

1KHz @300Ω , Mono mode THD vs Power graph


The Components

The Questyle Audio CMA800R adopts best Hi-end components to ensure best sound. Here “best” means best fit, like the OPA627 operational amplification module, DALE military resistors, WIMA customized capacitors, Alps volume potentiometer, Nichicon FG capacitors, etc.

Customized WIMA capacitor

Customized WIMA capacitor

DALE military resistor

DALE military resistor


Sound Performance

Beyond good parameters and good components, good sound performance is the last but most critical factor. Before production, the Questyle Audio CMA800R was tested with various models of headphone, and were sent to many studio engineers and musicians to listen to the sound, and not until they were all satisfied with the sound, were the Questyle Audio CMA800R detailed specifications fixed and put into production.

Manuals and Guides
(Size: 301.9 KB)
Questyle CMA800R Headphone Amplifier

  • Current Mode AmplificationTM, 0.00038% ultra-low distortion and ultra-high efficient amplification
  • Balanced (XLR) input and single ended (RCA) input, Mono Full Balanced input
  • Dual 6.35mm stereo headphone jack, a 3-pin Full Balanced output
  • Pre-amplifier output
  • Mono Full Balanced operation
  • Customized Plitron toroidal transformer
  • Schottky rectifier,22pcs Nichicon 1000uF Audio specific FG capacitor filters
  • Amplification circuit uses only DALE military resistors and WIMA capacitors
  • All transistors are operating in pure Class A
  • Perfect ON/OFF Anti-Pop Noise protection and DC protection circuit design
Gain:   15.5dB
Max Output Power: 

 180mW (7.5Vrms) @300Ω, standard Stereo Mode

 710mW (15Vrms) @300Ω, Mono Mode


 114 dB, standard Stereo Mode

 118 dB, Mono Mode


 0.00038% @1kHz, 300Ω standard Stereo Mode

 0.00026% @1kHz, 300Ω Mono Mode

Frequency Response:   DC-200kHz (+0, 0.3 dB); DC-650kHz (+0, -3 dB)
Sensitivity:   1.2Vrms
Impedance:   47KΩ
Input:   XLR stereo, RCA Stereo, and XLR Mono Full Balance input 

 Dual 6.35mm Stereo headphone Jacks,

 a XLR Mono Full Balance output,

 A pair RCA Pre-amp output 

Work Status:   

 Pure Class A 


 100-120Vor 220-230V, Internal switchable 

Power Consumption:    13W 
Dimension:    330 x 300 x 55 mm

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