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.
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.
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.
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.
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.
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.
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.