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Dersom noen skulle ha interesse av å lese om teknologien (tripath) som Bel Canto (eVo 2) bygger sin nevnte forsterker på så kommer den her:
The Bel Canto Design eVo digital output stage is of unique simplicity. The output uses 2 N- channel MOSFET switches which are switched between the power supply rails.
These switches turn on and off within 30 billions of a second and provide an on resistance path to the supply of less than 65 thousands of an ohm.
These switches switch alternately between the supplies at a rate
that averages over 600 thousand cycles per second (600 kHz). When no audio signal is present the ratio between the time at the positive supply and the negative is balanced to provide no audio frequency output. The switching stage is isolated from the loudspeaker by a single Inductor/Capacitor (LC) filter that removes energy above 80 kHz.
Furthermore, the digital power processor adds small levels of high frequency dither to insure that an inherently linear output stage characteristic is maintained from very low to very high output
levels.
The audio frequency information modulates the output stage by changing the time relationship between the positive and negative supply rails.
The critical timing information is controlled by the digital power processor and the effective switching frequency is changed over a
200 kHz to 1500 kHz range.
This spreads the digital energy created by the amplifier over a wide
bandwidth, similar to spread spectrum technology, greatly reducing the energy at any one frequency.
This permits using a simple 80Khz LC filter to remove the digital energy and maintains low cost and excellent phase response. Feedback around the output switches is taken from the common node of the output switches before the LC filter and fed back to the digital power processor.
This feedback is used to insure that any variations in the switching speed of each output device are compensated for, optimizing the linearity of the output stage.
The eVo output stage does not suffer from the distortion mechanisms of analog output stages; crossover distortion, thermal bias wander and transconductance variations.
The audio information is carried in the complex modulation of dithered switching edges.
The digital processor controls the modulation of the output switches. The typical compromises between output stage efficiency, complexity and linearity and cost no longer apply.
The eVo output stage is over 90% efficient, uses only 2 N type output devices and maintains extremely high linearity and low output impedance for good power delivery and control of the loudspeaker.
The digital power processor insures that high frequency energy and audio band performance are excellent without the problems of older class-D type switching architectures.
Important measures of amplifier performance such as Total Harmonic Distortion, Noise and most importantly Inter Modulation
Distortion levels are extremely low across the audio band at all power levels.
eVo Digital Power Processor versus Class D
Traditional switching amplifiers have used what is termed a Class D architecture.
This architecture uses a Pulse Width Modulation algorithm to control the output stage switches.
These algorithms are generated with relatively simple analog processing and a crude digital to analog conversion mechanism based on a fixed frequency triangle wave.
Traditional analog feedback is then used to reduce the distortion produced by the analog processing and output switchimperfections to acceptable levels. This approach has numerous drawbacks and can produce unacceptable levels of THD and IMD.
The fixed frequency of operation also requires extreme
measures in designing the output filter to insure that switching noise is low enough.
This can result in frequency response changes between 4 and 8 ohm loudspeaker loads and large phase deviations at high frequencies.
The eVo architecture insures extremely linear phase response, low levels of IM distortion and has a THD performance which consists of low levels of low-order harmonics in a very natural descending progression, much like a single-ended amplifier produces. However, the distortion levels of the eVo amplifier are typically 10 to 100 times lower than a SE triode amplifier.
The sonic signature of the eVo amplifier is virtually gone, leaving the musical message intact.
Analog Signal Processing
All analog signal processing in the Bel Canto eVo architecture occurs at small signal levels using 15 volt and 5 volt analog circuits. These stages are powered by low noise regulated supplies and use the latest audio grade amplifiers, resistors and capacitors.
The analog input is received using a true instrumentation amplifier to allow ideal processing of both single-ended and balanced input signals.
The eVo architecture confines the analog processing to small signal where analog processing is best, noise is reduced and analog distortion mechanisms are minimized.
This also insures that the eVo amplifier can be used within todays analog based system architectures without extra expense or performance compromise.
The Digital Power Processor contains both CMOS analog and digital processing to convert the analog input signals to a digital bit stream for processing and driving the output stage switches.
High voltage DMOS drivers then drive the output switches for controlled switching speed of less than 30 nS.
The slew-rate of the output stage is over 6000 Volts per microsecond, more than 10 times faster than any analog power amplifier.
No feedback is taken from the analog output of the
power amplifier after the LC filter.
The output filter uses a low distortion high performance
gapped toroidal iron-core inductor and low-loss capacitor.
Overload and Protection Circuitry
The Digital Power Processor also provides unique advantages in the overload and protection circuitry of the eVo amplifier. The eVo amplifier uses the digital signal processor to sense
amplifier clipping.
If clipping is sensed high frequency dither is added to insure that the clipping performance is soft and does not produce the extreme high harmonics that solid state amplifiers suffer from. These harmonics can result in unpleasant sonic consequences, producing buzzy or
harsh sounds when driven into clipping.
The soft clipping characteristic of the eVo amplifier mimics the soft tube overload characteristic, preventing the harshness that most solid state amplifiers suffer from.
This soft clipping does not cause any compromise in the performance of the amplifier at levels below clipping. Typical, analog-based, soft clipping circuits in solid state
amplifiers achieve the soft clipping characteristics at the expense of distortion performance below
clipping. This is not the case with the eVo amplifier.
Mvh.KW