Is it a rocket!!!
The Hifi Trajectory Of Class D Amplifiers
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I bought my first digital SLR camera back in 2005. Film SLR cameras were still king back then. Longtime film camera hobbyists and pros thumbed their noses at digital. Ten years later, film cameras have been surpassed by digital cameras and are nearly extinct. Millions of people use cameras. The market was already in place for anyone that would advance the technology of digital photography.
With Class D amps, you don't have a marketplace the size of the camera marketplace. There doesn't seem to be enough economic incentive to spend the necessary research dollars to advance the technology to get the same sort of improvement trajectory that digital photography has enjoyed.
Anyone care to speculate how long it will take for Class D amps to consistently rival the best tube, Class A and Class A/B across the board....and do it without resorting to the stratospheric prices that current non-Class D amps are priced at.
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I bought my first digital SLR camera back in 2005. Film SLR cameras were still king back then. Longtime film camera hobbyists and pros thumbed their noses at digital. Ten years later, film cameras have been surpassed by digital cameras and are nearly extinct. Millions of people use cameras. The market was already in place for anyone that would advance the technology of digital photography.
With Class D amps, you don't have a marketplace the size of the camera marketplace. There doesn't seem to be enough economic incentive to spend the necessary research dollars to advance the technology to get the same sort of improvement trajectory that digital photography has enjoyed.
Anyone care to speculate how long it will take for Class D amps to consistently rival the best tube, Class A and Class A/B across the board....and do it without resorting to the stratospheric prices that current non-Class D amps are priced at.
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- 42 posts total
Ten years later, film cameras have been surpassed by digital cameras and are nearly extinct.Mitch4t, I'm not sure I agree with your on this statement. Yes, digital cameras are everywhere & millions of people have gotten into "photography" as a result but IMO the film vs. digital camera is the same argument as .WAV vs .MP3 music files. The high compression of music files has made the file size smaller, totally wrecked the sonic quality but has afforded great convenience to the public to the point that 100s of songs can be stored on your portable device & played back at will. Digital photography too has made it very convenient to take photos without thinking much about the photograph to be taken because it's so convenient to delete the bad photos & keep the better ones. People are mindlessly taking photos because they can & the quality of photos (in terms of composition, lighting, artistic content), in general, has gone down just as fast. It's a great stride forward in convenience but many steps back in art of photography. Take a look at these photos - they are all take by a FILM camera (no digital). In fact, it is my understanding that Arizona Highways magazine does not accept any digital photos as their resolution is not good enough for even an 18X10 print! The photo quality is superb & very much like what the human eye sees - all boundaries are gradual; not stark/abrupt as in a digital camera.... http://www.arizonahighways.com/photography/photo-archive |
Bombaywalla, comparison film vs. digital SLR is very unfortunate here, since class D is purely analog with unlimited resolution. Still, you can take equivalent quality pictures using medium frame size film camera for much less money than digital, but in case of 35mm frame film camera has no chance. Digital cameras have better resolution, lower noise, bigger dynamic range and much higher sensitivity (ISO) not to mention overall convenience. http://petapixel.com/2015/05/26/film-vs-digital-a-comparison-of-the-advantages-and-disadvantages/ |
The premise that class d amps haven't "arrived" is flawed. Many people love them, in fact many have dumped their Pass, Bryston, ARC, etc. amps in favor of class d. All one needs to do is read through the various Hypex class d threads all over the internet to see this. It isn't a question of if, or even when, class d will take its place at the table, it has already been accomplished. The objective performance of class d amps is now significantly better than most ss and surely all tube amps. Of course there will be those with vested interests who will poo-poo class d, and there are those who prefer the distortion profile of tube amps. Ultimately, it comes down to personal preference and subjective tastes, and as has been demonstrated in the market place, class d has shown it has not only arrived, but displacing traditional ss and tube amps everywhere one looks... |
Here’s the “hold the baloney” sandwich on Class D Amplifiers. An expert from Lenard Audio. Class D amplifiers are described as PWD Pulse Width Modulation amplifiers. Class D is similar to a Switch Mode Power supply. Switch mode power supplies and Class D amplifiers are low mass, generate very little heat and approx 90% efficient. The majority of small amplifiers less that 20 Watts in computers and domestic application including TVs etc are now Class D amplifiers. Above 20 Watt the complexity and problems of Class D increase exponentially. Similar to switch mode power supplies, Class D amplifiers are virtually un-serviceable and life after 7 years considered a blessing. Switching on and off a light bulb, electric motor, electric heater etc at high speed to control power is not rocket science to understand. With a little imagination a speaker could be switched on and off across 2 batteries and by varying the on time compared to the off time (providing the switching speed is above hearing range) the mass of the cone will average the energy to represent an audio signal. Pre 1970 Valve technology reigned supreme. Outside of experimental computers the first transistors were used in small cheap radios which is how the Japanese electronics industry and Sony began. Transistors do and not have a linear function similar to valves, but are ideally suited to switching on and off. Class B analogue transistor amplifiers above 10 Watts were originally unreliable. It was assumed that transistors would not be suited for making high powered class AB amplifiers. In 1964 Clive Sinclair an electronic inventive genius along with fellow engineer Gordon Edge developed the first PWM amplifier. The X-10 was marketed as 10 Watts but only produced 2 to 3 Watts. The Z-12 arrived shortly later which reliably produced 12 Watts, and the race was on. Almost every young electronic audio enthusiast started experimenting with PWM amplifiers. It was believed that PWM amplifiers capable of 100s of Watts would be available at low cost before a man would set foot on the moon. Similar to Dr Frankenstein everyone was originally unaware of the monstrous lurking problems that were about to be unleashed. Any radio or TV in close vicinity to a PWM amplifier was blocked out by the Rf noise interference generated by the high frequency switching of the transistors. Test equipment capable of analysing switching frequency rise times that approached the limits of physics was not readily available. Government communication authorities quickly outlawed the use of any device that interfered with Rf transmissions. Another 30 years would pass before the science for controlling PWM Rf noise radiation was better understood. Very few high power PWM amplifiers today are CE Communication emissioncertified. Understanding how a PWM amplifier works requires a lateral shift in thinking, but once the basic principle is seen it appears almost obvious. PWM does not require separate switching for each half of the wave form as in the first pic. A fixed high frequency square wave 100kHz to 1MHz is width modulated by the audio sine wave. At the output is a filter stopping everything above 20kHz from getting to the speaker. The above pic is expanded to show only 16 pulses across an audio sine wave. When the square pulse widths are equal the averaged energy output is zero. As the pulse widths become wider than equal the averaged energy shifts toward the +Ve half of the audio sine wave. As the pulse widths become less than equal the averaged energy shifts toward -Ve half of the audio sine wave. But how is this achieved? (1) To make the transition from a audio sine wave to a fixed 100kHz to 1MHz modulated square wave that simulates the energy of the sine wave, requires an intermediate step. First, a fixed 100kHz to 1MHz triangle wave is generated. The triangular wave must be approx x 100 the highest audio frequency. As the sine wave moves across the high frequency triangle wave a comparator recognises which part of the sine wave is above or below the points crossed on the triangle wave. (2) As the triangle wave is crossed by the sine wave the MOS-FETs are turned on or off generating a high energy square wave of varying width. The MOS-FETs are not capable of turning on and off instantly. In the real world the speed of light is a theoretical concept. The Slew of the MOS-FETs governs how quickly the change from off to on and off again can happen. (3) This transition from off to on represents the leading or trailing edge of an extreme high frequency which is magnitudes higher than the 100KHz to 1MHz fixed switching frequency. As the corners of the leading and trailing edges of the square wave make the transition from vertical to horizontal Rf ringing noise is generated. This Rf ringing also creates secondary problems inside the MOS-FETs that result in excessive heating and potential breakdowns. The lower part of the above pic shows a more realistic view of the hi frequency square wave in comparison the comparatively low frequency audio sine wave. It clearly shows the noise of the switching frequency imposed on the audio sine wave that has to be filtered out. The high frequency modulating frequency has to be filtered out leaving the resultant energy of the amplified audio. The LPF Low pass filter only allows everything below 20kHz to get to the speaker. Class D amplifiers are similar to the switch mode power supplies in computers and therefore non user serviceable. Failures are simply dealt with by warranty replacement or purchasing a new amplifier. The technology of professional high power Class D amplifiers is so complex and fragile that reliable operation of after 7 years should not be expected. A deeper technical understanding of PWM amplifiers and their limitations is on this PDF published by component manufacturer IR (International Rectifier) sound.whsites.net PWM An excellent technical review of PWM problems and solutions. |
- 42 posts total