@jwr159 Thanks for the link. Very useful discussion among people who seem well-informed about the nitty gritty.
Thanks to other posters, here. I'm learning a lot.
"A Remarkable Amplifier—A Class B Amplifier for Audiophiles"
Anyone here ever build one? Ever hear one?
Fascinating read.
"My 40-Year Love Affair with a Remarkable Amplifier—A Class B Amplifier for Audiophiles"
by Dermot Herron (2018, All About Circuits)
The Blomley amplifier was designed over forty years ago, is an alternative power amplifier design that suffers virtually no distortion, and provides a sound which has the presence often lacking in conventional amplifiers.
A modern high-quality audio system has excellent specifications and sounds almost perfect. Almost perfect, but not quite. There is one very important attribute missing in audio systems—the attribute we call “presence”. This article discusses an alternative power amplifier design with sound that often lacks in conventional amplifiers.
Note: Due to popular demand, the LTspice files for the circuit discussed here are available at the bottom of the article.
Even the best commercially available audio systems lack real presence–while the sound can be crystal clear, you would never mistake the recorded voices for real voices, or the recorded piano for a real piano. The human ear immediately knows the difference.
As listeners, even as audiophile listeners, we don’t fuss about this lack of presence because we have come to accept that what we hear from a modern audio system is as good as it gets. Yet this just isn’t true, and it doesn’t have to be accepted.
The lack of presence occurs almost entirely as a result of distortions inherent in the fundamental design of all commercial power amplifiers. Have you noticed how much clearer headphones sound? It's due to the fact that they are driven by low-powered amplifiers....
The end result of this difficult-to-understand circuitry (we are used to voltage circuits) is a Class B amplifier that has a distortion lower than 0.1% with no feedback at all. And on an oscilloscope, there is no discernible crossover distortion with no feedback.
After a little feedback is applied, there is unmeasurable intermodulation distortion, transient intermodulation distortion, and harmonic distortion. The resultant output of this amplifier is so clear that a recorded voice can easily be mistaken for a live person. Peter Blomley’s amplifier is a Class B amplifier with much better than Class A performance.
And yet Peter Blomley and his amplifier have gone virtually unrecognized in the audio world for more than 40 years. I suggest two reasons for this. First, his design was so original and so unexpected that few people understood it or took it seriously. Second, Blomley never put his design into commercial production because Plessey held the patent, so even fewer people were able to listen to it or review its performance.
Most of the audio hobbyists who constructed their own Blomley amplifier modified the design and in doing so introduced distortions. I suggest you build the original design (with perhaps just the minor modifications afforded by modern components) and listen to it. This will give you a reference sound to check any further modifications with which you might like to experiment.
Unfortunately, in ignoring the Blomley design for so long, the audio world has deprived itself of a fundamentally better amplifier. We have instead put all our efforts over the last forty years in trying to mitigate what we thought were unavoidable inherent characteristics of electronic amplifiers, particularly Class B amplifiers. The boldness of Peter Blomley as a young engineer was to question how unavoidable these characteristics really were, and to then set about designing them out of his amplifier.
Today, superb high-voltage, high-speed transistors are available which makes the Blomley amplifier even better than his 1971 version.
The original amplifier design was for a 30W amplifier with a 60V power-rail, and because of the purity, this is more than adequate for normal home use. In 1971, 100V small-signal transistors were rare, but this is no longer so and an 80V power-rail can now be used, with different transistors, increasing the power to 50W. However, high sound volumes are not needed as the sound is so exceptionally clean. The huge headroom provided with most amplifiers is there so you can play them at high volume and bury the crossover-caused intermodulation distortion in the high sound-level (quite sad really).
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Is the OP's article telling the complete story given the following AI quick search / summary? Pure Class B amplifiers inherently suffer from crossover distortion due to the 0.6V–0.7V turn-on voltage of transistors, causing a "dead zone". To eliminate this distortion while maintaining Class B efficiency, amplifiers must use biasing techniques—such as diodes or multipliers—to bring transistors to the edge of conduction, effectively creating a Class AB design. Key Methods to Eliminate Crossover Distortion Diode Biasing: Placing diodes between the base-emitter junctions of the push-pull pair keeps them slightly conducting, eliminating the dead zone. Technological Solutions Current Dumping: A design philosophy where a small Class A amplifier handles low signals and a high-power Class B "dumps" current for larger signals, eliminating the need to carefully bias the Class B stage to avoid distortion.
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greetings & kind regards may i please inquire how the tiny pocket sized inexpensive appearing amplifier as shown on diyAudio can compare to a modern unit costing thousands of dollars the size of a bread box weighing many kilograms . . thank you kindly |
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