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Remembering W. Marshall Leach Jr. (and his low-TIM amp)

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Rich Pell
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re: Remembering W. Marshall Leach Jr. (and his low-TIM amp)
Rich Pell   1/31/2011 9:28:42 PM
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Here's "more on Leach and amplifier design" from an Audio DesignLine reader (who gave permission to include his name): Yes I built all the Leach amps and respected his design skills. Interesting to note late in his career Leach took an interest in classic Dynaco tube amps and modeled them in SPICE. Others to check out are the British engineers John Linsley-Hood and Malcolm Hawksford, USA designers Nelson Pass and Bob Cordell, and the tube guys from Audio Research. You may wish to investigate Australian Hugh Dean (Aksaonline.com) who is making some interesting progress in tailoring the harmonic profile of power amps to emphasise even harmonics. His stuff is not cultic nonsense, but well-engineered, reliable, and proven by SPICE and measurement. As we head toward the class-D era, for my money the best amps are still bipolar BJT designs. Leach did much to further the art. Julian Driscoll Manager DSCAPE AES M16662

kendallcp
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re: Remembering W. Marshall Leach Jr. (and his low-TIM amp)
kendallcp   12/23/2010 9:59:41 AM
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Yes, Leach was truly one of the giants of audio electronics history. The obsession with TIM triggered a new wave of audio design, but we eventually found out that it was just another name for the (predictable) modulation of gain caused by the gradual onset of slew-rate-limiting mechanisms internal to the amplifier. These days there's no excuse for building an audio amplifier that exhibits TIM, even if you want to use the traditional forms of amplifier circuit. I had the 'gunshot' experience with an early technology lithium thCl backup battery connected up with a reversed charging protection diode. My head was inside the equipment rack at the time! Took ages for my ear to recover...

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