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Articles
Welcome to our articles page, where you’ll find a wealth of information on everything audio-related. Our articles cover various topics that will appeal to audiophiles of all levels.
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The New nx2-Amplifier: a 100W CFA Power Amp
A new high performance 100W CFA amplifier. The nx2 produces >100W into 8 ohms and >200W into 4 Ohms both channels driven. At 100W into 8 ohms, the measured distortion is below 30ppm while at 200W, it is below 40ppm. The amplifier features 700ns rise/fall times and an EF2 output stage using three pairs of…
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H.S. Black: Feedback
Feedback, or its application by humans as control theory, despite the protestations of audio designers that eschew its use, is an entirely natural phenomena. Every time you reach out to pick up an object, get up and walk around, or write something on a piece of paper, feedback data from multiple body sensors are being…
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Measuring TIM
This paper by Leinonen, Otala and Curl investigates the measurement of TIM, a hot topic in the 1970’s and early ’80’s after its potential to cause sonic degradation by the incorrect application of feedback around high loop gain solid state amplifiers. Now days (2017), there is a very complete and thoroughly in-depth understanding of TIM…
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A Concise Overview of TIM by Bob Cordell
This set of articles was written in the early 1980’s by Bob Cordell, a few years after Matti Otala identified TIM (Transient Inter-Modulation) as the probable cause of sonic imperfections in high feedback solid state amplifiers in the 1970’s. Otala’s paper sent shock waves through the amplifier design community but sadly it ended up ‘subjectivizing’…
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The Monolithic Op-Amp: A Tutorial Study
This was an invited paper at the ISSCC in 1974 by James Solomon, who at the time worked for National Semiconductor (acquired in 2011 by TI). Those were heady days in semiconductors, with major process and circuit design breakthroughs taking place at breakneck speed. The general purpose microprocessors’ pivotal role in powering the Apple II…
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Marshall Leach Opamp Tutorial
Marshall Leach (RIP) was a Professor of Electrical Engineering at Georgia Tech University best known for his Leach Amplifier which he used as a practical vehicle for teaching his students the finer details of analog design, feedback, thermal compensation and power electronics. Hundreds of Leach Amplifiers were built over the years by his students,…
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The Alexander Amplifier
Mark Alexander’s eponymous creation was an early example of a high performance CFA amplifier and used an ADI integrated opamp and IGBT output devices in a novel circuit configuration that, at the time, yielded vanishingly low distortion and blistering speed. The ‘Alexander’ amplifier has been recycled by practitioners numerous times since its initial publication with…
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12 point checklist for anyone using opamps in an audio design
Opamp User Guide V1.0.pdf
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An Overview Of SID and TIM, Walt Jung et al
This series of articles on TIM and SID (and subsequent AES paper), were authored by Walter G. Jung and published between 1977 and 1979 in ‘The Audio Amateur’. It should be read in the context of amplifier design as it stood in the late 1970’s: a clear understanding of the mechanism was only just beginning…
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X-Altra Mini One Line Preamplifier
The X-Altra Mini One is a simple line preamplifer based on the National Semiconductor LM4562 (also known as the LME49720) that I built around 2008 and which served me well until about 2014 when it was replaced with newer more sophisticated designs. Nevertheless, this simple preamp sounded very good, and thanks to the LM4562 (which…
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Hifisonix Solid State Loudspeaker Relay
On big power amplifiers, conventional electromechanical relays leave much to be desired when it comes to their ability to reliably switch fault level currents in the event of a catastrophic amplifier fault. In a worst case situation (and I speak from experience), one of the output devices fails short circuit, placing the full amplifier rail voltage across the loudspeaker terminals. Relay…