John linsley hood was a famous british amplifier designer. Nchannel dmosfet output stage with improved linearity. Mr linsley hoods amended circuit of his class a amplifier. However, if v bb v be, i cq 0 and the amplifier is operating as class ab.
As a consequence, newer versions, permutations and. Cc configuration of section d4, where r e is now zero and the dc source is v cc2. An input signal waveform will cause the transistors to operate as normal in their active region thereby eliminating any crossover distortion present in pure class b amplifier. The hifi engine library database contains model information, images and free, downloadable owners manuals, service manuals and product catalogues for amplifiers, preamplifiers, poweramplifiers, equalizers, processors, tape decks, tuners, cd players and loudspeakers etc. The various documentsmanuals are provided as general guides for. John laurence linsleyhood 1925 in wandsworth, london 11 march 2004 in taunton, somerset was an english electronics engineer and designer of audio components. The radford valve amplifiers the leak tl12 the mullard 510 and 520 designs. This circuit was published in wireless world issue of july 1970, following an. Simple class a amplifier, wireless world, april 1969, p 148. The site focuses on variations of an amplifier developed by john linsley hood, or jlh as he is often referred to. John linsley hood 1450 owners manual, service manuals and schematics are for reference only and the vinyl engine bears no responsibility for errors or other inaccuracies. John linsley hood published an update to the amplifier in 1996 that addressed bias stability issues, parts substitutions, and provided a version that had a directcoupled output, eliminating the output capacitor. The right of john linsley hood to be identified as the author of this work has been asserted in. In other words, both classa plus classab output stages in a single circuit.
Its performance determines largely the performance of any audio system. Graham maynards gem amplifier web site original gem classaab circuit dated 8th july 2005. John linsley hood amplifier repairs john linsley hood 75w amplifier. Copies of the original articles and additional design and construction information. It uses just four transistors, one input level pnp, a mid powered npn for phase. This module shows how to simply calculate the values needed to make a working amplifier that has.
Albinson at the fiftieth convention of the audio engineering society, in the summer of 1975, and a technical description was given by. Coates 2007 2012 power amplifiers introduction to power amplifiers power amplifiers amplifier circuits form the basis of most electronic systems, many of which need to produce high power to drive some output device. Quiescent current stability in pushpull output systems. The audio amplifier is at the heart of audio design.
A paul kemble web page john linsley hood preamp designs. He then described a class a power amplifier using three gain stages of bipolar transistors in a. The right of john linsley hood to be identified as the author of this work has been. Aliexpress ebay john lindsey hood 1969 class a amp. April 1969 linsley hood class a 10 watts 1975 marshall leach. Jlh came up with quite a brilliant little class a design which was the subject of a wireless world article back in 1969, and is still a reference today. The current debate, among the more reactionary of the.
At the same time, it was in many ways the same amplifier, the measured performance being very similar. His most famous design was his simple but effective class a amplifier but he also published many other designs in the late early 1990s i started using a passive preamp for line level sources in combination with rotel power amps. The gem is an audio power amplifier embodying simultaneously active class a. Dont listen to the naysayers, a class a amplifier will work just fine providing you specify your heatsinks and power supply accordingly. John linsley hood is widely regarded as the finest audio designer around, and pioneered design in the postvalve era. The design was published in wireless world in 1969 april 1969 issue, p. A zipfile of data on jlhs modular pre amplifier design wireless world article, july 1969, contemporary to the simple class a power amp design published in. This very small diode biasing voltage causes both transistors to slightly conduct even when no input signal is present. Best value hood 1969 class a amplifier great deals on. During the past few years a number of excellent designs have been published for domestic audio amplifiers. In 1992 i came up with the idea of an nchannel only output stage using switching or dmosfets, based upon a bipolar output circuit introduced by john linsley hood in his simple class a amplifier1.
The class ab amplifier circuit is a compromise between the class a and the class b configurations. Obviously this meant i had a requirement for an riaa preamp and i settled upon a diy kit of a jlh design. John linsley hood simple class a amplifier designs 1969, 1996. Hood 10 watt class a npn output transistors only very high frequency driver transistors. The second edition includes new material on the latest developments in the field. Valve and transistor audio amplifiers, hood, john linsley. However, some of these designs are now rendered obsolescent by changes in the availability. Both the price and quality of these amplifiers result from the operation of their output stages in. John linsleyhood published an update to the amplifier in 1996 that addressed bias stability issues, parts substitutions, and provided a version that had a directcoupled output, eliminating the output capacitor. Class a amplifier design introduction to amplifier design basic design process. Chapter 4 valve audio amplifier layouts 57 singleended vs.
Here is my take on a john linsley hood 1969 class a power amplifier. John linsley hood k1500 shunt feedback mm and mc riaa. The diyaudio diyab class ab power amplifier or honey badger as we call it at diyaudio hq was designed to fill the needs of members that require a high power amplifier with similar capabilities and characteristics to those found most in modern, expensive high end commercial amplifiers. Download it once and read it on your kindle device, pc, phones or tablets. Use features like bookmarks, note taking and highlighting while reading valve and transistor audio amplifiers. Another compromise is the socalled nonswitching amplifier, with its output devices clamped to pass a minimum current. John linsley hood amplifier completed page 5 headphone. The nelson pass zen amp and john linsleyhoods simple classa amp, and alternative amps such as the circlotron, otl and srpp. Yes, you will heat up the room, but so does your pc, and that does useful work without anyone complaining of the. If youd asked me last week when i was constructing wordsworths amp id have gladly taken photos of both sides of the board for you but ive completed the job now and am about to send the. I havent popped the hood yet, but i just ordered my own. After two and a half decades, john linsleyhoods classa power amp is still rated. The cause was the fet that feeds the input differential pair common emitters had gone o\c robbing them of bias, replacement sorted it.
Linsleyhood did listening comparisons with his 1969 class a amplifier and commented that his test panel could not distinguish between the two. Attention has been drawn to some obscurities in the. Here, john explains how to bring the design up to date, adding enhancements such as dccoupled output. Class b amplifier and the classb transistor amplifier. Even using fairly standard 3 way speakers in a large room, surprisingly there is ample power. What strikes me the most is the ability of this amplifier to differentiate between instruments and noises in the sound stage.
Based roughly on the psu designed for the jlh1996 amp, this is a singlerail regulated psu based on an lm1084 or lm338 regulator giving a 5a current limit. John linsley hood amplifier completed page 3 headphone. The quad current dumping amplifier the sandman class s system the technics class aa system. This unique and innovative circuit, subsequently employed commercially in the quad 405 power amplifier, was first disclosed by p. There are piles of forum discussions and sites about this amplifier and its variants on the net, but the main resource is at the classa amplifier site hosted on the always informative elliot sound products web site. Reproduction without prior permission or for financial gain is strictly prohibited. Ive fitted a zobel network on the speaker outputs since the pictures were taken. Aliexpress ebay jl hood 1969 class a amp super best. I built this to evaluate, quality parts used through out. The original version was published in 1969, but thats a little before my time. A zipfile of data on jlhs modular preamplifier design wireless world article, july 1969, contemporary to the simple class a power amp design published in.
I am very pleased with the sonic results of this amplifier. John linsleyhood is best remembered by hifi enthusiasts for his simple class a amplifier, which he developed to provide a goodquality performance comparable to that of the classic williamson amplifier. Some experiments were made to determine the extent to which the circuit performance. The analysis of either ef stage half of the total power amplifier circuit mirrors the presentation of the ef a. Fig 1 shows the basic topology of this circuit which uses an nch phase.
The class ab amplifier runs at a fraction of the class a amplifier current demand, and can be built using simple methods such as matrix board or dead bug style as a project it should be a grade 101. Classa power after two and a half decades, john linsleyhoods classa power amp is still rated among the best. The class ab amplifier cores presented here improve the amplifiers power supply noise insensitivity at high frequencies and increase bandwidth efficiency when compared to the commonly used twostage miller compensated amplifier, enabling the construction of better buffers and more powerefficient and reliable low voltage mixed signal chips. Hybrid power ampl ifiers incorporating both tube and solidstate elements provide options of tone, size and economy. Simple class a amplifier a 10w design giving subjectively better results than class b transistor amplifiers by j. The classa amplifier site primarily dedicated to the john linsley hood classa amplifier designed in 1969 and updated in 1996. It is a truly great amplifier designed by the legendary john linsley hood and i believe it will soon become a legend in itself once people hear it. Valve and transistor audio amplifiers kindle edition by hood, john linsley. Discover over 4 of our best selection of hood 1969 class a amplifier on with topselling hood 1969 class a amplifier brands.
Simple class a ainplifier and modular preamp keith snook. The class ab amplifier runs at a fraction of the class a amplifier current. One channel wasnt working, the driver and o\p transistors had perished. Audio electronics is a unique electronics text in that it focuses on the electronics of audio design and explores the principles and techniques that underly the successful design and usage of analog and digital equipment. Linsleyhood did listening comparisons with his 1969 class a amplifier. John linsley hood, in audio electronics second edition, 1998. Design and compensation of high performance class ab.
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