ÿþ<html> <head> <META Name="description" Content="Sound and sound systems - an informal look. A Paul Kemble web page - amplifier."> <META Name="keyword" Content="sound, audio, music, stereo, hi fi, amplifier, power amplifier, power amplifier design, class a, Miloslavskij,"> <LINK media=screen href="" type=text rel=StyleSheet> <STYLE fprolloverstyle>A:hover { COLOR: #b40000 } </STYLE><TITLE>A Paul Kemble web page - Miloslavskij class A amplifier.</TITLE> <body bgcolor="#000000" background="oldpaper.jpg" bgproperties=fixed text="#0033FF" link="#0066CC" vlink="#339966"><FONT face="Verdana, Helvetica, Arial," size=3> <blockquote><br> <b>Miloslavskij class A amplifier</b><p> These designs, using single-ended and/or push-pull layouts with no overall feedback, were adopted as a basis for a 3-way power amplifier (0.5 to 10W) with passive (phase-linear) filters of 6dB/octave. Intended to drive efficient speakers within sound pressure level peaks of 100 to 108dB in rooms with volumes of 30 to 120 cubic metres, comparable to listening to symphonic music somewhere in the centre of the pits at the fortissimo, the upper frequency limit of such amplifiers may be 20MHz or more. This approach, then, recognises the fact that the maximum <i>undistorted</i> sound output of a speaker occurs long before the rated maximum electrical handling specification.<p> Non-linear distortion of the emitter follower depends primarily on the ratio between R3 and the emitter follower's input resistance, as well as on transistor linearity and the local negative feedback of this stage (0.1 to 0.2% max). The smaller the ratio, the lower the distortion. Diodes can be paralleled across the output devices to cope with adverse loads.<br><br> </blockquote><center><img src="milohf.gif" border=0></center><blockquote> Input transistors - Vce(max) of 120-300V, Ic(max) 0.5-1A, fT of 20-50MHz, Pc(max) of 0.6-1.5W and a current gain of 70-140. Output transistors - Vce(max) of 300-500V, Ic(max) 2-5A, Pc(max) of 25-50W and a current gain (Darlington) of 3-5,000. Capacitors in the signal path are chosen to attenuate LF gain.<br><br> </blockquote><center><img src="milohfeq.gif" border=0></center><blockquote> A push-pull version gives a higher output.<br><br> </blockquote><center><img src="milolf.gif" border=0></center><blockquote> Output transistors - Vce(max) of 120-400V, Ic(max) 8-12A, Pc(max) of 50-120W, fT of 3-20MHz and a current gain (Darlington) of 5-10,000 (output device 60-90). For good symmetry of arms R8 H" R9 and ²Tr3 x ²Tr2 H" ²Tr4 x ²Tr5 and preferably ²Tr3 H" ²Tr5. To reduce instability (10 to 20%) of continuous quiescent current with temperature, R8 and R9 can be PTC thermistors. Maximum temperature of transistor junctions must not exceed 70-80&deg;C.<br><br> </blockquote><center><img src="milolfeq.gif" border=0></center><blockquote> A set of three amplifiers, associated filters and controls, regulator and supply could be fitted inside individual speakers thus producing an active system. Alternatively, a separate enclosure could be used. A suitable regulator might be that shown below which, with a 5V operating differential for a 29V supply, can be fed from a 25Vac primary (full-wave rectification to reduce transformer noise). Additional smoothing and decoupling can be placed near the amplifiers.<br><br> </blockquote><center><img src="milreg.gif" border=0></center><blockquote> Other class A designs; <a href="sound3b.html">Linsley Hood</a>, Stan Curtis' <a href="sound7c.html">ETI System A</a> and Jean Hiraga's '<a href="http://www.tcaas.btinternet.co.uk/monster31.htm">Le Monstre</a>'.<p> <center><i><a href="http://htmlgear.lycos.com/feed/control.feed?a=render&i=1&u= paul-kemble">Contact me</a></i><br> especially if you want additional content to this page<br>or if you find any links that don't work. Don't forget<br>to add the page title or URL. Take care!</center><p> <center>Back to <a href="soundindex.html">index</a>, <a href="sound.html">sound</a>, <a href="soundb.html">tips</a> or <a href="index.html">home</a>.</center> </font> </blockquote> </body> </html>
Site hosted by Angelfire.com: Build your free website today!