ETI-477-pwr-维修说明书手册含电器原理图1

Project 477MOSFET power amplifierPart 1.Employing recently released Hitachi MOSFETs,this power amplifier features a 'nocompromise'design,is rated to deliver 150 W RMS maximum and features extremely lowharmonic,transient and intermodulation distortion.As the circuit techniques and designproblems will be unfamiliar to many readers,a thorough discussion of the theory andproblems is included.David TilbrookTHE ENORMOUS SUCCESS of theseries 4000/1 four-way loudspeaker hassurprised even us.They were originallySPECIFICATIONSintended to be the'flagship'ofa range ofloudspeakers and quite frankly we ex-pected the biggest demand to be for theINPUT OPower outputcheaper loudspeakers further down the100 W RMS into 8 ohmsrange.This has proved not to be the case(±55 V supply)as sales of four-way kits continue to rise.It is evident that there is a big demandFrequency responsefor the higher quality audio projects.We8 Hz to 20 kHz,+0-0.4 dBrecognised this demand and eightFigure 1.Simplified circuit of a blpolar output2.8 Hz to 65 kHz,+0-3 dBmonths ago began the development ofstage.NOTE:These figures are determinedthe Series 5000 power amp and preamp.Q1 is turned on by a positive-goingsolely by passive filters.The objective was to design an amplifierfor home construction of the highestsignal voltage the impedance betweenInput sensitivitypossible quality.The cost of the projectthe output and the positive supplydecreases and the output approaches1 V RMS for 100W outputwas a secondary consideration,although in real terms the cost saving in+V.Similarily,if Q2 is turned on theimpedance between the output and theHumdoing it yourself"is considerable.negative supply rail decreases and the-100 dB below full output(flat)discussionoutput approaches-V.When eitheroutput transistor is turned fully on,theNoiseoutput voltage will be equal to the-116 dB below full output(flat,20 kHz bandwidth)Defining the problemsupply voltage minus whatever voltagedrop occurs across the output tran-Of all the stages in the amplifier thesistors.Any signal peak that exceeds2nd harmonic distortionit isoutput stage is subjected to the worstthis maximum output voltage will be<0.001%at1kHzmeasoperating conditions:.varyingloadamplitude limited or clipped(see Figure(0.0007%on prototypes)Thisimpedance,heating due to the large2).It is possible to compress signalat 100 W output using apowe:power levels necessary to drive loud-peaks that may otherwise±56 V supply rated at4Acausetinuospeakers,and the occasional shortclipping,but inevitably,thecontinuous.non-indic;circuit produced by the carelesslinearity still occurs.The large supply<0.003%at 10 kHz and 100 Wcapabconnection of loudspeaker cables orvoltages associated with high poweredrecorperhaps even loudspeaker failure.amplifiers help reduce this problem and3rd harmonic distortionpeaksThe output stage is also the site ofare one of the reasons that high power<0.0003%for all frequenciesabovethree distinct sources of gross non-amps almost always sound better than