Design of a 50w power amplifier driven by an active 4-way cross-over network and a pre-amplifier

Abstract

Most speaker boxes have an electronic circuit inside them called a crossover. Its job is to split the sound into frequency ranges; it sends the low frequency sounds to the woofer, and the high frequency sounds to the tweeter. This is important because each of the loudspeakers is built to produce certain frequency ranges, and they don ’ t sound very good outside of their proper range. Most speaker boxes come with passive crossovers built in. The crossovers are made up of some inductors and capacitors that filt er the low frequencies from the highs. But passive crossovers have a number of very significant drawbacks. The biggest problem with passive crossovers is that they significantly degrade the quality of the signals that pass through them by introducing disto rtion. Music systems of today have separate speakers (woofer, midrange and tweeter) connected to the output of amplifiers. This project entails the design of a 50W power amplifier driven by an active 4 - way cross - over network. An active crossover, is buil t from the highest quality operational amplifiers (op - amps) and the filter functions are applied to the millivolt level, high impedance, line - level preamp input instead of the low impedance, high voltage level amplifier output. The active filters are to se parate the sounds into 4 - band i.e. the Bass - band, midrange - 1, midrange - 2 and tweeter - band. The biggest advantage of active crossovers is the sound quality. A vanishingly small amount of noise and distortion is introduced in the op - amp filter circuits, on the order of 0.00005% total harmonic distortion.