compact power amplifier
This realization prompted the presentcompact power amplifier whose quality and layout match those of thepreamplifier. It offers medium power output, is not overly complex andhas a very high slew rate.
The introduction gives a good idea ofthe power amplifier described in thisarticle.The term ‘compact’ refers to boththe power output and the dimensionsof the amplifier. Of course, compactnessis a relative term, because theamplifier contains no fewer than 19transistors. Over the years, compactnesshas taken on a different meaningthan, say, ten years ago. Then, a compactamplifier was understood to containnot more than eight to ten transistors;today this figure is nearer totwenty-five. After all, as everybodynow realizes only too well, qualityalways has its price.As far as output power is concerned,the present amplifier is definitelyintended for normal domesticuse.
It produces some 50 watts into 8 or 85 watts into 4 , which is morethan ample for its intended use. Evenat relatively high volume, a domesticpower amplifier seldom provides morethan 1–2 power output. To highvolumefreaks it may soundodd, but most loudspeakersproduce a sound pressureof about 90 dB at a distance of 1 metrefor an input of only 1–2 watts—enough to make the neighbours rushfor the telephone.It is clear, therefore, that the presentamplifier has more than ample reserveto reproduce even the highest peaks ina piece of music without any discernibledistortion.A further benefit of the circuit is theuse of such a relatively high quiescentcurrent that with power outputs up to2.5 W the amplifier operates in Class A,which enhances the overall quality ofthe reproduced sound.