Low distortion and high thermal stability in transistor audio power amplifier

Two paramount objectives in the design of a high-quality transistor audio power amplifier are attaining good linearity and ensuring good thermal stability. Conflicts frequently arise in realizing these objectives in that steps taken to achieve one tend to worsen the other. This paper examines these two subjects to determine the essential conditions which must be fulfilled in order for the objectives to be met. As a result of this examination the requisite conditions are found and several useful circuit techniques are developed. These techniques provide excellent thermal stability and at the same time permit attaining good linearity with reasonable amounts of negative feedback. Experimental results are given which confirm the validity of the principles and the value of the techniques.