Miniature amplifier - with active tone control

H There are many ICs available today that contain all the circuitry required for various versions of power output stages. The IC presented here goes even further than that. It can be used as a complete amplifier. Obviously it is not super hi-fi but for a second (or third) amplifier it is quite good enough. The IC LM 389 was used in the Summer Circuits issue last year. In that case it formed the basis for a small siren. The resemblance between a siren and an amplifier is quite obvious and the natural progression is published here. The IC contains a small power output stage and three further transistors on the same chip. This means that no miniature amplifier . with active tone control further active components are required for the amplifier. The gain of the output stage is simply set by means of a capacitor and a resistor. In the cir- cuit diagram the gain is set at 20x (26 dB) which means that pins 4 and 12 are simply left floating. If a 10 pF capacitor is connected between the...