70/90 watt amplifier - a class AB design for 4 Q or 8 Q loads

a class AB design for 4 Q or 8 Q loads This is an amplifier with a very simple layout that none the less pro- duces quite a high power. Power isn"t everything, however, (no matter what some politicians think) so it is backed up in this case by the other specifications, which are quite good. A symmetrical supply was chosen in order to avoid the problem of having to use an electrolytic capacitor at the output. Consequently a differential amplifier is used at the input. The in- put signal is fed to the base of tran- sistor T1 and feedback is taken from the base of T2. The current through the differential stage is kept at a con- stant 1 mA by the action of current source T3. The amplified input signal is taken from the collector of T1 to darlington T4/T8, which, in com- bination with current source T5, forms the class A driver stage for the power transistors. The current through the driver stage is quite small (about 7 mA) because T6 and T9 are power darlingtons. The class AB quiescen...