This circuit is Classic Classic amplifier OTL circuit at change quality adaptation. it is model OTL 20Watt hot popular in miss until contain now. Because of there is completed property more than other circuit. In about the popularity in the sound most , compare with reserve the electric power watt be equal group this circuit has will a voice loud very more. Besides still have tall durability convenient for the work PA actually. From circuit picture use transistor all high-quality. Begin from Differential a pair is first use transistor number BC109, AC176, A128. The part driver circuit Q1 use BC109. The part numbers Drive transistor back pair use BC109, AC176 numbers. For the OTL transistor output use the number , AC176, A128. Then make have the drive has about 20 Watt at load 8 ohm.