25 Watt amplifier

  
Transistors are used for current sources. Base drive for these transistors is derived from the main power supply VA, so that their collector current is proportional to the rail voltage. This feature holds the voltage on the cliff-amp collectors close to VA/2. The sensitivity of Iq to VA is about 3.4 mA/volt when VB is held constant; the sensitivity of Iq to VB is -15 mA/volt when VA is held constant. In a practical amplifier with a non-regulated supply, variations in power output will cause fluctuations in VA, but will not affect VB; therefore, having Iq increase slightly with power output will tend to compensate for the 3.4 mA/volt IqVa sensitivity.
25 Watt amplifier  - schematic

In the case of line voltage variations, since VA is about five times VB, the sensitivities tend to cancel, leaving a net sensitivity of about 2 mA/volt.




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