Symmetrical Audio Class A preamplifier

  
The preamplifier that appears in the figure is a completely symmetrical preamplifier, from the input as the exit and it works in Class A. It does not have somebody innovation, simply it uses good solutions, in order the result is what should. Such proposal is the use transistors matched [Q1, 2], that finds in the same chip with result the thermic and other characteristics are ``perfect``. It can they are replaced by simple transistors as the BC550C and BC560C it`s enough you enter in the fatigue to matched you pairs with similar characteristics. With the TR1 we can if it needs we regulate the Offset voltage in the exit of unit. It can however be suppressed and it`s replaced with two resistances 82 ohm in the place of R6 -7. A point that it should I accent it`s that diodes D1 and D2 it should they are placed very near in transistors Q3 and Q4 respectively, so that they have common thermic behavior. The himself should become also with transistors Q8 - Q10 and Q9 - Q11 respectively.
Symmetrical Audio Class A preamplifier - schematic




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