This is a symmetrical amplification unit circuit, more composed, modified by a construction which was proposed some years ago by Lisley Hood. The most important reason is to get the right transistor FET at differential amplifier at input. In spite of all this it is a circuit which provides, current mirror stage of both sides, with the result of lessening the overall negative feedback. The exactness of the matches of the transistors - resistances are determined and for the details. The trimmer TR1, make less the offset voltage at input.

Circuit diagramHow to build Symmetrical Preamplifier Class A - circuit diagramPart List
  • R1= 47Kohms
  • R2-4= 220 ohms
  • R3-5= 100 ohms
  • R6-7= 470 ohms
  • R8-9= 220 ohms
  • R10= 5.6 Kohms
  • R11= 1 Kohms
  • R12= 10 Kohms
  • R13-14= 820 ohms
  • R15= 47 ohms
  • TR1= 1 ohms trimmer
  • C1= 4.7uF 100V MKT
  • C2-3= 100nF 63V MKT
  • Q1-2= BC214
  • Q9= BC214
  • Q10= BC212
  • Q11= BC182
  • Q7-8= BC184
  • Q12= BC184
  • Q3-4= 2N5457
  • Q5-6= 2N5460

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