Power Amlifier 40W Class A


This is an audio power amplifier, with its final stage giving 40 W/8 Ω at Class A. The power transistors, are always ON , allowing a very high current to flow. There are plus and minus in that : high power consumption, high emitted temperature e.t.c, but also ideal working area for the transistors, much better audio characteristics, low distortion. This final amplifier is very simple in designing. It requires some experience in assembling. In the prime design, Nelson Pass used Darligton transistors for the output stage. These transistors are produced by the American company Lambda. It is hard to be found , but you may try. I have changed them with most commonly used (see list). Generally the make should be assembled in a big case with powerful power supply and big heatsink . More about this amplifier and Class A theory, in N. Pass site. Source: The Audio Amateur 4/78

Circuit diagram

Circuit diagram

Part List

  • R1=10ohm
  • R2-16 =2.2Kohm
  • R3-9= 10Kohm
  • R4-6 =330ohm
  • R5-11-12 =470ohm
  • R7=680ohm
  • R8-13= 100ohm
  • R10= 4.7Kohm
  • R14-15=68ohm
  • R17-18 =0.68ohm / 5W 5%
  • R19-20 =0.68ohm /5W 5%
  • R21 =10ohm /1W 5%
  • C1=330 pF 100V 5%
  • C2-4=220 uF 16V
  • C3=39 pF 100V 5%
  • C5-6=100nF 100V
  • C8-9=100nF 100V
  • C7-10=220 uF 63V
  • D1-2-3=1N4148
  • TR1=1k2 Trimmer
  • T1-2=MPSL01
  • T3=2N5248 - J204 - BF245C
  • T4-5=MPSL01
  • T6=MPSL01
  • T7=MPSL51
  • T8-9=PMD16K100 Lambda 2N6284 RCA
  • T10-11=PMD17K100 Lambda 2N6287 RCA

ALL Resistors is 1% metal film