Amplifier Circuit DiagramsAudio Circuit Diagrams

40 W Output Amplifier Schematic Circuit Diagram

Hybrid Output Module for Amplification:

40 W output amplifier: Despite the availability of numerous hybrid output modules in the market, combining compactness with an affordable price and commendable performance remains a rare feat. However, one such exception is the module from SGS, as employed in the current amplifier. The amplifier’s design is simple, featuring a power operational amplifier (opamp) followed by two output transistors.

Signal Input and Voltage Variations:

The incoming audio signal is directed to the noninverting input of the power opamp IC1 through socket K1 and capacitor C1. Notably, the current supplied to the IC undergoes variations corresponding to the input signal. Consequently, there is an equivalent fluctuating voltage drop observed across resistors R6, R7, R8, and R9, given their placement in the opamp’s supply lines.

40 W output amplifier d.c.schematic diagram

Current-dependent power output:

As long as the current remains below approximately 1 A, the voltage drop across the resistors remains insufficient to activate transistors T1 and T2. In this scenario, the amplifier delivers outputs up to 2 W into a 4-ohm load solely through the power operational amplifier (opamp). However, once the output current surpasses the 1 A threshold, the transistors engage, contributing to the overall power output.

Quiescent Current and Stability:

In instances of a small input signal, there is no quiescent current flowing through the transistors, while the opamp sustains a certain level of quiescent current. This arrangement effectively eliminates crossover issues. Additionally, given the opamp’s provision of thermal compensation, the stability of the operating point is reliably maintained. The permissible supply voltage ranges from 12 V to an absolute maximum of 44 V.

Amplifier Construction and Protection:

The construction of the amplifier on the printed circuit board is expected to be uncomplicated. Both the transistors and the IC need to be securely mounted and insulated onto a heat sink with an approximate thermal resistance of 2 K/W, using an ample amount of heat-conducting paste. Furthermore, it is recommended to incorporate a 3.15 A fuse for protection in the supply line.

40 W output amplifier d.c.schematic diagram

Technical data

  • Supply voltage: 44 V
  • Maximum output: 22 W (8 ohm)
  • (for THD=0.1%) 40 W into 4 (ohm)

Harmonic distortion

  • 1 kHz/8 (ohm)/11 W 0.012%
  • 1 kHz/4 (ohm)/20 W 0.032%
  • 20 kHz/8 (ohm)/11 W 0.074%
  • 20 kHz/4 ohm/20 W 0.2%
  • 1 kHz/8 (ohm)/1 W 0.038%
  • 1 kHz/4 (ohm)/1 W 0.044%
  • QUiescent current is about 38 mA
  • Efficiency 8 (ohm) 62.5%
  • (rnaidrriurri load) 4 (ohm) 64%

40 W output amplifier d.c.schematic diagram,

Parts list:

Resistors:
  • R1-R4 = 100 k (ohm)
  • R5 = 8.2 k (ohm)
  • R6-R9 = 1.4 (ohm) 1%
  • R10 = 1 (ohm)
Capacitors:
  • C1 = 470 nF
  • C2 = 10 pF, 63 V,radial
  • C3 = 4.7 pF, 63 V, radial
  • C4, C5, C7 = 220 nF
  • C6 = 2200 pF, 50 V, radial
  • C8 = 100 pF, 50 V, radial
Semiconductors:
  • D1, D2 = 1N4001
  • T1 = BD712
  • T2 = BD 711
  • Integrated circuits
  • IC = TDA2030
Miscellaneous:
  • K1 = audio socket
  • Heat sink: 2 K W-1
  • Insulating washers, etc. for IC1, Ti, and T2

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