Amplifier Circuit Diagrams

60 watt amplifier STK4038 schematic circuit diagram

STK4038 is an integrated AF power amplifier that can deliver 60 watts of output power into a 4-ohm load. The internal fixed current circuitry reduces switch ON/OFF clicks. The IC supports the addition of external circuits for the thermal shutdown, pop noise reduction, output short circuit protection, etc.


The 60-watt amplifier shown below is designed based on the datasheet and performs very well. Capacitor C1 is the input DC decoupling capacitor which blocks any DC level present in the audio input and C12 is the input bypass capacitor. R1 is the input resistor.C10 and C8 are the ripple filter capacitors for the positive and negative power supply rails. R9 and R7 are the current limiting resistors for the internal driver stage while C11 and C3 are their corresponding filter capacitors. Resistor R6 feeds back a portion of the output signal to the inverting input (pin2). The gain of the amplifier depends on the value of R6. C9 and R2 form a Zobel network which improves the high-frequency stability of the amplifier.

Application and Uses

  • Reinforcement systems
  • Guitar
  • Electric keyboard
  • Domestic systems
  • Theatrical systems, etc,

Circuit diagram

60 watt amplifier STK4038 schematic circuit diagram

Hardware Components

The following components are required to make 60 Watt Amplifier Circuit

S.No Components Value Qty
1. PCB 1
2. Resistor 4.7 ohms, 100 ohms, 560 ohms, 1K, 56K 1, 2, 1, 1, 2
3. Ceramic Capacitor 0.1uf, 470pf, 100pf, 1000pf 1, 1, 3, 1
4. IC STK4038 1
5. Speaker 4 ohms/ 75watt 1
6. Electrolytic Capacitor 1uf, 4.7uf, 10uf, 100uf 1, 1, 2, 2


  • A good quality PCB improves the performance of the circuit.
  • The maximum supply voltage for STK4038 is +/- 57V DC.
  • K1 is a 4 ohm /75-watt loudspeaker.
  • While using a 4-ohm speaker as the load, the power supply must not exceed +/- 32V DC.
A bypass capacitor is added to an amplifier circuit in order to allow AC signals to bypass the emitter resistor. This effectively removes it from the output gain equation resulting in an increase in the amplifier’s AC gain.
Bypass capacitors are used to maintain low power supply impedance at the point of load. Parasitic resistance and inductance in supply lines mean that the power supply impedance can be quite high. As frequency goes up, the inductive parasitic becomes particularly troublesome.

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