Amplifier Circuit Diagrams

60 watt amplifier STK4038 schematic circuit diagram

The 60-watt amplifier, STK4038, is an integrated AF power amplifier with the capability to produce an impressive 60 watts of output power when connected to a 4-ohm load. What sets it apart is its internal fixed current circuitry, effectively mitigating undesirable switch ON/OFF clicks.

Furthermore, this IC is designed to accommodate the incorporation of external circuits to enhance its functionality, such as thermal shutdown mechanisms, reduction of pop noise, and protection against output short circuits, among other features.


The amplifier depicted below, designed in accordance with the datasheet, exhibits exceptional performance. Capacitor C1 serves as the input DC decoupling component, effectively isolating any DC level that may be present in the audio input. Additionally, C12 functions as the input bypass capacitor. R1 plays the role of the input resistor.

C10 and C8 serve as the ripple filter capacitors for the positive and negative power supply rails, ensuring stable power delivery. R9 and R7 act as current limiting resistors for the internal driver stage, and they are accompanied by C11 and C3, which function as corresponding filter capacitors.

Notably, resistor R6 provides feedback by channeling a portion of the output signal to the inverting input (pin 2). The amplifier’s gain depends on the value of R6.

To enhance high-frequency stability, C9 and R2 form a Zobel network, a crucial addition to the circuit design.

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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