Preamplifier Circuit Diagram using BC140

Preamplifier Circuit Diagram using BC140 Transistor
Preamplifier Circuit using BC140 Transistor


A preamplifier is an essential component in audio systems as it boosts the weak signals from input devices such as microphones or musical instruments to a level suitable for further processing or amplification. BC140, a popular transistor, has been widely used in preamplifier circuits due to its excellent performance and affordability. In this article, we will explore the preamplifier circuit diagram using the BC140 transistor and discuss its specifications.

BC140 Transistor Specifications:

Before proceeding to the circuit diagram, let us first understand the specifications of the BC140 transistor. The BC140 is an NPN silicon epitaxial bipolar junction transistor that is designed for general-purpose amplifier and switching applications. It features a low collector-emitter saturation voltage and high current gain, making it ideal for audio amplifier circuits.

The key specifications of the BC140 transistor include:

  1. Collector-Emitter Voltage (VCEO): 40 V
  2. Collector-Base Voltage (VCBO): 80 V
  3. Emitter-Base Voltage (VEBO): 5 V
  4. Collector Current (IC): 1 A
  5. Power Dissipation (PD): 625 mW
  6. Transition Frequency (fT): 100 MHz
  7. DC Current Gain (hFE): 40-250

Preamplifier Circuit Diagram using BC140 Transistors

This project can be designed using a few basic components. The circuit diagram of this project is shown below.

Preamplifier Circuit Diagram using BC140
Audio Preamplifier Circuit Diagram using BC140

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Components List of Preamplifier Circuit Diagram BC140

Following is the list of all components used in this project:

  • BC140 Transistor x 2
  • 2.2uF/63v Capacitor x 1
  • 47uF Capacitor x 1
  • 100nF Capacitor x 1
  • 4.7nF Capacitor x 1
  • 1.8nF Capacitor x 1
  • 56k Resister x 2
  • 2.7k Resister x 1
  • 220k Resister x 1
  • 220 Ohms Resister x 1
  • 680 Ohms Resister x 1
  • 330k Resister x 1
  • 1.5k Resister x 1
  • 12k Resister x 1

Explanation of Preamplifier Circuit Diagram BC140

Now, let us proceed to understanding the circuit diagram of a preamplifier using the BC140 transistor. The circuit diagram typically consists of the following components: BC140 transistor, resistors, capacitors, and an audio input device.

The BC140 transistor is connected in a common-emitter configuration, where the audio signal is fed to the base of the transistor through a coupling capacitor. This coupling capacitor blocks the DC component of the input signal, allowing only the AC audio signal to pass through. The input resistor is used to provide bias current to the base of the transistor.

The collector of the BC140 transistor is connected to a power source through a collector resistor, while the emitter is connected to the ground through a resister. The output signal is then taken from the collector terminal through a coupling capacitor to the next stage of amplification.


The BC140 transistor has proven to be an excellent choice for preamplifier circuits due to its favorable specifications and affordability. The circuit diagram discussed in this article demonstrates a simple yet effective configuration utilizing the BC140 transistor for amplifying weak audio signals. With its low saturation voltage, high current gain, and wide frequency response, the BC140 transistor ensures high-quality audio amplification for various applications. By understanding the circuit diagram and specifications, audio enthusiasts and electronics hobbyists can harness the full potential of the BC140 transistor in their preamplifier designs.

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For more project and circuit diagrams, you can go through the Schematics in the main menu where you can find many interesting projects and circuit diagrams like audio amplifier circuits, voltage booster circuitbattery charger circuit and timer circuits etc., which are all beginner circuit projects. Feel free to check them out!

Preamplifier Circuit Diagram using BC140 Transistor
Preamplifier Circuit Diagram using BC140
Preamplifier Circuit Diagram using BC140
Preamplifier Circuit Diagram using BC140

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