Transistors Low Pass filter

If you want a simple low pass filter circuit that will output only low audio frequencies for you, then this is it! The circuit is a simple transistors low pass filter that you can construct and use for your subwoofer project.

This is simple transistors low pass filter circuit which produces low (bass) audio frequencies from the range of 20Hz to 150Hz.
You only need few components to construct this simple circuit. The components can be obtained from your panel junk box. Below are components you will need for this project.
Bipolar Junction Transistor (BJT)

  • One (1) NPN Bipolar Junction Transistor C2383
  • One (1) NPN Bipolar Junction Transistor C2655


  • 22Ω (2)
  • 100Ω (2)
  • 2.2KΩ (1)
  • 3.3KΩ (1)

Polarized Capacitors

  • 10uF (2)
  • 47uF (1)
  • 100uF (1)
  • 220UF (1)

The first stage is base on NPN bipolar junction transistor (BJT) C2383 which cuts off high audio frequencies from the input to low (bass). Then, the second stage which is based on NPN BJT C2655 amplifies these low frequencies generated by the first stage. The low (bass) audio output of the circuit is then fed to the input of the subwoofer power amplifier.

Components Values

Below are  the components values of the circuit

  • C1 and C2=10µF
  • C3=47µF
  • C4=100µF
  • C5=220µF
  • R1=3.3KΩ
  • R2 and R5=100Ω
  • R3 and R6=22Ω
  • R4=2.2KΩ

transistors low pass filter

You may also want to read Low Pass filter 25Hz to 150Hz based on OP Amp IC JRC4588.

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