Transistor equalizer circuit diagram

Here is the transistor graphic equalizer circuit.

Why should make this circuit?

Transistor equalizer circuit diagram

We use it for controlling the audio frequency in some kinds of audio frequency responses that are not flat.

Which we cannot use a normal tone control circuit. Because it has a too wide bandwidth.

We need to use a good equalizer circuit that can respond to narrow bandwidth down. And, divide into frequency bands increased to 5 channels or more.

It can control specific actions required by frequency bands.

If you want to learn a basic equalizer. I am going to show you a simple circuit like the transistor tone control circuit.

Read also: TOP 7 Tone control circuit, Low noise

What is more?

How it works

Look at the circuit, without ICs.  So, low noise and easy.

Transistor equalizer circuit diagram

Transistors Graphic equalizer circuit

This equalizer circuit can be adjusted the frequency to 5 channels 60 Hz, 100 Hz, 1 kHz, 3 kHz, and 12 kHz.

And, this project consists of stereos, right and left channels. It is the same. So, we will learn only the right channel (Mono).

In-circuit is Mono. If you want stereo. Just add Mono another one only.

I want you to understand easier. Seeing the block diagram may you more.

block diagram of transistor graphic equalizer

It looks like a preamplifier with a tone control that adds many bandpass filter ranges.

Read next: 4 Preamplifier circuits using transistors

When we enter a signal to the input. Then, C1 passes a signal to coupling through pin1  each potentiometer (VR1-VR5).

If we adjust VR5 to a higher level in the middle of a potentiometer.

This signal will come to a high and low-frequency filter of each band. They include the R and C networks.

Next, the signal that through each band be combined together.

Then, C10-capacitor passes the signal to coupling to a base of Q1 and Q2.


Both transistors are common emitter amplifiers.

The higher signal goes out of a collector of Q1. It is out of phase with the input.

Then, the highest signal or the output signal comes out of the emitter of Q2 via C13.

And, some signals will be feedback through R12 to each leg 3 of the potentiometer (VR1 to VR5).

When we adjust them to this point.  A feedback signal will refute with an input. So, this is a cut-off point.

Recommended: Learn transistor circuit works here

How to builds this project

First, find the components of this project. See the parts lists below.

Parts you will need

0.25W Resistors, tolerance: 5%

  • R1, R2, R3, R4: 22K
  • R5, R6, R7, R8, R9: 33K
  • R10: 1.2M
  • R11: 220K
  • R12: 1K
  • R13: 5.6K
  • R14: 470 ohms
  • VR1-VR5: 50K(B) stereo potentiometer


  • C1,C10,C13: 1uF 50V Electrolytic
  • C2: 0.047uF 50V Mylar
  • C3, C4: 0.022uF 50V Mylar
  • C5,C6: 0.0047uF 50V Mylar
  • C7, C8: 0.0015uF 50V Mylar
  • C9: 390pF 50V Ceramic
  • C11: 39pF 50V Ceramic
  • C12: 100pF 50V Ceramic


  • Q1: BC549 or BC548 Transistors
  • Q2: BC558 or BC557 Transistors


  • PCB, Wrres, etc.

Read also: Low Voltage Preamplifier Circuit with Tone Control using transistors

You can see the PCB layout in Figure 2 as Mono.

PCB layout graphic equalizer transistor

Single-sided PCB layout

And can see the components layout in Figure 3.

Components layout transistor equalizer circuit

The Component layout of this project in mono.

The wiring for circuit wiring and various parts to check the polarity of the electrolytic capacitors and Diodes and transistors correctly.

Though so easy, you need to solder it with neat.

Note: The PCB layout scale is 200/inch. You can print on the laser printer to make PCB easily.

See Connecting the graphic equalizer to the audio amplifier system below.

Connecting the graphic equalizer to the audio amplifier system

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9 thoughts on “Transistor equalizer circuit diagram”

    • Hi Kelly,
      I am sorry. It makes you wasted a lot of time.
      But I am confident that You develop yourself.

      You are who “Look for the opportunity that is hidden in every adversity”.

      I was embarrassed. Thanks a lot.

      Please recheck it circuit again and
      Share your knowledge and experiences.


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