Hi Fi audio tone control circuit using low noise transistors

If you are looking for a Hi-Fi audio tone control circuit. This may be the best choice for you. Because it uses all low noise transistors.

The circuit is designed to adjust a smooth bass, and treble is soft sound with very low distortion.

Hi Fi audio tone control circuit using low noise transistors
Hi Fi audio tone control circuit using low noise transistors

Special feature

  • Use low noise transistors
  • Frequency response range: 20Hz-20KHz
  • Total Harmonic Distortion Noise 0.001% at frequencies 20Hz-20KHz
  • Maximum output voltage 14Vrms at frequencies 20Hz-20KHz
  • Input sensitivity is 50mV
  • The increase / decrease rate of bass : +/- 17dB at 20 Hz
  • The increase / decrease rate of treble : +/- 17dB at 20KHz

Recommend: Active Bass Boost circuit using IC-741

How it works

See the audio tone control circuit below.

Hifi Preamplifier with tone control using low noise
Hi-Fi Preamplifier with tone control using low noise

The transistors Q1, Q2, and Q3, Q4 are connected together as the differential amplifier.

Then the output signal of lead C of Q1 and Q3, Next, sent to Q5, Q6, and Q7, Q8, amplifier set.

The bias of Q5, Q6, and Q7, Q8 will be set in class A. To protect a crossover distortion. The C3 capacitor to cut high-frequency interference.

The output of the circuit is in lead C of Q8 through C4 and R14. For, C4 in the circuit using 10uF 100V, we may use 6.8uF 250V instead, No effect on sound quality at lead C of Q6.

The sound output is sent through R, C circuit to adjust the sound through the middle pin of VR3 and VR4 passed through R9 to R17 and R18 lead B of Q4.

Which is negative feedback if VR raised above, the negative feedback signal which is a lot, to make the bass and treble down. If at the center of the output signal will out of directly.

Without adjusting bass and treble. If VR adjusted downward if the feedback is less. the bass-treble will up.

This is the feedback tone control circuit that someone may need more treble was achieved by reducing the R16 from 1K to 100 ohms.

The power supply are positive and negative, by use both 18V DC regulators ICs as LM7818 and LM7918 to apply voltage at +18V and -18V

18V Dual Regulator circuit diagram using IC7818 and IC7918
18V Dual Regulator circuit diagram using IC7818 and IC7918

Read Also: Mini Stereo tone control circuit using IC TDA1524A

Parts you will need

1% 0.25W Resistors (Metal film types)
R1, R16, R20: 1K
R2, R3, R15: 4.7K
R4: 1M
R5, R8: 15K
R6, R7: 75K
R9, R17: 100 Ω
R10, R12: 43K
R11, R13: 100 Ωs 0.5W
R14: 330Ω
R18, R19: 10K

Metalized Polypropylene Capacitors (MKT)
C1: 470 pF 50V
C2, C20, C22: 0.1μF 63V
C3: 100 pF 50V
C4: 10μF 100V
C5: 0.0015μF 63V
C6: 0.015μF 63V
C7: 0.047μF 63V
C8: 0.47μF 63V
C9, C10: 220μF 16V
C11, C13, C15, C16: 0.01μF 63V

Electrolytic Capacitors
C12, C14: 220μF 25V
C17, C18: 2200μF 25V
C19, C20: 100μF 25V

VR1: Volume 100K-MN types
VR2: Dual volume 100K-A types with center trap
VR3, VR4: Dual volume 100K-B types

Q1, Q2, Q7, Q8: BC550, low noise transistors
Q3, Q4, Q5, Q6: BC560, Low noise transistors
IC1: LM7818, 18V positive DC regulators IC
IC2: LM7918, 18V negative DC regulators IC
D1, D3: Positive full-wave diodes
D2, D4: Negative full-wave diodes


You may not buy these diodes. But you can modify them. Look at below:

full wave rectifier diodes

Others parts
transformers, PCB, and more.

The PCB layouts

Figure 2 The PCB layouts

The components layouts

Figure 3 The components layouts

Hi Fi preamplifier with tone controls project


This project may not be suitable for a beginner. You should have expertise in medium electronics .

This project worked. Please watch this video.

Make: HI-Fi audio tone control project

Thanks, Jerivall good job!

Check out these related articles, too:


I always try to make Electronics Learning Easy.

Apichet Garaipoom

I love the electronic circuits. I will collect a lot of circuit electronics to teach my son and are useful for everyone.
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