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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 preamplifier with tone controls project

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

the schematic circuit diagram
Figure 1 the schematic circuit diagram

How it works

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 the class A. To protect a crossover distortion. The C3 capacitor to cut high-frequency interference. The output of 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 adjust 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 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

Parts you will need

1% 0.25W Resistors (metal film types)
R9,R17_100 Ω
R11,R13_100 Ωs 0.5W
R18, R19_10K

C1_470 pF 50V metalized polypropylene capacitors
C2,C20,C22_0.1μF 63V MKT (Metallized Polyester Film Capacitor)
C3_100 pF 50V metalized polypropylene capacitors
C4_10μF 100V MKT (Metallized Polyester Film Capacitor)
C5_0.0015μF 63V MKT (Metallized Polyester Film Capacitor)
C6_0.015μF 63V MKT (Metallized Polyester Film Capacitor)
C7_0.047μF 63V MKT (Metallized Polyester Film Capacitor)
C8_0.47μF 63V MKT (Metallized Polyester Film Capacitor)
C9,C10_220μF 16V Electrolytic capacitors
C11,C13,C15,C16_0.01μF 63V MKT (Metallized Polyester Film Capacitor)
C12,C14_220μF 25V Electrolytic capacitors
C17,C18_2200μF 25V Electrolytic capacitors
C19,C20_100μF 25V Electrolytic capacitors

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 ICs
IC2_____________LM7918_____18V negative DC regulators ICs
D1,D3___________Positive full wave diodes
D2,D4___________Negative full wave diodes

Others parts
transformers, PCB, and more.

The PCB layouts
Figure 2 The PCB layouts

The components layouts
Figure 3 The components layouts

This projects may not be suitable for a beginner. You should have expertise in electronic medium.

This project worked. Please watch in this video.

Thanks, Jerivall good job!

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This Post Has 18 Comments

  1. Excellent.

  2. i need transistorized diagram of kvt audio booster amplipier

  3. is this work? pls. reply?

  4. is this work? pls. reply cuz i like this if it’s work.

  5. I know you can explain it better

  6. hello, i have built some of your projects but now I would like to buy some of the pc boards that go with the projects, how can I buy the pcb’s?

  7. can you send the simulation and pcb layout files?

  8. Hello author! Can this be powered by +-15V instead of 18V? Has anyone built this circuit that can confirm if it works?

  9. Here output are connected speaker??????

  10. hi
    Hi Fi audio tone control circuit using low noise transistors i see this project and i thing its a good one. i want to know how can i buy this pcb and all components and how much its cost.

  11. Please make an audio amplifier with image and video

  12. Please make a simple audio amplifier board with image and video please

  13. The preamplifier has a lot of noise and I do not know how to get rid of it

  14. Hi
    I wanna build this tone control so can you, please, give me the layout file for pcb ?
    Thank you !

  15. The pre amp is made with a different pcb made by me. It produces a constant hum even at volume control minimum. This hum is constant at all volume control position. The pcb is redisned and made by including a 4.7k and 220 mfd decoupling capacitor in both +ve and –ve power supply. This is included only for Q1, Q2, Q3 and for Q4. The hum remains same. when I removed the input to Q5 and Q6 ( by cutting the track to the base) the hum goes off. The amplifier is silent. That means the hum is produced in input stage or in the feed back stage. Anybody experienced the same hum. Any remedy.

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