Hi Fi audio tone control circuit using low noise transistors

The Hi Fi audio tone control circuit features tune smooth bass, and treble is not spicy, with a very low distortion. Please below : more Features
-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

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 ohms
R11,R13______________100 ohms 0.5W
R14__________________330 ohms
R18, R19_____________10K

C1_______________470 pF 50V metalized polypropylene capacitors
C2,C20,C22________0.1uF 63V MKT (Metallized Polyester Film Capacitor)
C3________________100 pF 50V metalized polypropylene capacitors
C4________________10uF 100V MKT (Metallized Polyester Film Capacitor)
C5________________0.0015uF 63V MKT (Metallized Polyester Film Capacitor)
C6________________0.015uF 63V MKT (Metallized Polyester Film Capacitor)
C7________________0.047uF 63V MKT (Metallized Polyester Film Capacitor)
C8________________0.47uF 63V MKT (Metallized Polyester Film Capacitor)
C9,C10____________220uF 16V Electrolytic capacitors
C11,C13,C15,C16___0.01uF 63V MKT (Metallized Polyester Film Capacitor)
C12,C14____________220uF 25V Electrolytic capacitors
C17,C18____________2200uF 25V Electrolytic capacitors
C19,C20____________100uF 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.


  1. Max March 18, 2017
  2. Anand March 25, 2017
  3. Anand March 25, 2017
  4. Jerivall June 6, 2017

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