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.
- 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
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 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
Parts you will need
1% 0.25W Resistors (Metal film types)
R1, R16, R20: 1K
R2, R3, R15: 4.7K
R5, R8: 15K
R6, R7: 75K
R9, R17: 100 Ω
R10, R12: 43K
R11, R13: 100 Ωs 0.5W
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
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
transformers, PCB, and more.
Figure 2 The PCB 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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