Band-independent tone adjustment circuit

The main component of this circuit is the active RC filter as shown in the figure. It is a unique equalization circuit used to correct the frequency characteristics of audio equipment. With exquisite materials and workmanship, it has a stronger ability to enhance treble and bass than ordinary tone circuits.

The entire circuit is composed of three completely identical and independent (non-interfering) links connected in series. The only difference between the three circuits is the parameters of the bridge components R4, C4, c5, RP2A, RP2B, and R5 in the circuit. The resistance values ​​of the three frequency bands are shown in the attached figure, and the capacitance data are shown in the attached table.

The tuning frequency within the frequency range listed in the attached table is determined by the coaxial potentiometers RP2A and RP2B: the level boost or attenuation (±14dB) required by the circuit is adjusted by potentiometer RP1.

In actual use, when the sound is raised and lowered in sections, it feels like only the frequency is changing, not the sound quality.

The input impedance of this circuit is 47kΩ (the resistance value of R1 can be changed according to the requirements of the actual interface). The operational amplifier in the circuit is NE5532. Other dual operational amplifiers have also been used. However, NE5532 has good adaptability to low power supply voltage, delicate and soft sound, mellow and warm bass, and extraordinary treble resolution, which meets the characteristics of this circuit and is the preferred IC for making this circuit.

The quality of the power supply should not be underestimated. In situations where high sound quality is required, more attention should be paid to the power supply. A servo-regulated power supply and a C-type transformer can be used for power supply.