A circuit for producing extraordinary tones

In audio circuits, general tone circuits have simple structures and are not ideal for correcting frequency characteristics. Graphic equalizers can correct frequency characteristics in sections, but they have the disadvantages of complex circuit structures and are prone to contaminating sound quality.

After exploration, comparison, debugging and audition, the circuit was improved again and again, and a tone main circuit with simple circuit, easy debugging and extraordinary sound was produced. The circuit is shown in the attached figure. Its characteristics are between the general tone circuit and the equalizer, and it has the advantages of both. The reason why it can do this is that the cut-off frequency of the low and high ends of the frequency are adjusted independently. The range of 20Hz to 500Hz at the low end is adjusted by potentiometer W1. The range of 5kHz to 20kHz at the high end is adjusted by potentiometer W2. Potentiometers W3 and W4 are used to adjust the rise and fall of the frequency characteristic curve. Since these two potentiometers are connected to the inverting input terminals of op amps IC1 and IC2, the mutual influence of these adjustments can be completely eliminated without any additional measures.

The circuit as a whole does not invert the signal and will not cause changes in the sound field. Its transmission coefficient is equal to 1 in the intermediate frequency part, and its output impedance is low. The input impedance (Rin = 10kΩ) is independent of frequency.

The regulation performance depends on the resistance values ​​of resistors RA and RB. According to my test, when RA=―RB-4.7kΩ, the regulation performance is ±l0dB. In order to change the regulation performance, the resistance values ​​of RA and RB must be increased proportionally.