Passive control of tone. Advantages and ...

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Passive control of tone. Advantages and shortcomings. High-quality sound-reproducing equipment often uses passive controls of tone. In contrast to active controls, which often cause additional distortions in amplified signal, passive controls of tone have simple and rugged design. They however have their own drawbacks.One of them is significant attenuation of signal corresponding to controlled range. But, as depth of tone control in amplification equipment is small, in this case it is not necessary to introduce additional gain cascades in signal path, thus unwanted distortions are avoided.Another of them, though not such a significant drawback, is the need to use variable resistors with dependence of resistance on the angle of engine rotation (Group "B"), providing smooth control.Note that passive regulators require low output resistance of preceding sound source and high input resistance of the following cascade. One example of tone passive control is the classical variant of scheme, developed by British engineer, which became the most common frequency equalizer in amplification equipment.The circuit consists of two links of the first order forming a bridge -- low-frequency R1C1R3C2R2 and high-frequency C3R5C4R6R7. When adjusting tone, equalizer filter changes only slope of amplitude frequency response without changing frequency of inflection.Range of adjustment of amplitude frequency response depends not only on attenuation value but also on selection of the inflection of frequency response.