Five-band active tone control. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Tone, volume controls

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A distinctive feature of the device is a low level of intrinsic noise and non-linear distortion, as well as a small frequency response unevenness when the band-pass controls are set to the same position and its “smoothness” when the controls are set to different positions (the frequency response does not have a “waviness” inherent in the frequency response of most similar devices).

The main parameters:

• Nominal frequency range, Hz, with a decrease in the frequency response at the edges - 3 dB and an input voltage of 1V (sliders of all regulators in the middle position) ...... 8 ... 30
• Input voltage, V: nominal ....... 1
• maximum) ...... 2,9
• Harmonic coefficient,%, at an input voltage of 1 V (regulator sliders in the middle position) at frequencies of 100, 1000, 10 Hz) ...... 000
• Tone control limits at frequencies 50, 200, 800, 3200 and 12 800 Hz)......±12
• Relative noise level (at an input voltage of 1 V), dB ....... - 80

The device consists of an input emitter follower on the transistor V1, five active bandpass filters. Z1-Z5 (the diagram shows one of them - Z1) and a two-stage amplifier on transistors V2, V3.

The timbre is regulated by variable resistors 1R2-5R2. Fixed resistors 1R1-5R1, 1R3-5R3 connected in series with them limit the regulation limits to -12 dB. By reducing their resistances, the regulation limits can be extended up to ±25 dB.

Active filter amplifiers (1V1 - 5V1, 1V2 - 5V2) are identical in circuit and differ from one another only in the values ​​of the capacitors 1C1 - 5C1, 1C2 - 5C2 of the frequency-setting circuits. OOS voltages are removed from part of the emitter load of transistors 1V2 - 5V2 and fed into the base circuits of transistors 1V1-5V1. The intervals between active filter tuning frequencies are chosen equal to two octaves. The filter transfer coefficient at tuning frequencies is 6, the quality factor is 1.

The signals from the outputs of active filters are fed to the input of a two-stage amplifier through resistors 1R9-5R9, the resistances of which also determine the mode of operation of transistors V2, V3 in direct current. Correction circuit R6C5 increases the stability of the amplifier at high frequencies. To power the stereo version of the device, a stabilized source is required that provides a voltage of 40 V at a current of 50 ... 15 mA.

The regulator can use any high-frequency silicon transistors of the appropriate structure with a permissible voltage between the emitter and collector of at least 15 V and a static current transfer coefficient h21e of at least 200 (1V1 - 5V1) and 70 (the rest). The permissible deviation from the capacitance values ​​\u1b\u1bof the capacitors 5C1 - 1C2, 5C2 - 4C5 and the resistances of the resistors lR4 - 1R5, 5R5 - 10R1 indicated on the diagram should not exceed ± 2%. Variable resistors 5R2 - XNUMXRXNUMX must be group A.

The number of control bands can be increased by reducing the intervals between filter tuning frequencies to one or one third of an octave. The values ​​of the quality factor and the parameters of the resistors of the frequency-setting circuits for these cases are given in the table.

Permissible deviation of the parameters of the elements of the frequency-setting circuits of the octave (ten-band) regulator is ± 10%, the one-third octave ± 5%. The regulator does not require adjustment.

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