Multi-band filterless equalizer. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Multi-band filterless equalizer. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Audio equipment

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To adjust the frequency response of amplifiers, multiband active or passive RC or LC filters are usually used. Such devices contain a large number of elements that require individual adjustment and cannot be used in compact equipment.

A diagram of a simple filterless equalizer with 12 frequency channels is shown in the figure. The shaper of rectangular control pulses is made on the comparator DA1. From the output of the comparator, the signal is fed to the "frequency / voltage" converter, made on the basis of elements C3, C4, VD1, VD2, R9. The signal, the voltage of which is proportional to the frequency of the input signal, is fed to the control input of the linear LED scale (pin 17) of the DA2 chip. The signals taken from the DA2 chip through the inverters DD1, DD2 control the inclusion of 12 analog switches made on the DA3...DA5 chips. The output signal of the equalizer is formed by summing the analog signals from all 12 channels with separate regulation of the frequency components by potentiometers R23...R34.

Fig.1 (click to enlarge)

The operating threshold of the comparator DA1 is set by the potentiometer R4. The maximum turn-on sensitivity of the comparator can be set to 10 mV. To ensure a smooth setting of the threshold, it is desirable to make the potentiometer R4 composite (of two connected in series and providing coarse and smooth adjustment). The HL1 LED indicates the presence of an over-threshold signal at the input of the device. Linear conversion of the input signal frequency into voltage occurs in the frequency band from 2.5 to 3...930 kHz. The conversion slope is 2,3 Hz/V. In the frequency band of 3 ... 1,77 kHz and above, the conversion slope smoothly increases to XNUMX kHz / V.

Potentiometer R7 sets the upper limit of the control voltage (from 1 to 6 V), potentiometer R10 sets the lower limit (from 0 to 5 V). The Zener diode VD4 protects the control inputs of the DA2 chip from surges, while stabilizing the control voltage. Diodes VD5, VD6 automatically provide a minimum difference between the upper and lower levels of the control voltages at pins 3 and 16 of the DA2 chip at 1 V. Diode VD3 protects the LED scale control circuit from overvoltage.

Thus, if an over-threshold analog (or digital) signal arrives at the input of the device, then as its frequency increases, the indication channels will switch smoothly in turn (LEDs HL2 ... HL13).

At the same time, the control signals from the outputs of the DA2 microcircuit through the CMOS inverters DD1, DD2 will go to the control inputs of the analog "MOS switches (DA3 ... DA5 microcircuits). In turn, depending on the input signal frequency, these microcircuits control a resistive divider that forms final output signal.

The bandwidth of each of the channels, when installed on the control inputs 3 and 16 of the DA2 microcircuit, the maximum and minimum levels 6 and O V, respectively, will be 400 Hz for the first six channels, and 760 Hz for the rest. Thus, the first channel will pass signals with frequencies below 400 Hz, the second - in the band 400 ... 800 Hz, and the last, 12th channel will pass frequencies above 6 kHz. By adjusting the potentiometers R7 and R10, you can smoothly change the width and boundaries of the frequency channels.

Potentiometers R23...R34, which regulate the weight values of the frequency components at the output of the equalizer, are set to the initial position so that their resistance is 100 kOhm. Thus, the limits for adjusting the rise/fall of the signal level for each channel will be 10 times (20 dB). Potentiometers R23...R34 can be replaced by a set of switched resistances, which will allow you to linearize the tone control scale. The resistance of public keys DA3...DA5 is 50...80 Ohm. To reduce the influence of switching transients on the quality of the output signal, these switches can be shunted by corrective RC circuits.

The number of frequency channels can be doubled by typical cascading of DA2 chips. The frequency/voltage conversion range can be controlled by changing the capacitance of the capacitor C3. The UAA180 chip can be replaced with a complete analogue - A277D, K1003PP1, etc. LEDs HL2 ... HL13 dynamically indicate the number of the active control channel. These elements, as well as the HL1 LED, can be removed without compromising the operation of the circuit.

The signals from the outputs of the DA3...DA5 switches can be fed without electrical mixing on the R35 potentiometer directly to the inputs of individual low-power ultrasonic frequencies with narrow-band miniature sound emitters. Mixing of signals in this case will be carried out acoustically.

This unit can also be used in multi-channel dynamic color setups. In this case, the device circuit can be significantly simplified by turning on instead of the HL2 ... HL13 LEDs (or in series with them) the LEDs of the optocouplers connected to the thyristor or triac control circuit.

The device consumes 60 mA at a supply voltage of 15 V and one glowing LED; at 12V - 50 mA, at 9V - 35 mA. In the latter case, the frequency/voltage conversion characteristic changes markedly.

Literature

1. Shustov M.A. The use of polycomparator microcircuits in radio communication technology. - Radio amateur, 1997, N6, S.13-15.

Author: M. Shustov, Tomsk; Publication: N. Bolshakov, rf.atnn.ru

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