sound exciter

The actual circuit of the exciter is shown in Figure 1-126. The audio signal is input to the inverting buffer iqA via cr and RI, and its
pin 7 output signal is divided into two channels. One channel is directly input to the synthetic output stage composed of iqD. The other input is a voltage-controlled variable high-pass filter
composed of iqB and IC3A and IC3B through R7 . Its turning frequency is determined by Rl5, Rzs, q, cll and Ic internal voltage-controlled variable transconductance components, and is passed through the potentiometer The adjustment of RPi causes the corner frequency to change between 2 and 8kHz, and the signal below the corner frequency is attenuated by 12dB octave. Adjusting RPZA can change the amount of negative feedback from the bandpass output of IC3A9 pin to the inverting input terminal of IClB9 pin, thereby changing the Q value of the filter, because Q=(氰‰+Rg)/ R ll, the adjustment range of the port value is l- 0~1,50IC3 is a dual operational transconductance amplifier, model 13600. The internal principle is shown in Figure 1-127(a). R27 and R4l are 13600 internal emitter output load resistors, so they must be connected to the negative power supply. At the same time, the output terminals of pins 9 and 8 of IC3 are kept at zero potential to the ground. Pin ICIB8 is the output end of the voltage-controlled state variable high-pass filter .