AVK200 home theater amplifier and maintenance 05

(5) Tone, equal loudness, CD pass-through control circuit
    The tone control of this machine adopts RC attenuation circuit. The operator feels more intuitive and there will be no jump phenomenon.
    The equal loudness circuit is connected to the master volume controller part. When the total volume potentiometer is set to the volume position below 1/3,
the high and low frequency (resonance points are 10kHz and 100Hz) components in the left and right channel signals can be improved by more than 3dB. The on and off of the equal loudness circuit
is controlled by a direct key switch.
    The purpose of setting up the CD pass-through function is to facilitate users to use the machine as a power amplifier when decoding and other functions are not needed,
thereby reducing distortion and facilitating music appreciation. The principle of the CD pass-through function of this machine is: 1N2 sends an instruction
to 2N7. The high level output by 2N7 turns on 2V4, the normally closed contact of silver-plated contact relay 2K1 is disconnected, and the normally open contact is closed.
The signal input from the CD/I-D interface bypasses the decoding and tone circuits and directly enters the balance control to the total volume. At this time, other interface
inputs are invalid, and the center and surround channels are turned off.