The 20-W + 20-W stereo amp consists of two complete, separate 20-W RMS bridge-type amplifiers. The input signal source is brought into the amplifier through the voltage divider network, which is made up of Rl, R2, and PI. Resistor Rl provides a load impedance between the signal source and ground. Resistor R2 couples that signal to potentiometer PI.The signal is coupled by capacitor CI to the noninverting (+) input (pin 1) of internal amplifier (A) of IC1, where the signal is greatly amplified. Capacitor C2 couples the (+) input of the other (B) internal amplifier of IC1 to ground. That causes the input signal, which is referenced to ground, to be coupled to both amplifiers because both the inputs and outputs of IC1 (A) and IC1 (B) are connected in a bridge configuration. Notice that the output of IC1 (A) from pin 10 is connected to one side of the speaker and the output of IC1 (B) from pin 8 is connected to the other side of the speaker.That is why the speakers used cannot have one side connected to ground. Resistors R6 and R7 set the gain of the amplifier. Resistors R9 and R10 and capacitors C9 and C10 provide frequency stability and prevent oscillation. Capacitors C6 and C7 provide bootstrapping, which prevents distortion at low frequencies. LED LI lights up by way of a series resistor connected from the anode to +12 Vdc when power is applied.Power for both IC1 and IC2 is brought in through D1 (to protect amplifiers from reverse polarity). Capacitor Cll provides additional power supply line filtering. This booster is capable of producing 20 W RMS output out of each channel.
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