Introduction to Audio Amplifier Circuit Designed by LM307 and μA741

Probe domestic high frequency needle JKT-50L high frequency needle with 3 probes

As shown in the figure, a simple audio amplifier circuit. An audio amplifier composed of an integrated operational amplifier is stable in operation and easy to add negative feedback, so it is easy to obtain equalization characteristics. In addition, crosstalk is small between channels, and it is easy to mix and match multiple channels. The circuit shown in Figure (a) uses dual power supplies (Vs = ±15V). The static resistance of the in-phase and inverting input terminals to ground is basically balanced. The input signal Vi is fed into the non-inverting input of the LM307N by a 0.1μF coupling capacitor. Feet 3). For the signal source, its input resistance is about 1MΩ, so its equivalent load is very light. The circuit has a voltage amplification factor of about 101 times and has good dynamic characteristics. The circuit shown in Figure (b) is powered by a single power supply. This type of power supply is desirable because there is no DC level problem with the signal in the AC amplifier. In this circuit, the audio signal K is fed through the coupling capacitor C and the resistor R1, and the inverting input of the μA741C (pin 2). It can be seen from the figure that the circuit introduces 100% negative feedback to the DC component (c is relatively open to the DC component), so there is no amplification effect on the offset voltage. The voltage amplification factor of this circuit is: Av = -R2 / R1 = -1000 (ie 60dB). However, it should be emphasized that R1, R2 and capacitor C have low frequency attenuation and phase shifting. When the signal frequency is low, the capacity of capacitor C can be appropriately increased.