40W power amplifier composed of LM3875

LM3875 is a monolithic integrated power amplifier circuit launched by National Semiconductor. In the frequency range of 20№ to 20kHz
, when the load is 80, it can continuously output an average power of more than 40W, with a total harmonic distortion of only
0.05%. The overvoltage, undervoltage, overload, short circuit and high temperature protection functions of the circuit are the same as those of other LM series power amplifier circuits
. It has excellent performance, simple peripheral circuit, easy and reliable use.
    Figure 2-56 shows the application circuit of LM3875. This circuit uses LM833 as a preamplifier to form a complete
40W power amplifier circuit. Although the preamplifier LM833 is not as well-known as the NE5532 , its performance indicators
are comparable to the NE5532 and has been adopted by many audio manufacturers. The performance comparison of the two integrated blocks is shown in Table 2-13. It has excellent performance in vocals and
violin strings. The performance is round and delicate, which is better than that of NE5532 , indicating that its transient distortion index is quite good. The gain of this circuit
for the LM833 is not high, only more than 4 times. It amplifies the 200mV input signal to nearly lv, and can drive
the LM3875 to full power. If the gain of the pre-stage is too high, the amplified signal will inevitably cause the input signal of the power amplifier stage to be overloaded,
resulting in transient distortion. Leaving most of the gain to the power amplifier LM 3875 can prevent clipping distortion at the input end when the signal is large
.