Lm1875 application experiment and current feedback btl circuit design circuit diagram

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After the circuit is DCized and changed to current feedback, the frequency response is widened, the bass power is obviously enhanced, the high-frequency resolution is increased, the mid-range texture is enhanced, and the sound quality is much improved compared with the standard circuit, so that it can be used for a long time, using this amplifier and Xindak. 6800 pure class A power amplifier contrast audition, push Huiwei swan m1.2 speaker, 15 square meters room, about 10w output, the sound is very close to the new Dirk machine, sound power, resolution is comparable. Lml875 high-pitched and delicate, Xindeke 6800 voice thickness is strong - point, the difference between the two is small, unexpected.

However, the lack of lml875 DC current negative feedback circuit also makes people feel that if it is lost: the power is too small, there is audible hum sound when static, when the measured lml875 static output has a few to ten mv voltage.

DC current negative feedback btl circuit shown in Figure 2, cancel the standard btl circuit c12, c22, make the circuit DC; resistor r16 and r26 is the sampling resistor, the current feedback signal through r15, r16, r25, r26 into the amplifier a1 The inverting input of a2, the resistance of r13, r14, r15, r16 determines the magnitude of the amplifier gain.

Using the circuit experiment of Figure 2, no matter how the power and input signals are turned on and off, there is no DC output at the output end, and there is no static output noise. There is only a slight “beep” sound in the speaker when the power is turned on, and there is no noise in the speaker when the power is turned off. It can be seen from experiments that the input circuit works very stably. Even if the input terminal is unplugged and plugged in when the volume is turned on or static, the circuit will not be self-excited. Capacitor c11 has a great influence on the sound quality. After removing this capacitor, the front is bright, the middle and high notes become clear and delicate, and the bass is flexible and strong. The DC current negative feedback btl circuit inherits the advantages of the direct current negative feedback ocl circuit sound quality, the distortion is further reduced, the output power is increased to 3 times, reaching 60 watts or more, overcoming the impact of the switch speaker. The shortcoming of humming sound in both sound and static is the ideal optimization circuit for lm1875.