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LM1875 based BTL application experiments and current-feedback design circuit

DC of the current negative feedback circuit applications OCL

LM1875 based BTL application experiments and current-feedback design circuit 1

Click "Newsletter" in 2001 27 "LNl875 amplifier made to understand" the ridge of the circuit (Figure 1) The experimental results were indeed as stated in the text, and instead of a dc current feedback, the frequency response widening, bass intensity increased significantly increase the frequency resolving power, midrange texture enhanced sound quality improved a lot compared with the standard circuit, so long to listen into the tire, using this amplifier with the new Pure Class A power amplifier 6800 compared Dirk Love, pushing Swans Swan M1.2 Speaker, 15 square meters room, about the output of about 10W, very close to the new Texas sound machine, sound, air force, resolving power comparable with them. LMl875 treble delicate point, the thickness of the new strong vocals Dirk 6800 - point difference between the two small, unexpected.
But LMl875 DC current negative feedback circuit of the shortage also makes people feel something missing: the power is too small, the static could be heard when the exchange of sound, measured LMl875 static output to more than a few mV of the voltage.
LMl875 DC BTL design of current negative feedback

LM1875 based BTL application experiments and current-feedback design circuit 2

BTL DC current negative feedback circuit of Figure 2, the abolition of the standard BTL circuit C12, C22, DC of the circuit; resistors R16 and R26 is the sampling resistor, current feedback signal via R15, R16, R25, R26 respectively to the amplifier A1, the inverting input of A2, R13, R14, R15, R16 determine the resistance of the amplifier gain size.
  Circuit in Figure 2, in any case off power and input signal, the output has not DC output, and there is no static output noise, speakers, only a slight boot "A pair of" sound, no noise, turned off the speakers can be heard. The experiment shows that such input circuit is very stable, even in large volume or static open input terminals will unplug and then plug the circuit will not self-excited. Capacitor C11 a great impact on the sound quality, remove the capacitor, the eyes immediately light up, alt become clear detail, bass flexibility and strength. BTL DC current negative feedback circuit of the DC inherited OCL current negative feedback circuit of the advantages of quality, further reduce distortion, the output power increased to 3 times the original, up to 60 watts or more, to overcome the switch has an impact speaker acoustic and static hum when the shortcomings of the circuit is the LM1875 ideal for optimization.