Active bass speaker circuit, power amplifier circuit

Circuit introduction

The speaker signal is input from the two lotus sockets of RCA1 and RCA2. After the L_R channel audio signal is input, it is isolated by R1 and R2 resistors, and then mixed and divided by R3-R4, and then the signal enters the IC1 operational amplifier circuit. The Ic1b operational amplifier unit in IC1 operational amplifier, together with peripheral components such as R4~R6, w1~w1', c2~c3, form an RC second-order low-pass frequency-selective active filter circuit. This circuit has a 12dB attenuation slope characteristic per octave, and can achieve the best sound synergy and balance with the main speakers by adjusting the w1 (w1') coaxial double potentiometer and controlling the circuit's low-frequency frequency selection frequency. . When adjusting w1 (w1'), according to the circuit component parameters. The frequency selection frequency can probably be in the range of 150Hz ~ 1kHz.

After IC1b circuit. It consists of R6~R8, C6 and IC1a op amp unit. Form a buffer amplifier circuit. A low-frequency signal that is boosted after amplification. Then from IC1a⑦ pin. Output to the w2 potentiometer; W2 can complete the volume control operation of the speaker.

The audio signal on the volume potentiometer W2 is sent to the final power amplifier circuit. Its circuit consists of two "LM1875 model IC power amplifier integrated circuits (the two power amplifier blocks IC2 ~ Ic3 form a bridge output BTL power amplifier circuit with larger output power). The circuit has low distortion, high common mode rejection ratio, stable performance, It has the characteristics of high power utilization. Moreover, the LMl875 power amplifier IC circuit has a mellow tone and has the flavor of a tube amplifier! In order to give full play to the tone performance of the LMl875, the feedback link is eliminated. capacitance to make the circuit "DC"; thereby further broadening the audio bandwidth), but there is no mid-point operating potential deviation. , overload self-protection function), during actual production, the speaker manufacturer also installed a 230mm×115mmx2mm large-area aluminum radiator on IC2~Ic3, which can further ensure the working safety of IC2~Ic3.

The power supply of the final power amplifier is powered by the "±DC25V" voltage obtained from the double "AC20V" voltage on the secondary side of the transformer, rectified and filtered by D1~D4, C23, and C24. The power supply of the front-stage IC1 (a~b) circuit is "±DC25V" power supply. Through R25→c21→D5, R26→C22→D6 circuit voltage stabilization, a set of "±DC12V" voltage is obtained to provide power supply operation.