In this article explains how to make Subwoofer Amplifier with simple steps by using a circuit diagram, this subwoofer amplifier circuit is very simple and it consists of power supply and audio amplifier parts. The simple schematic diagram of the two-channel amplifier to be driven from two inputs left and right channels facilitate a hassle-free bridge mono mode operation. This subwoofer amplifier circuit consists of a TL072 low-noise JFET dual operational amplifier (IC1) and two LM1875 (IC2 and IC3) power amplifiers.
LM1875 Power Amplifier Circuit Diagram
Subwoofer amplifier Circuit operation:
- In stereo mode, each half of the TL072 operates as a non-inverting input amplifier, with a gain of about 2.8 times as determined by feedback resistors R5 and R6.
- In front of each input amplifier, there is a low-pass filter for RF suppression (R1/C1 and R15/C12), followed by the volume controls VR1 and VR2 and blocking capacitors C2 and C13.
- Switch S1 is used to select bridge mono mode operation. When it is switched to mono position ‘M‘, the non-inverting input of IC1(B) is connected to the ground, making the left input of the brick ineffective.
- At the inverting terminal of IC1(B), the cold end of the resistor R13 is disconnected from the ground and connected to R7.
- It is now converted into a unity gain inverting stage and the output of IC1(A) is connected to IC1(B) through R7.
- This converts the front end to produce dual-phase drive signals from the right channel input.
- In stereo mode, each of the amplifier stages drives the right and the left speaker connected across pin 4 of IC2 and IC3, respectively.
- Each input stage drives one of the LM1875 power stages (IC2 and IC3) with traditional circuitry. Coupling capacitors C7 and C14 provide DC blocking, with the power stage voltage gains set to around 18 by feedback networks R9/R10 and R20/R21.
- Output stages operate from DC rails of ±21V, which are provided from the power supply, using 21V-0-21V, 2A center-tapped transformer.
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