High fidelity BTL amplifier circuit

High-fidelity BTL amplifier Here we introduce a BTL power amplifier circuit that does not require debugging, has high fidelity and is low-cost. You can choose the final power amplifier integrated circuit according to your own situation. Due to its strong versatility, it brings great benefits to audio enthusiasts. Great convenience. Working Principle  　　The working principle of the device circuit is shown in Figure 1. Only the circuit diagram of one channel is given here, the other channel is exactly the same. The audio signal is input from the A terminal of the circuit and is amplified by the operational amplifier IC1 (the amplification factor is determined by R1 and R2). One channel is inverted and amplified by IC2, with a gain of 1; the other channel is inverted and amplified twice by IC3 and IC4. , the gain is still 1. The essence is that IC3 and IC4 together form a positive-phase amplifier with a gain of 1, so what is obtained at the B terminal of IC2 and the C terminal of IC4 are two audio signals that are equal but opposite in phase. These two mutually inverted audio signals are added to the ① and ⑤ pins of the dual audio power amplifier integrated circuit IC5 (TDA2009) through R9, C5, R10, and C6 respectively. These two input terminals are non-inverting input and inverting input. terminal, so after power amplification is performed inside IC5, it is output from the ⑩ pin and ⑧ pin of IC5 respectively to drive the speaker BL. The component selection and debugging component list is shown in the table below. No. Name Model Quantity No. Name Model Quantity R1 Resistor 1K 1 C11 Electrolytic capacitor 47u 1 R2, 20, 21 Resistor 10K 3 C12, 13 Polyester capacitor 0.1u 2 R3, R9, R12 Resistor 220K 3 C14 Electrolytic capacitor 10u 1 R4-R7, 10, 11, 13, 16 resistor 20K 8 C15 ceramic capacitor 0.01u 1 R8, 14, 15 resistor 100Ω 3 C16 electrolytic capacitor 100u 1 R17, 18 resistor 10Ω 2 DW Zener diode 20V 1 R19 resistor 2.7K 1 VT transistor 2N5551 1 C1, 3, 4, 5, 6 electrolytic capacitor 1u 5 IC1 quad operational amplifier IC TL084 1 C2 electrolytic capacitor 4.7u 1 IC2 two-channel power amplifier IC TDA2009 1 C7, 8 ceramic capacitor 1000P 2 BL speaker 4-8Ω 1 C9, 10 electrolytic capacitor 220u 2 IC1-IC4 can use a four-op amplifier integrated circuit TL084. The differential amplifier has wide frequency response, low noise, and high transient indicators. In addition to using TDA2009, the power integrated amplifier can also use other similar integrated circuits without special requirements. All resistors used are low-noise, precision metal film resistors. The purpose is to reduce the noise of the pre-stage. At the same time, the signal amplitudes at points B and C should be equal. The coupling capacitors used in the pre-stage should also be precision tantalum capacitors. . The power of the transistor VT should depend on the current required by the circuit, and there should be sufficient capacity reserve in order to obtain good transient characteristics and sufficient dynamic range. Due to the versatility of this circuit design, any OTL or OCL output dual-power amplifier integrated circuit can be connected to the B and C ends of the differential amplifier to form a BTL amplifier. If readers are interested, they can also insert an RC attenuation tone control circuit, which will give better results.