The Principle and Design of High-Fidelity BTL Amplifier

The Principle and Design of High-Fidelity BTL Amplifier

　This article introduces a BTL power amplifier circuit that does not require debugging, has high fidelity, and is low in cost. You can also select the final power amplifier integrated circuit according to your own situation. Due to its strong versatility, it brings great convenience to audio enthusiasts.
　　Working principle     High-fidelity BTL amplifier (TDA2009)
. Only the circuit diagram of one channel is given here, and the other channel is exactly the same. The audio signal is input from the A end of the circuit, amplified by the operational amplifier IC1 (the amplification factor is determined by R1 and R2), one way is inverted amplified by IC2, and its gain is 1; the other way is inverted amplified twice by IC3 and IC4, and the gain is still 1. In essence, IC3 and IC4 together constitute a positive amplifier with a gain of 1, so two equal and opposite phase audio signals are obtained at the B end of IC2 and the C end of IC4. The 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 and R10, C6 respectively. These two input terminals are the same-phase input and the reverse-phase input terminals. Therefore, after the power is amplified inside IC5, they are output from the ⑩ and ⑧ pins of IC5 respectively to drive the speaker BL.
　　Component selection and debugging
　　The component list is shown in the table below.
　　The working principle of the device circuit is shown in Figure 1

　　IC1-IC4 can use a four-op-amp integrated circuit TL084. The differential amplifier has a wide frequency response, low noise, and high transient index. In addition to TDA2009, other similar integrated circuits can also be used for the power integrated amplifier 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 pre-stage coupling capacitors used should also use precision tantalum capacitors. The power of the transistor VT should be determined by the current required by the circuit, and there should be enough capacity reserves to obtain good transient characteristics and sufficient dynamic range.
　　Due to the versatility of this circuit design, any dual-power amplifier integrated circuit with OTL or OCL output can be connected to the B and C ends of the differential amplifier to form a BTL amplifier. If the reader is interested, you can also insert an RC attenuation tone control circuit, which will achieve better results.