A Class D Bass Amplifier

1. The crossover inductor of the speaker weighs kilograms, has high cost and large distributed parameters, which will affect the improvement of sound quality.
2. The dynamic range of the power amplifier is limited, and the high-power low frequency affects the reproduction of the treble. Especially for Class A power amplifiers, the treble becomes smaller and hoarse.
3. The power amplifier generates serious heat and requires a large heat sink, which increases costs and power consumption.

Based on the above considerations, in order to give full play to the high sound quality of the existing Class A amplifier and enjoy the shocking bass effect at the same time, the author designed this Class D bass amplifier. We know that the efficiency of Class D amplifiers is very high, and the lower the frequency, the smaller the distortion. The human ear is not sensitive to low frequencies, so Class D is used. The peak power of this amplifier can reach 350W, and it is almost unnecessary to use a radiator. The original bookshelf speakers plus a passive subwoofer can form a complete sound system.

The principle is shown in the figure. The sound signal is introduced from P1 and P2, and after buffer isolation and active high-pass filtering, it is connected to the original power amplifier system through P3 and P4. Because there is a buffer stage, the left and right channels have a high degree of separation. Since the frequency components below 150Hz are filtered out, the burden of the original system is effectively reduced, ensuring that the entire system has a large dynamic range. The signal after high-pass filtering enters the comparator U2A after adjusting the volume through R11. U2B and U1 form a sawtooth wave generator with a frequency of about 100kHz. U2A compares the signal with the sawtooth wave to obtain a PWM wave, which drives the subsequent stage to work in the switching state, effectively reducing the power consumption of the subsequent stage. Q1 and Q2 are driving tubes, and high-frequency pairs with a current greater than 20A can be used. The author uses IRF150 (40A, N channel) and IRF9150 (40A, P channel). C11 is a protective electrolytic to protect the speaker from being damaged by DC. The larger the capacity, the better.

L1, L2, C1, C2 are filter components. To prevent the influence of 50Hz AC, the larger the better. The withstand voltage of the capacitor should be greater than 100V. There is no filter network at the output end, because the subwoofer speaker has high impedance to the 100kHz switch component, and it cannot be heard even if it is released, so it is omitted. The main thing to note is that the digital part (U2, U1, and the rear stage push tube) must be effectively isolated from the filter part, especially the U5 part, which must be grounded over a large area. It is best to use a separate power supply and wrap it with copper foil. All circuit wiring should be reasonable, the wiring should be as short as possible, it is best to ground at one point, and the high current part should be tinned on the copper foil. The chassis is best to use metal and grounded, and it can also form an active subwoofer with the subwoofer. Q1 and Q2 can be slightly cooled. The entire circuit can work without debugging, I believe you will not be disappointed.