Vermes
Advanced Member level 4
It is a car subwoofer amplifier 70W with an active low-pass filter with adjustable cut-off frequency of about 20-200Hz. The amplifier is based on an integrated circuit TDA1562(Q) with charge pump, powered by 14,4V car installation. The whole is placed on a PCB with dimensions of 8,5cm x 5,5cm. Advantages of the device: low cost of implementation, simple design, pretty good performance.
TDA1562Q is cheap and simple. It contains a charge pump, which increases the voltage of the amplifier. Capacitors of minimum 4700uF should be attached to the feet of charge pump. The system is not suitable for use with low frequencies due to the type of voltage converter. The capacity should be raised to 10000uF...20000uF (or more) when you want the capacitor to work better at low frequencies. In this case, 6 capacitors 4700uF/16V were used. Capacitors 16V are fully sufficient. With less power, the amplifier works in class AB with power up to 20W, then automatically starts the charge pump and works in class H, offering up to 70W with 14,4V power supply, what is exactly as much as a car installation gives. The structure also provided a number of current, thermal and anti short-circuit protections, overload detection, measurement of distortions or overload. The system also has a diagnostic and status output. A LED, that would light if the system detects any irregularities (too high temperature, distortion etc.), should be added to the diagnostic output. The system also switches itself to class AB, when it overheats or is charged with too much shock.
Low-pass filter is a double-row filter (12db/oct) with adjustable conquest and adjustable upper limit frequency from about 20Hz to 200Hz. That allows thoroughly testing and selecting the frequency of subwoofer operation. Originally, this regulation was to 100Hz, the change of double potentiometer 2x10K to 2x20K increased this range (in the diagram there is 2x10K). The filter is powered by a single voltage directly from the car installation, there are capacitors 1uF before and after the filter. They provide suitable constant component in the signal. Artificial mass is provided by two resistors 1K. Voltage is filtered by a large capacitor 4700uF/16V and a less one 100nF, which damps the noise at higher frequencies. In addition, the power supply from the point BAT is routed through the fuse 10A. At currents which are provided by the accumulator, there could be a fire of the installation, so the fuse should always be of the appropriate value. Rectifying diode protects the whole against reverse connecting the power supply, it should be stronger than the applied fuse – on the diagram it is 1N4004, but it should be high power (e.g., from the ATX power supply), preferably from the bottom of the plate. Circuit of the amplifier charges up to 8A current, so the connection cable should be at least 2,5mm^2. The mass can be taken from any point, such as structural element of the trunk. Amplifier's system requires cooling. For this purpose a small heat sink should be tightened to it. The amplifier is automatically switched on along with the player, so the MODE input is used. The input is connected to control output of the player. So when the radio is turned off, also the amplifier is off. On the plate, there are pin connectors to connect the signal, on the left SUB and IN. SUB input is through the filter, IN reaches directly to the amplifier. The second four-pin connector is to connect the control diode (pin 2 (the diode) and pin 4 (+power)), and to connect the signal from the radio activating the amplifier (pin 1 (the mass) and pin 3 (signal +12V from the radio).
Prototype plate in the picture differs from the plate in the device. In the place of capacitors, 2x100nF (in case of 200nF) and 180nF+220nF or 4x100nF (in case of 400nF) should be soldered. Potentiometers to adjust the amplify and cut-off are located on the side of the plate, so that they can be immediately brought outside. All the capacitors 4700uF should be up to 16mm diameter. Two connections by wires should be performed on the plate. First one from the power source to TDA1562 system with wire as thick as possible. The second one to the low-pass filter of any diameter. Current paths are quite wide and it is no need to thicker them. Amplifier circuit pads are small, the holes should be drilled with 0,8mm drill.
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Link to original thread (attachment) – Samochodowy wzmacniacz subwoofera 70W
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