How to use switching power supply replacement amplifier transformer
An amplifier toroidal transformer burned due to overheating, has been unable to see the nominal voltage, and no wiring diagram, can only be based on observation to determine the parameters. The transformer secondary a total of six output lines, three of which are connected to the amplifier board, rectified to provide positive and negative voltage for the amplifier circuit. Observe the amplifier board has two 10000μF/50V electrolytic capacitors as a filter. Estimated supply voltage will not be higher than 40 V. The other three wires to the front panel, one of which is connected to the display filament terminal for the filament power supply (estimated voltage of 6 V or so), the other line by the half-wave rectifier and 100 μF / 35 V electrolytic capacitor filtering for the display and the electronic switching circuits power supply (estimated voltage of +30 V or so. This is not the same as the common -30 V or so. This is different from the common -30V power supply), the rest of the line for the public ground. I chose the "Huazhou brand audio dedicated 150W switching power supply board" for replacement. The main output voltage of the power supply can be adjusted from ± 22V to ± 32V, there is a 8-12V secondary voltage backup. Replacement, first of all, remove the original transformer, the switching power supply on the main voltage output and the power supply of the amplifier board connected to the corresponding end. Then from the main voltage output of the switching power supply to connect a lead to the panel display and electronic switching circuit power supply. Finally, the secondary voltage output from the switching power supply by a 5V regulator block 7805 regulated to the display filament power supply (see attached figure). Because of the original panel with the pre-circuit connected to the ground line, it can not be connected to the ground.
Connected to the ground line, it can not be connected to ground. To prevent self-excitation.
After the wires are connected, before switching on the switching power supply board on the voltage adjustment potentiometer rotated to the middle position.
To prevent excessive voltage damage to the amplifier circuit. Then switch on. Observe the main power output voltage is ± 25V. At the same time, I heard the sound of the relay on the amplifier board. Then look at the front of the display has been lit, measured the display filament power supply is stable 5V. Although slightly lower than the rated value of 6V.
But the screen brightness is OK. Press the micro switch on the panel, the electronic switching circuit can be switched normally.
Connected to the speaker, inserted into the signal source test machine. Speaker comes out in a beautiful song. The end of a song, the static noise in the speaker is very small, feel better than ordinary transformer power supply. Try to gradually open the amplifier volume. When the volume is opened to 60%, it feels that the song is a little hairy. It is estimated that the output voltage of the power supply is too low, the voltage will be adjusted to ± 32V test, hairy phenomenon disappeared, bass thick. Treble clear. Turn off the machine after two hours of continuous trial at high volume, touch the power board on the power tube heat sink is only slightly hot, proving that the power supply is working stably. Finally, the power supply board properly fixed in the original toroidal transformer, replacement work is over.
