January 12, 2015

DIY LM1875 Gainclone Amplifier (Part 3) The Power Supply Section

Continue from the previous post, which I prepare for the amplifier casing taken from my old project, then the next step is assembly all amplifier components inside the casing. This is because I am not using any PCB at all. Connection between components will be point-to-point connection. I will start from the power supply section first.


The toroidal transformer that I mentioned before is the dual rail secondary output. This is means the output is 2 pair of voltage. When I am using diode bridge rectifier for each output, then I can have more linear DC power supply.
 

Then I am joining primary transformer to the AC socket terminals. In this stages, the power supply section ready to test for the DC output after the rectifier.


After all connection are done properly, I put Nichicon Muse capacitor for each DC output from the rectifier. They are directly solder to the rectifier pin.


In this build, I will experimenting that the ground loop circuit at the AC ground terminal to the casing ground for better safety reason. The circuit consist only using 2 diodes in each polarity reversed, one 15 ohm/ 5watt resistor and 100 nF 400 volt capacitor, all tied in parallel.





The last step is put the L shape aluminum that can be use for the heat sink the rectifier bridges. The main purpose for this aluminum is to avoid the electrical noise from the transformer to the amplifier circuit next to it. This is technically finished for the power supply section.







I add another work in this amplifier. I connect the speaker cable to the speaker connector switch since I have more room for doing it now. As I explain on the part 1, the purpose of this switch is manually connect between amplifier to speakers to prevent pop noise during turning ON or OFF. All of the LM1875 Gainclone amplifier will suffer from this noise issue.


The switch connection will be looking like this.


I preparing for the amplifier section by put another L-shape aluminum heat sink.


This heat sink is for the LM1875 amplifier.


I put the LM1875 on it and put the washer and isolator between them to avoid short circuit.



The part 4 can be find here

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