Before you think about this, please ensure you properly connected the power supply. The wire which is connecting to the top heat fuse of the transformer and going down to transformator core has the biggest capacitance, so here you should connect null, while the other wire should be the 230V phase.

This is fine for 50Hz, but frequencies generated by switching power supply are bypassing easily. The below opinions are to improve this area.

I had some leftover EMI/RFI filter from an old ~200W computer power supply, I decided to give a chance as the filters designed for audio applications are identical. Below you can find the schematic of such filter, but note: You will need functioning “Protection Earth” (PE), so I replaced the power cord. The amp luckily is prepared for such cable, so next to the main switch there is an easy connection with a screw lock. Note: This increases the safety of the product. Is a huge risk not having PE connected.

But note: The filter reduces noise on the AC line on the cost of the PE. While connecting PE to house may lead in noise… So not an easy task to decide between safety and best sound.

My recomendation from sound perspective is to not use PE and be very careful

and

to plug out all switching power supplies in the houshold. If you can’t do these only then recommend you to build this modification.

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