Power supply protection circuit against main supply ?

[Speedskater]

Some incandescent bulbs produce an arc when they fail, often blowing a fuse. This sudden surge in current, followed by a sudden drop, will maximise any back emf from the inductance of your mains wiring. My guess is that inductance can be increased by the habit of some electricians (in the past?) to use individual wires in conduit rather than a multi-core cable (e.g. twin and earth). Curiously, this form of wiring was/is regarded as 'more professional' than multi-core. Now if they twisted the wires together this would reduce inductance but they never do this because it makes it much harder to pull a wire through the conduit.

Most older US homes (pre 1950) were wired with widely spaced wires. Known as "Knob & Tube" wiring, the conductors were spaced from 6 to 12 inches apart (150mm to 300mm). These homes don't seem to suffer from high inductance problems.

 

[guitar89]

well, The reason I wanted to DIY is that it cost much for me.
Not because it is expensive, but it is design for higher ampere (like 15A or 30A), this increase the cost. while mine is only about 2-3A.
Another reason is that I need to bring here&there with a power cord. It is a hassle to do that. I wish for something inbuilt within amplifier, or a small one.(very portable type)

 

[FRANK BRAUN]

put a varistor (MOV) across the trafo windings, then put a fuse on one of the mains supply line to your project before the MOV and trafo. better yet put earth grounding to your projects' chassis vs thunderstorms.