I am building an amp for 6th order subs which is based on two transformers which have around 25 VAC, and I am trying to rectify them for 2 subwoofer module filter boards (12-32vdc) and for two TDA7498. Each pair has its own transformer.

I tried my luck first with one eBay board based on some LM voltage regulator but the TO220 literally exploded despite the fact that it was rated to 25 VAC. I figured it could be the current was too large. So I brought bigger rectifier boards based on xl4016 which should accommodate up to 25 VAC @ 6 amps. I have used these with 2.1 tpa3116 and various Transformers around 25v and they have been working flawlessly.

I still have one module which works in my system well. I ordered 3 new . I used first one set that on open voltage of the transformer to 24 vdc so I don't fry my amp and module and then I connected it (actually turned off connected and turned on). What follows was basically very wild release of fumes from one cap on the board. I was prepared for such situation so I didn't inhale anything(after my unlucky experience with cadmium oxide in thermorelay from eBay).

I measured before failure 34 VDC output as if output pot failed and send through only rectified voltage from bridge. Why did capacitor exploded on this module and not on the other module? I put textile tape to prevent short-circuit because boards are attached to metal. Could over-voltage of AC (extra 1.5-2Volts)caused the faiure? is that a significant problem tuning the pot to lower voltage then input ac voltage? If input is AC25v and I set it on the pot to 24vdc do I cause somewhere excessive heat? Thank you

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  • \$\begingroup\$ Board on the left old one works, board on the right the blue cap blew right after taking the picture. \$\endgroup\$ Jul 11 '20 at 22:41
  • \$\begingroup\$ Welcome. I parsed your wall of text into paragraphs, as much as they are of different context. In the future please write in paragraphs based on transitions in content or context. \$\endgroup\$
    – user105652
    Jul 12 '20 at 2:25

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