Tried recapping an old stereo amp from 1982 and made it sound worse somehow

Honestly I swapped out all the electrolytic caps on a Pioneer SA-7500 last weekend expecting a nice clean sound upgrade but instead got this weird hum that wasn't there before. Has anyone else run into new caps causing noise issues or did I just grab a bad batch from the supply shop?

3 comments

3 Comments

jade31mo agoMost Upvoted

88s pioneer gear is usually pretty forgiving but that 50/60hz hum you are describing sounds like a grounding issue. Did you check the new caps polarity twice? I made that mistake once on a marantz and it hummed like a angry bee until I flipped the two that were backwards.

harper_murphy1mo ago

Oh man, that exact thing happened to me on a Sansui 771 last year! I was so sure I had the caps lined up right but nope, two were reversed and it sounded like a buzzing transformer until I swapped them. Grounding issues are tricky like that, especially when you're swapping parts one at a time and not thinking straight.

susan_ward19d ago

Your grounding guess makes a lot of sense. When you swap out the old caps, sometimes the solder joints end up bridging to a ground trace that was fine before, especially on those Pioneer boards where everything is packed tight. I also learned the hard way that new caps can have a slightly different diameter on the leads, and if they don't seat fully flush against the board, the vibration from the transformer can cause that hum to pop up. Might be worth reflowing all your ground connections and making sure none of the new caps are physically touching the chassis or a heat sink.