I finally attempted to re-cap a 1980s stereo receiver with modern capacitors, but the left channel now has a faint hum that wasn't there before.

I learned that just matching the microfarad and voltage ratings isn't always enough, so has anyone else dealt with a new hum after a recap and figured out the specific cause?

3 comments

3 Comments

rosew372mo ago

Ugh, did you maybe knock a ground wire loose while you were working in there? I tried to fix a busted lamp once and somehow made it buzz like a hornet's nest, so I feel your pain. Honestly, I've read that using caps with the wrong ESR, that's Equivalent Series Resistance, can cause noise issues in old audio gear. Maybe check if any of your solder joints look cold or cracked, that's a classic hum culprit too.

wesleypatel1mo ago

Yeah cold solder joints are a killer on vintage gear. I've had to reflow half a board before just to kill a hum. And yeah ESR matters way more than people think with these old circuits.

campbell.logan2mo ago

Had the same exact problem with an old Sansui last year. Traced it back to a single new capacitor I'd put in the power supply section for the left channel. Swapped it out for a low ESR type, like a Panasonic FC, and the hum just vanished. Sometimes the old circuits are really picky about that stuff. Also double checked my ground connections on that side, one was a bit iffy.