I need help with a very strange problem: A friend's stereo system ran for about 8 years without any problems. The wiring is behind a permanently installed sideboard and has never been moved even 1 mm in that period. Suddenly and without any apparent cause, a loud, nasty humming sound is coming from the speakers. It sounds like the typical hum of a ground loop, but overlaid with a "hard component". The hum is also there when the volume on the preamp is turned down to zero.
Okay, I'm happy to help ... I have torn apart all the wiring and put it back together, taking great care that the signal cables and the mains cables do not overlap anywhere. The mains cables are all in the same multiple socket. The tuner is connected to the house aerial with a sheath current filter. In short, all the usual measures to avoid ground loops and interference have been taken.
Now it comes: Everything works wonderfully - dead silence. I increase the volume and the music plays pure and clear - hurray! Increase the volume further and BRRRRRRRRMMMMMM - it hums as before. Turned the volume back down to zero, the loud hum persists unchanged. I will spare you a description of what I tried and come to the moment when I gave up:
If I disconnect any speaker plug from one of the two stereo power amplifiers (the whole thing is two-way active with active crossover) the hum disappears on all channels. When I put the speaker plug back in, the hum is back and only disappears when one of the power amplifiers is switched off. Swapping the power amplifiers (left to right and vice versa) makes no difference.
WHAT THE F**K IS THAT?
Thank you for your attention ... 😳
Okay, I'm happy to help ... I have torn apart all the wiring and put it back together, taking great care that the signal cables and the mains cables do not overlap anywhere. The mains cables are all in the same multiple socket. The tuner is connected to the house aerial with a sheath current filter. In short, all the usual measures to avoid ground loops and interference have been taken.
Now it comes: Everything works wonderfully - dead silence. I increase the volume and the music plays pure and clear - hurray! Increase the volume further and BRRRRRRRRMMMMMM - it hums as before. Turned the volume back down to zero, the loud hum persists unchanged. I will spare you a description of what I tried and come to the moment when I gave up:
If I disconnect any speaker plug from one of the two stereo power amplifiers (the whole thing is two-way active with active crossover) the hum disappears on all channels. When I put the speaker plug back in, the hum is back and only disappears when one of the power amplifiers is switched off. Swapping the power amplifiers (left to right and vice versa) makes no difference.
WHAT THE F**K IS THAT?
Thank you for your attention ... 😳
Try another amplifier and preamplifier to check what cause hum.
Cold solder on ground connection may cause this, old capacitors too.
Cold solder on ground connection may cause this, old capacitors too.
