Ariston Audio RD11s : electrical hum when off

[davstev]

Depends on which way the two prong power plug is plugged into the power bar. One way, the hum is there when the motor is ON (so there when music is playing - very BAD!), or when the motor is turned OFF (which wasn't too bad on the TD160, but it bugged me on the 145, as it would come on with the auto-shut off, and I was hoping to use it in the bedroom system, but the hum would bug me if I was falling asleep - I know, FIRST WORLD PROBLEMS!).

Surprised that you could hear the hum over the sound of the working motor, that's really something. The hum that I am referring to is very very minor, you have to have your ear beside the plinth to hear it, when the motor's off, when I think you should hear nothing. This is what you'd hear in your bedroom- when powered off? I hesistate to think that mine's loud enough to hear from a distance...

 

[ripblade]

My AA RD11s- also "*very* subtle and completely inaudible" as you say, in the off position. It just strikes me as odd, that's all. I assume that this kind of unit, when off, it's passing no electricity through it, which maybe isn't the case, and seems mildly worrying.

I find it midly troubling as well, but I wouldn't worry about it. Mine's been doing it for the dozen years since I bought it and the pulley's not even warm to the touch. The reason for it is befuddling but my best wild guess is that AC current is flowing through* the power switch's snubbing capacitor. Caps block DC but are frequency dependent with AC, so it's not impossible. In any case, it's not enough current to turn the motor, or even warm the windings, but it is enough to build a magnetic field within them, which is what's causing the vibration as the field builds and collapses at the line frequency.

*Technically, not through but around the capacitor. But let's not confuse matters lol.

 

[doctor fuse]

Surprised that you could hear the hum over the sound of the working motor, that's really something. The hum that I am referring to is very very minor, you have to have your ear beside the plinth to hear it, when the motor's off, when I think you should hear nothing. This is what you'd hear in your bedroom- when powered off? I hesistate to think that mine's loud enough to hear from a distance...

No, mine isn't the mechanical motor noise, it is a *very faint* electrical hum. I sometimes like to play loud music as I fall asleep (it's rare, but sometimes; my girlfriend and I have the luxury of having separate places), and when it's loud, I find the hum annoying, especially when i am just in the first stages of nodding off.

 

[tnsilver]

my best wild guess is that AC current is flowing through* the power switch's snubbing capacitor.

That's exactly what happens but it shouldn't ever. It happens when either the snubber capacitor across the power switch poles is faulty, or it's capacitance value is too large and it allows current to flow when the switch is open. It should be a 10nf (0.01µF), across-the-line safety capacitor (class X2) and it's easier swapped out for a new replacement than measured live in series for current leaks.

The other poster with the Thorens hum problem appears to have a grounding issue, that's unrelated to the Ariston problem.

 

[ripblade]

Sounds reasonable to me. A smaller value would reduce the current further but might not be as effective at suppressing the popping noise. A simpler solution might be to install a 2nd power switch without a snubber on the back of the plinth. Equivalent to unplugging the deck without having to bend down, it could be switched on at the beginning of a listening session and switch off at the end till the next one. Alternately, a switched power bar could be used.