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I sold an Infinity SSW-210 powered subwoofer. It is a mono unit with two line level inputs, a plate amp, and two 10" woofers. I have a 30-day warranty policy, and it came back with low-level hum that was not obvious in my somewhat noisy environment. My customer has a quiet environment and the sub sits on a wooden floor; the hum couples into the floor and is annoying to the customer.
When turned on with the volume all the way down there is a slight hum that I can only hear with my ear near the woofers. The volume of the hum increases slightly with increasing volume. The obvious thing to suspect is cables, so I borrowed a pair of RCA shorting plugs from the phono inputs of a receiver and stuck them in the sub's inputs. No change whatsoever, so it isn't the cables; the problem, if there is one, must be internal.
Note that this is 60 cycle hum, not 120 cycle hum. The sub operates properly otherwise, and is a pretty darn good sub.
We examined the amp; there are no obvious problems. The caps all look good, etc.
So the question is whether low level hum is unavoidable or addressable. My technician thinks it's radiation from the toroidal transformer or from the ac leads from the transformer to the power supply.
Anyone out there with experience on low-level hum on decent-quality powered subs?
Follow Ups:
The problem is common to Cable TV subscribers. The problem is a "ground-loop".
Resolve this by making a simple Ground-loop isolator, using 2 75 to 300 Ohm cable adaptors connected back to back. or by purchasing from local Store.
-Try grounding the cable splitter to the screw holding the A/C wall plate, if any of these make a slight difference, contact the cable provider and reques..,make that "DEMAND" that they install a ($70) GLI (Ground Loop Isolator).
-Try to avoid, inexpensive Power surge bars, as all components connected to it share a small ground.
Connect the Sub-Woofer to a separate wall plug if possible.
It turned out just opening it up and tightly twisting the leads from the power transformer to the board solved 95% of the problem. Proper grounding was the other few percent.
Ah, quiet!
Wow,
I'm glad to see somebody finally got to 'root' on one of these wacky hum/ground loop problems.
Congrats::
Too much is never enough
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