subwoofer hum

Archived from groups: rec.audio.tech (More info?)

In article <a6aaf71f.0410201702.51288c36@posting.google.com>, jts
<sanders_family1@comcast.net> wrote:

> I have a subwoofer that hums when it is connected to my A/V amplifier.
> Both unitw were repaired recently, yet the problem persists. I am at
> a loss. The solid state amplifiers were replaced in the Pioneer
> SA-HE200 amplifier. Only the powered subwoofer is effected; the other
> speakers (front, satellite, center) function well. The amplifier in
> the powered subwoofer was just replaced as well. I installed the unit
> myself and hooked it up as KLH instructed. The subwoofer is an E-10D,
> part of the plat-6 system. The interconnect cable is shielded and
> uses gold plated RCA connectors. The problem is the same with the
> unshielded cable delivered with the speakers. What do I try next?
> BTW, music does play through the subwoofer, but the hum is louder. I
> can also change the hum volume by playing with the subwoofer gain.

1. Does the subwoofer hum when there is no cable attached to it?
This will help localize if the problem is in the subwoofer itself,
or if it is picking up the noise from the receiver.

2. Try playing with the power cord. Flip the plug 180 degrees if
it will allow. Also, try plugging the subwoofer and receiver into
the same outlet (or same power strip). Try a different outlet,
different circuit, and try flipping the plug on the receiver. You
might have a noisey circuit, bad ground, mis-wired outlet, or a
ground loop.

-john-

--
====================================================================
John A. Weeks III 952-432-2708 john@johnweeks.com
Newave Communications http://www.johnweeks.com
====================================================================

Archived from groups: rec.audio.tech (More info?)

>
> You have a cable telly connection don't you?

Yes.

>
> If yes, this is a not exactly unknown problem, get a isolating transformer
> for the cable telly connection, problem (most likely) solved.
>
> The problem is a ground loop caused by the mains ground being at a different
> potential to the ground connection used by the cable TV connection. As the
> rest of your system, most likely has 2 core mains leads it does not hum.
> The subwoofer (I am betting) has a 3 core mains lead and the earth
> connection here allows loop current to flow thru the screens of the audio
> cables giving rise to your hum.

It's after 10PM here, and I can't get an isolation tranformer tonight.
It did occur to me that I used to plug the subwoofer directly into
the wall outlet. Yesterday I plugged it into an outlet in the power
strip labelled "transformer". The television is also plugged into
another transformer outlet. When I moved the subwoofer to a
non-transformer recepticle on the same power strip, the hum
disappeared. Your suggestion made me think about how I might alter
the circuit to reduce the ground loop interference, and it worked.
Thanks, Dan.

Jack