[Elecraft] ferrites for subwoofer: before or after isolation transformers?

[Walter Underwood]

I know you already ran the cables, but twisted pair would probably help.

wunder
K6WRU
Walter Underwood
CM87wj
http://observer.wunderwood.org/ (my blog)

> On May 23, 2020, at 9:37 AM, Nicklas Johnson <nick at n6ol.us> wrote:
> 
> The backstory as briefly as I can make it: I wanted to place my home
> theater subwoofer in the corner of our living room; doing so required
> running two speaker wires and a coaxial cable under the house and plugging
> the subwoofer into a different outlet than the AV receiver; this in turn
> resulted in ground-loop hum (because of a tiny difference in potential
> between the two outlets) which I worked around with a set of 1:1
> low-frequency audio isolation transformers.  The subwoofer is of a type
> that produces a signal based not only on the LFE channel, but also on the
> left and right speaker channels, thus the two speaker wires along with the
> coaxial cable.
> 
> Now the subwoofer is picking up common mode noise on 20m, which isn't
> terribly surprising, as this happens a good bit with consumer-grade
> electronics. I'm hoping to mitigate this with some substantial ferrite
> clamps for all three connections and as many turns as I can get through
> them.
> 
> My hunch is that the best place in the path to clamp them on will be
> immediately before the connection to the speaker itself, on the speaker
> side of the isolation transformer, but I wanted to get the opinions of
> folks who have solved this problem in the past to see if there's any reason
> the ferrites should come before the isolation transformers.
> 
> Thoughts?
> 
>   Nick
> 
> -- 
> *N6OL*
> Saying something doesn't make it true.  Belief in something doesn't make it
> real. And if you have to lie to support a position, that position is not
> worth supporting.
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