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

[Nicklas Johnson]

Happy to report that the subwoofer problem got about 95% better with the
placement of ferrites immediately before the subwoofer on the power cord,
the LFE channel and the speaker channels.  It still picks up just a tiny
bit of 20m racket even with nothing connected to it, which I suspect could
be a consequence of the speaker coil picking up the signal and getting
rectified in the subwoofer's amplifier.  I think it would be difficult to
mitigate without more effort than the very small amount of sound is worth.
(I'd probably have to disassemble the subwoofer and add a new cable
between the amplifier and the speaker that took a bunch of turns through a
ferrite ring... something I'm not willing to do yet.)

(The question about the isolation transformers came up because the
subwoofer must necessarily plug into a different outlet than the receiver
due to its placement, and the answer is to add the ferrite as close to the
amplifier as possible, on both ends, so necessarily after the isolation
transformers, right up against the subwoofer is the place to go.)

Adding ferrite to all the speaker wires, the LFE channel, and the power
cord at the receiver as Dave (NK7Z) suggested got rid of the small
amount of noise that was being picked up on other channels, so I'd call
that piece a total success.  Because of the way our AV cabinet is arranged,
I needed the ferrites to be a little bit closer to the wall than to the
receiver, so I gave the wire leading to the receiver several twists on its
way for those last few feet.

In all cases I was able to get at least 7 turns through the clamps I
bought... they were pretty good hefty sizes.

Incidentally, Mouser has very good prices and reasonably priced shipping on
Fair-Ride material 31 clamp-ons, and it pays to buy in bulk-- 10 costs the
same as 7.  They also vacuum-seal and bubble-wrap the hell out of it so it
arrives intact.

Leaving this message so it's searchable by the next person.  As always, I
appreciate all the help and suggestions from everyone.

   Nick

On Sat, 23 May 2020 at 17:01, Nicklas Johnson  wrote:

> I certainly agree.  And of course there's no "one size fits all" for RFI
> problems.  I think it's somewhat likely I have multiple problems going on
> here too; I noticed, for example, that even when it's completely
> disconnected from all its audio inputs, I can still hear a little racket on
> the sub; it may need a hefty ferrite on the power cord, or I suppose it's
> always possible it's picking up 20m from the speaker coil, then rectifying
> that.  I won't know until I get some appropriate ferrites delivered to test
> out (mid-week).
>
> Sadly, it seems like most consumer-grade audio equipment is optimized more
> for cost than for design quality and RFI suppression, even equipment that's
> supposed to be "high-end."  And then sometimes you can buy a piece of cheap
> gear and it rejects RF better than high-end stuff.  Kind of a crap shoot.
>
> I appreciate all the suggestions and pointers.  In the absolute worst
> case, I can always play on another band when my better half wants to watch
> a movie or play a game, too.
>
>Nick
>
>
> On Sat, 23 May 2020 at 16:39, Dave Cole  wrote:
>
>> All of Jim's material is like gold for RFI suppression.
>>
>> 73, and thanks,
>> Dave (NK7Z)
>> https://www.nk7z.net
>> ARRL Volunteer Examiner
>> ARRL Technical Specialist
>> ARRL Asst. Director, NW Division, Technical Resources
>>
>> On 5/23/20 2:02 PM, Nicklas Johnson wrote:
>> > Thanks, Dave.  A very good point about the amp picking up stray RF off
>> > the cable and returning it as audio; I'll be sure to clamp down on both
>> > ends.
>> >
>> > It's definitely not a new problem, and I've used Jim's recommendations
>> > to much success in the past.  In fact, I referenced it again today
>> > because I couldn't remember which mix of Fair-Rite was the right one.
>> >
>> > Nick
>> >
>> > On Sat, 23 May 2020 at 10:58, Dave Cole > > > wrote:
>> >
>> > I would put the ferrite material as close to the speaker as
>> possible,
>> > and as close as possible to the amp...
>> >
>> > It is important you also protect the amp from stray RF.  If the
>> speaker
>> > cable is picking up RF, and feeding it back into the audio amp
>> output
>> > stage, you can get rectification within that stage in the amp, thus
>> > feeding actual audio, (not RF), back down the speaker cable into the
>> > speaker(s), and then you start hearing things on the speaker(s).
>> >
>> > I had a ham friend living 700 or 800 feet from me-- when he lit off
>> his
>> > KW, I would hear SSB in the speakers, even with the amp off, and
>> > unplugged.  This was happening via the method above.
>> >
>> > See Jim's paper on quieting things down:
>> >
>> > http://www.audiosystemsgroup.com/RFI-Ham.pdf
>> >
>> > 73, and thanks,
>> > Dave (NK7Z)
>> > https://www.nk7z.net
>> > ARRL Volunteer Examiner
>> > ARRL Technical Specialist
>> >

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

[Jim Brown]

On 5/23/2020 5:01 PM, Nicklas Johnson wrote:

Sadly, it seems like most consumer-grade audio equipment is optimized more
for cost than for design quality and RFI suppression, even equipment that's
supposed to be "high-end."  And then sometimes you can buy a piece of cheap
gear and it rejects RF better than high-end stuff.  Kind of a crap shoot.


For more than 30 years, virtually ALL electronics has been built with 
Pin One Problems. This has as much to do with stupid as it does with 
cheap. When Neil Muncy, ex-W3WJE, now SK, first exposed it in 1994, 
virtually all Pro equipment had Pin One Problems. Every ham rig I 
studied the last time I was in Dayton and last year in Visalia had Pin 
One Problems, including Elecraft.


THAT'S the major reason we need ferrite chokes on all the "receiving 
antennas."  It's also a major mechanism coupling for RF noise OUT of the 
box. The Pin One Problem occurs with the AC "Green Wire" (Equipment 
Ground) and with antenna jacks in home entertainment systems AND in CATV 
and DSL systems. They all put noise on the coax shield and the Green Wire.


73, Jim K9YC
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Re: [Elecraft] ferrites for subwoofer: before or after isolation transformers?

[Nicklas Johnson]

I certainly agree.  And of course there's no "one size fits all" for RFI
problems.  I think it's somewhat likely I have multiple problems going on
here too; I noticed, for example, that even when it's completely
disconnected from all its audio inputs, I can still hear a little racket on
the sub; it may need a hefty ferrite on the power cord, or I suppose it's
always possible it's picking up 20m from the speaker coil, then rectifying
that.  I won't know until I get some appropriate ferrites delivered to test
out (mid-week).

Sadly, it seems like most consumer-grade audio equipment is optimized more
for cost than for design quality and RFI suppression, even equipment that's
supposed to be "high-end."  And then sometimes you can buy a piece of cheap
gear and it rejects RF better than high-end stuff.  Kind of a crap shoot.

I appreciate all the suggestions and pointers.  In the absolute worst case,
I can always play on another band when my better half wants to watch a
movie or play a game, too.

   Nick


On Sat, 23 May 2020 at 16:39, Dave Cole  wrote:

> All of Jim's material is like gold for RFI suppression.
>
> 73, and thanks,
> Dave (NK7Z)
> https://www.nk7z.net
> ARRL Volunteer Examiner
> ARRL Technical Specialist
> ARRL Asst. Director, NW Division, Technical Resources
>
> On 5/23/20 2:02 PM, Nicklas Johnson wrote:
> > Thanks, Dave.  A very good point about the amp picking up stray RF off
> > the cable and returning it as audio; I'll be sure to clamp down on both
> > ends.
> >
> > It's definitely not a new problem, and I've used Jim's recommendations
> > to much success in the past.  In fact, I referenced it again today
> > because I couldn't remember which mix of Fair-Rite was the right one.
> >
> > Nick
> >
> > On Sat, 23 May 2020 at 10:58, Dave Cole  > > wrote:
> >
> > I would put the ferrite material as close to the speaker as possible,
> > and as close as possible to the amp...
> >
> > It is important you also protect the amp from stray RF.  If the
> speaker
> > cable is picking up RF, and feeding it back into the audio amp output
> > stage, you can get rectification within that stage in the amp, thus
> > feeding actual audio, (not RF), back down the speaker cable into the
> > speaker(s), and then you start hearing things on the speaker(s).
> >
> > I had a ham friend living 700 or 800 feet from me-- when he lit off
> his
> > KW, I would hear SSB in the speakers, even with the amp off, and
> > unplugged.  This was happening via the method above.
> >
> > See Jim's paper on quieting things down:
> >
> > http://www.audiosystemsgroup.com/RFI-Ham.pdf
> >
> > 73, and thanks,
> > Dave (NK7Z)
> > https://www.nk7z.net
> > ARRL Volunteer Examiner
> > ARRL Technical Specialist
> > ARRL Asst. Director, NW Division, Technical Resources
> >
> > On 5/23/20 10:19 AM, Nicklas Johnson wrote:
> >  > I've got a set of these on the way, as well as a handful of their
> > next two
> >  > smaller siblings, just because I like to have a variety in my
> > desk for
> >  > various applications:
> >  >
> https://www.fair-rite.com/product/round-cable-snap-its-2631181381/
> >  >
> >  > Given the arrangement at the subwoofer of
> wall-connection-->isolation
> >  > transformers-->subwoofer, would you put the ferrite right before
> the
> >  > subwoofer then?
> >  >
> >  > I didn't think about adding one at the amp; though I haven't had
> > problems
> >  > with any common mode noise getting into the amp from the other
> > speakers in
> >  > the room, I can't be sure about the LFE coaxial cable, so that
> > wouldn't
> >  > hurt.
> >  >
> >  > Nick
> >  >
> >  >
> >  > On Sat, 23 May 2020 at 10:08, Dave Cole  > > wrote:
> >  >
> >  >> Grab some FT-240/31 ferrites from Fair-Rite, (these are the large
> >  >> rings), and put seven or eight turns of speaker cable through
> each,
> >  >> tight wound.  Add one at the speaker, and one at the amp.
> >  >>
> >  >> 73, and thanks,
> >  >> Dave (NK7Z)
> >  >> https://www.nk7z.net
> >  >> ARRL Volunteer Examiner
> >  >> ARRL Technical Specialist
> >  >> ARRL Asst. Director, NW Division, Technical Resources
> >  >>
> >  >> On 5/23/20 9:37 AM, Nicklas Johnson 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 

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

[Dave Cole]

All of Jim's material is like gold for RFI suppression.

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources

On 5/23/20 2:02 PM, Nicklas Johnson wrote:
Thanks, Dave.  A very good point about the amp picking up stray RF off 
the cable and returning it as audio; I'll be sure to clamp down on both 
ends.


It's definitely not a new problem, and I've used Jim's recommendations 
to much success in the past.  In fact, I referenced it again today 
because I couldn't remember which mix of Fair-Rite was the right one.


    Nick

On Sat, 23 May 2020 at 10:58, Dave Cole > wrote:


I would put the ferrite material as close to the speaker as possible,
and as close as possible to the amp...

It is important you also protect the amp from stray RF.  If the speaker
cable is picking up RF, and feeding it back into the audio amp output
stage, you can get rectification within that stage in the amp, thus
feeding actual audio, (not RF), back down the speaker cable into the
speaker(s), and then you start hearing things on the speaker(s).

I had a ham friend living 700 or 800 feet from me-- when he lit off his
KW, I would hear SSB in the speakers, even with the amp off, and
unplugged.  This was happening via the method above.

See Jim's paper on quieting things down:

http://www.audiosystemsgroup.com/RFI-Ham.pdf

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources

On 5/23/20 10:19 AM, Nicklas Johnson wrote:
 > I've got a set of these on the way, as well as a handful of their
next two
 > smaller siblings, just because I like to have a variety in my
desk for
 > various applications:
 > https://www.fair-rite.com/product/round-cable-snap-its-2631181381/
 >
 > Given the arrangement at the subwoofer of wall-connection-->isolation
 > transformers-->subwoofer, would you put the ferrite right before the
 > subwoofer then?
 >
 > I didn't think about adding one at the amp; though I haven't had
problems
 > with any common mode noise getting into the amp from the other
speakers in
 > the room, I can't be sure about the LFE coaxial cable, so that
wouldn't
 > hurt.
 >
 >     Nick
 >
 >
 > On Sat, 23 May 2020 at 10:08, Dave Cole mailto:d...@nk7z.net>> wrote:
 >
 >> Grab some FT-240/31 ferrites from Fair-Rite, (these are the large
 >> rings), and put seven or eight turns of speaker cable through each,
 >> tight wound.  Add one at the speaker, and one at the amp.
 >>
 >> 73, and thanks,
 >> Dave (NK7Z)
 >> https://www.nk7z.net
 >> ARRL Volunteer Examiner
 >> ARRL Technical Specialist
 >> ARRL Asst. Director, NW Division, Technical Resources
 >>
 >> On 5/23/20 9:37 AM, Nicklas Johnson 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
 >>>
 >> __
 >> Elecraft mailing list
 >> Home: http://mailman.qth.net/mailman/listinfo/elecraft
 >> Help: http://mailman.qth.net/mmfaq.htm
 >> Post: mailto:Elecraft@mailman.qth.net

 >>
 >> This 

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

[Nicklas Johnson]

Thanks, Dave.  A very good point about the amp picking up stray RF off the
cable and returning it as audio; I'll be sure to clamp down on both ends.

It's definitely not a new problem, and I've used Jim's recommendations to
much success in the past.  In fact, I referenced it again today because I
couldn't remember which mix of Fair-Rite was the right one.

   Nick

On Sat, 23 May 2020 at 10:58, Dave Cole  wrote:

> I would put the ferrite material as close to the speaker as possible,
> and as close as possible to the amp...
>
> It is important you also protect the amp from stray RF.  If the speaker
> cable is picking up RF, and feeding it back into the audio amp output
> stage, you can get rectification within that stage in the amp, thus
> feeding actual audio, (not RF), back down the speaker cable into the
> speaker(s), and then you start hearing things on the speaker(s).
>
> I had a ham friend living 700 or 800 feet from me-- when he lit off his
> KW, I would hear SSB in the speakers, even with the amp off, and
> unplugged.  This was happening via the method above.
>
> See Jim's paper on quieting things down:
>
> http://www.audiosystemsgroup.com/RFI-Ham.pdf
>
> 73, and thanks,
> Dave (NK7Z)
> https://www.nk7z.net
> ARRL Volunteer Examiner
> ARRL Technical Specialist
> ARRL Asst. Director, NW Division, Technical Resources
>
> On 5/23/20 10:19 AM, Nicklas Johnson wrote:
> > I've got a set of these on the way, as well as a handful of their next
> two
> > smaller siblings, just because I like to have a variety in my desk for
> > various applications:
> > https://www.fair-rite.com/product/round-cable-snap-its-2631181381/
> >
> > Given the arrangement at the subwoofer of wall-connection-->isolation
> > transformers-->subwoofer, would you put the ferrite right before the
> > subwoofer then?
> >
> > I didn't think about adding one at the amp; though I haven't had problems
> > with any common mode noise getting into the amp from the other speakers
> in
> > the room, I can't be sure about the LFE coaxial cable, so that wouldn't
> > hurt.
> >
> > Nick
> >
> >
> > On Sat, 23 May 2020 at 10:08, Dave Cole  wrote:
> >
> >> Grab some FT-240/31 ferrites from Fair-Rite, (these are the large
> >> rings), and put seven or eight turns of speaker cable through each,
> >> tight wound.  Add one at the speaker, and one at the amp.
> >>
> >> 73, and thanks,
> >> Dave (NK7Z)
> >> https://www.nk7z.net
> >> ARRL Volunteer Examiner
> >> ARRL Technical Specialist
> >> ARRL Asst. Director, NW Division, Technical Resources
> >>
> >> On 5/23/20 9:37 AM, Nicklas Johnson 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
> >>>
> >> __
> >> Elecraft mailing list
> >> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> >> Help: http://mailman.qth.net/mmfaq.htm
> >> Post: mailto:Elecraft@mailman.qth.net
> >>
> >> This list hosted by: http://www.qsl.net
> >> Please help support this email list: http://www.qsl.net/donate.html
> >> Message delivered to n...@n6ol.us
> >>
> >
> >
> __
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft@mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to n...@n6ol.us
>


-- 
*N6OL*
Saying something doesn't make it true.  Belief in something doesn't make it
real. And if you have 

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

[Jim Brown]

On 5/23/2020 9:37 AM, Nicklas Johnson 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 


NOT "ground loop hum"  but "buzz," which is triplen harmonics of 60 Hz 
-- 180 Hz, 360, 540, etc..

(because of a tiny difference in potential

Yes, but it's a difference in potential of the green wires.

The solution -- run AC for the subwoofer from same outlet that powers 
the receiver.



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. 


Consumer electronics is notorious for this problem.

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.


What three connections are we talking about here? Is it speaker cable or 
unbalanced audio coax? If speaker cable, replace with twisted pair, 
which can be built from two colors of ordinary THHN house wire. Spool 
out lengths of the two colors, put one end in a vise (or equivalent), 
the other end in a drill, and slowly twist a lot. When you've twisted 
more that you think is needed, lay the drill down overnight to let the 
cable develop some memory. When you do remove it from the drill, it will 
untwist some. That's why it's best to twist it a lot.


Chokes as Dave recommended should be applied individually to each audio 
cable and the AC cables for both the receiver and the sub-woofer.


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.


If you have run AC as I've recommended, the transformers are probably 
not needed.


73, Jim K9YC
__
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Re: [Elecraft] ferrites for subwoofer: before or after isolation transformers?

[Dave Cole]

I would put the ferrite material as close to the speaker as possible, 
and as close as possible to the amp...


It is important you also protect the amp from stray RF.  If the speaker 
cable is picking up RF, and feeding it back into the audio amp output 
stage, you can get rectification within that stage in the amp, thus 
feeding actual audio, (not RF), back down the speaker cable into the 
speaker(s), and then you start hearing things on the speaker(s).


I had a ham friend living 700 or 800 feet from me-- when he lit off his 
KW, I would hear SSB in the speakers, even with the amp off, and 
unplugged.  This was happening via the method above.


See Jim's paper on quieting things down:

http://www.audiosystemsgroup.com/RFI-Ham.pdf

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources

On 5/23/20 10:19 AM, Nicklas Johnson wrote:

I've got a set of these on the way, as well as a handful of their next two
smaller siblings, just because I like to have a variety in my desk for
various applications:
https://www.fair-rite.com/product/round-cable-snap-its-2631181381/

Given the arrangement at the subwoofer of wall-connection-->isolation
transformers-->subwoofer, would you put the ferrite right before the
subwoofer then?

I didn't think about adding one at the amp; though I haven't had problems
with any common mode noise getting into the amp from the other speakers in
the room, I can't be sure about the LFE coaxial cable, so that wouldn't
hurt.

Nick


On Sat, 23 May 2020 at 10:08, Dave Cole  wrote:


Grab some FT-240/31 ferrites from Fair-Rite, (these are the large
rings), and put seven or eight turns of speaker cable through each,
tight wound.  Add one at the speaker, and one at the amp.

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources

On 5/23/20 9:37 AM, Nicklas Johnson 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


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

[Nicklas Johnson]

I've got a set of these on the way, as well as a handful of their next two
smaller siblings, just because I like to have a variety in my desk for
various applications:
https://www.fair-rite.com/product/round-cable-snap-its-2631181381/

Given the arrangement at the subwoofer of wall-connection-->isolation
transformers-->subwoofer, would you put the ferrite right before the
subwoofer then?

I didn't think about adding one at the amp; though I haven't had problems
with any common mode noise getting into the amp from the other speakers in
the room, I can't be sure about the LFE coaxial cable, so that wouldn't
hurt.

   Nick


On Sat, 23 May 2020 at 10:08, Dave Cole  wrote:

> Grab some FT-240/31 ferrites from Fair-Rite, (these are the large
> rings), and put seven or eight turns of speaker cable through each,
> tight wound.  Add one at the speaker, and one at the amp.
>
> 73, and thanks,
> Dave (NK7Z)
> https://www.nk7z.net
> ARRL Volunteer Examiner
> ARRL Technical Specialist
> ARRL Asst. Director, NW Division, Technical Resources
>
> On 5/23/20 9:37 AM, Nicklas Johnson 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
> >
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>


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

[Peter Dougherty]

I'm experiencing something similar. I have my sub-2 output connected to bass
shakers on my sofa, and the wiring picks up an incredible amount of RF on
20. As my wife found out when she was taking a nap in the room while I was
contesting. As soon as I switched to 20 she was getting rumbled to the
pattern of CQ TEST. That was an interesting conversation, and something I
will look at this summer.

As for your low frequencies getting into your left and right main, why not
switch them to "small" in the AVR menu, and let the sub do all the work
below 80 Hz?

I have had some luck putting ferrites just before the speaker terminals in
the past. I sadly cut all my speaker cable to length so there's no room to
wind around a core, so these will need to be clamp-ons for me. I get into my
center and surrounds on 40 and 20.

Or I can tell my XYL to nap in the living room, since there's just the two
of us in the house.

 - pjd

-Original Message-
From: elecraft-boun...@mailman.qth.net  On
Behalf Of Nicklas Johnson
Sent: Saturday, May 23, 2020 12:38 PM
To: elecraft 
Subject: [Elecraft] ferrites for subwoofer: before or after isolation
transformers?

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

[Dave Cole]

Grab some FT-240/31 ferrites from Fair-Rite, (these are the large 
rings), and put seven or eight turns of speaker cable through each, 
tight wound.  Add one at the speaker, and one at the amp.


73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources

On 5/23/20 9:37 AM, Nicklas Johnson 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


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

[Nicklas Johnson]

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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