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K3 Line In hum

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Gerard Jendraszkiewicz

K3 Line In hum

Hello,

I wonder if anyone else experienced this type of problem and has a
possible solution ?

Independent of any connectiions I found out a 50Hz hum on my Line-In
audio. After a long investigation I figured out
it was a coupling with other transformers external to the K3. The
transformer of my ampliflier ( 10" away from my K3 ) couples an audible
50hz hum into the Line-In input. It seems the small isolation
transformer in the Line-In line is prone to pickup of
50Hz/60Hz magnetic field. Always I'm able to simulate it with other
transformers.

Increasing the distance from the K3 to the amplifier is not an option as
my shack space is limited. Any sugestions to prevent it?

73 Harry DM5TI

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Jack Smith-6

Re: K3 Line In hum

Same effect can be seen in the output transformers since none of the
K3's transformers are magnetically shielded.

I found 20 to 25 dB difference in induced hum by rotating the K3 in
three dimensions. Whether the hum minimization orientation puts the K3
in a usable position is another question.

Another alternative is to replace the transformers with shielded
versions, assuming space on the PCB is available and a shielded
transformer with the same electrical specifications and footprint is
available.

In my case, the hum field is only (so far) in the basement area of my
workbench.

Jack

Gerard Jendraszkiewicz wrote:

> Hello,
>
> I wonder if anyone else experienced this type of problem and has a
> possible solution ?
>
> Independent of any connectiions I found out a 50Hz hum on my Line-In
> audio. After a long investigation I figured out
> it was a coupling with other transformers external to the K3. The
> transformer of my ampliflier ( 10" away from my K3 ) couples an audible
> 50hz hum into the Line-In input. It seems the small isolation
> transformer in the Line-In line is prone to pickup of
> 50Hz/60Hz magnetic field. Always I'm able to simulate it with other
> transformers.
>
> Increasing the distance from the K3 to the amplifier is not an option as
> my shack space is limited. Any sugestions to prevent it?
>
> 73 Harry DM5TI
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>

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Jim Brown-10

Re: K3 Line In hum

On Tue, 07 Jul 2009 13:13:57 -0400, Jack Smith wrote:

>Another alternative is to replace the transformers with shielded
>versions, assuming space on the PCB is available and a shielded
>transformer with the same electrical specifications and footprint
is
>available.

Or simply eliminate the transformers. They are totally un-necessary
if you do the simple chassis bonding shown in my Ham Interfacing
tutorial.

http://audiosystemsgroup.com/HamInterfacing.pdf

More stuff, in words, in

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

See the chapter on Solving Problems In The Shack.

Another thing to try before digging into the rig. If Elecraft has
followed my recommendation and made TXEQ work on the LineIn, you can
Use TXEQ with maximum cut on the two lower frequency bands. This is
good engineering practice to maximize communications audio quality
anyway, and it should suppress 50/60 Hz by about 20 dB (15dB for the
lowest filter, plus a few more dB from the skirt of the next highest
filter).

This problem with magnetic field susceptibility is well known. My
neighbor, K6XX (who as it happens also works part time as an
engineer for Elecraft) has so much magnetic coupling to his K3 from
a big power supply that it regenerated to 500W when he tried using
the LineIn for RTTY.

73,

Jim Brown K9YC

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Jack Smith-6

Re: K3 Line In hum

Of course if one does not wish to perform surgery on the K3, it would
be possible to set up a 3-dimensional Helmholtz coil around the K3 fed
with 50 or 60 Hz line voltage and adjust the X, Y and Z Helmholtz drive
(level and phase) to null the ambient field at the offending transformer(s).

Jack

Jim Brown wrote:

> On Tue, 07 Jul 2009 13:13:57 -0400, Jack Smith wrote:
>
>
>> Another alternative is to replace the transformers with shielded
>> versions, assuming space on the PCB is available and a shielded
>> transformer with the same electrical specifications and footprint
>>
> is
>
>> available.
>>
>
> Or simply eliminate the transformers. They are totally un-necessary
> if you do the simple chassis bonding shown in my Ham Interfacing
> tutorial.
>
> http://audiosystemsgroup.com/HamInterfacing.pdf
>
> More stuff, in words, in
>
> http://audiosystemsgroup.com/RFI-Ham.pdf
>
> See the chapter on Solving Problems In The Shack.
>
> Another thing to try before digging into the rig. If Elecraft has
> followed my recommendation and made TXEQ work on the LineIn, you can
> Use TXEQ with maximum cut on the two lower frequency bands. This is
> good engineering practice to maximize communications audio quality
> anyway, and it should suppress 50/60 Hz by about 20 dB (15dB for the
> lowest filter, plus a few more dB from the skirt of the next highest
> filter).
>
> This problem with magnetic field susceptibility is well known. My
> neighbor, K6XX (who as it happens also works part time as an
> engineer for Elecraft) has so much magnetic coupling to his K3 from
> a big power supply that it regenerated to 500W when he tried using
> the LineIn for RTTY.
>
> 73,
>
> Jim Brown K9YC
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>

Jim Brown-10

Re: K3 Line In hum

On Tue, 07 Jul 2009 15:39:38 -0400, Jack Smith wrote:

>Of course if one does not wish to perform surgery on the K3, it would
>be possible to set up a 3-dimensional Helmholtz coil around the K3 fed
>with 50 or 60 Hz line voltage and adjust the X, Y and Z Helmholtz drive
>(level and phase) to null the ambient field at the offending transformer(s).

I just love KISS solutions.

73,

Jim K9YC

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Bjorn

Re: K3 Line In hum

In reply to this post by Gerard Jendraszkiewicz

On 7 jul 2009, at 18.53, DM5TI Gerard Jendraszkiewicz wrote:

> I wonder if anyone else experienced this type of problem and has a
> possible solution ?
>
> Independent of any connectiions I found out a 50Hz hum on my Line-In
> audio. After a long investigation I figured out
> it was a coupling with other transformers external to the K3. The
> transformer of my ampliflier ( 10" away from my K3 ) couples an
> audible
> 50hz hum into the Line-In input.

I do have the same problem of my K3 picking up line noise from a SPE
1K-FA amp. Bypassing the input trafos as suggested seems to have
helped some. I also tried the TX equalizer as suggested, but it did
not make a difference in my case.

Another way to reduce the hum is to use the TX noise gate (Config
Menu: TX GATE) which will effectively kill the hum between words. It
won't solve the source of the problem, but it will minimize the effect
of it as most of the line noise is amplified by the compressor between
words. I have set my gate to 10.

73 de Björn,
SM0MDG
SE0X

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