Re: K3 & MK2R+ audio hum issue (TOO LONG)

[K5WA]

Jim,

 

I am going through the same struggle with my K3s, MK2R and Heil ProSet.  I
didn't have as much hum as I did a hollow echo effect (RF feedback?), so I
hope this addresses your issues.  I have spent an incredible amount of time
trying to figure out the problems and there are many.  I don't know why
microHAM doesn't have suggested base configurations that would apply to all
implementations, but they don't.  They also have never heard of the "a
picture is worth a thousand words" phrase because their manual uses LOTS of
words and many of them add to the confusion by not indicating whether they
are referring to the sound card, MK2R or rig inputs and outputs.  Many of
the manual's sentences can be misinterpreted.  The manual was not written
with "ease of use" in mind and you are referred to "outside experts" to get
a complete history of ground loops rather than tucking a few "good
practices" into the manual.

 

Anyway, after trying suggestions from several sources, the ones that made
the most difference for me and ALMOST (I'm so close) have me running are
these:

 

1)       Use a separate ISOLATED power supply for each rig as well as the
MK2R.  I had been using a common power supply when I first started this
adventure.  I had to unsolder the AC line cord ground connection from inside
my Astron 35 amp supply and my MFJ 25A switching supply to let the 12VDC
float.  I am currently using my test bench isolated power supply to power
the MK2R during this setup phase and will have to acquire another isolated
supply when I move things off the test bench.

2)       Insert ground loop breakers in the receive audio lines (The DIN
plug line on the back of the MK2R that goes to each K3 headphone jack).  I
used some that I purchased from Radio Shack, but I'm sure a competent person
could build their own given enough time.

3)       Only use the FRONT panel headphone jack!  It makes a big difference
whether you use the rear headphone jack or the front panel jack for the
MK2R.  I had bad feedback when I plugged into the rear headphone jack and it
was greatly reduced when I used the front panel jack.

4)       Get a bunch of ferrite torroids and wrap everything!  Mic line,
power supply lines, headphone lines.

 

I'm getting very close to being able to take this setup to my contest
station and putting it on the air with big antennas and amplifiers.  My home
test station is a terrible RF hole (second floor room, no proper ground,
antennas in attic over head, etc.) so if I can get it running here, I
believe I'll be in good shape when I take this setup to my contest station
where conditions are much better.

 

Bottom line, I am not deeply steeped in the engineering arts and don't have
enough time to endlessly dig into the "pin 1" problem.  I am an admitted
appliance operator who just likes to enjoy operating with minor excursions
into a deeper understanding of theory when it moves up my priority scale.  I
don't completely understand why the above suggestions worked for me, but
they did.  Hopefully, my bullet points above can get you going with these 4
steps while others can pontificate about why it worked.  I'm just glad
Elecraft didn't make me study a DSP engineering manual before I turned on my
K3s.  ;-)

 

Bob K5WA

K3 #234 and #752

K2 #4687

 

>>>>>>>>>>>>>>>>>

Message: 8

Date: Sat, 30 Aug 2008 17:26:43 -0500

From: "Jim Harvey" <[hidden email]>

Subject: [Elecraft] K3 & MK2R+ audio hum issue

To: <[hidden email]>

Message-ID: <004901c90aef$7b42b2c0$6a00a8c0@jimpc>

Content-Type: text/plain; charset="us-ascii"

 

I just received my K3 yesterday and have it interfaced to my Microham MK2R+.

CW operation is perfect but I have some audio hum and distortion in the

monitor on SSB. I'm using a Heil Proset connected to the MK2R+. Joe, W4TV,

has given me some good suggestions but the problem is still there. Is there

anyone else using this combination that can help?

 

 

 

Jim N0AV

 

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[Jim Brown-10]

On Sun, 31 Aug 2008 09:32:51 -0500, Bob Evans wrote:

>The manual was not written with "ease of use" in mind and you are
>referred to "outside experts" to get a complete history of ground
>loops rather than tucking a few "good practices" into the manual.

I don't know anything specific about the MK2R, but many (most?) ham
and computer audio products are built with very WRONG grounding
practices. Indeed, most ham transceivers, including the K3, do some or
all of this stuff wrong!  

There's a lot of VERY wrong thinking about hum, buzz, and ground
loops, and that has led many folks to some really dumb practices that
often CAUSE problems rather than solving them (and that are often a
lot more expensive than solving the real problem).

To understand what's REALLY going on with so-called "ground loops"
(and some VERY low cost solutions), have a look at

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

and

http://audiosystemsgroup.com/HamInterfacing.pdf

73,

Jim Brown K9YC


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