K2 SSB audio problem

[George Winship, NC5G]

After 11 years of operating and many unsolicited reports of great audio, I am suddenly getting not so good reports from my K2/100. Present setup is K2/100, KAT100, KPA500, and resonant antennas on 75 and 40 meters. Very rarely do SSB on any other bands. Stations seem to have trouble describing the problem. Reports vary from fuzziness, distortion, to clipping. I bypassed the tuner and amp, hooking feed line directly to K2/100 and also turned the power down to ten watts to shut off the KPA100 and problem persists. No difference between MH2 and CM500 mics. These test were done with stations who know my rig and my voice. This is an early K2/100. All mods were done years ago to K2, SSB, and KPA100. Receive audio is unchanged. Visual inspection of boards look OK.

As a further check, I connected my KX3 to amp and antennas with great results.

Any suggestions?

Thanks es 73,

George, NC5G

[Don Wilhelm-4]

George,

Ask yourself what has changed between good operation and now.
Have you re-arranged your shack?  The K2 is sensitive to devices with
transformers positioned within 2 feet of the left side panel - the
transformer's magnetic field modulates the K2 VFO.

As a test, move your K2 away from everything else on the desk and run a
test.

If this proves to be your problem, you can install the optional mod kit,
VCOSHLDKT.

73,
Don W3FPR


On 10/21/2012 10:48 PM, George Winship, NC5G wrote:

> After 11 years of operating and many unsolicited reports of great audio, I am
> suddenly getting not so good reports from my K2/100. Present setup is
> K2/100, KAT100, KPA500, and resonant antennas on 75 and 40 meters. Very
> rarely do SSB on any other bands. Stations seem to have trouble describing
> the problem. Reports vary from fuzziness, distortion, to clipping. I
> bypassed the tuner and amp, hooking feed line directly to K2/100 and also
> turned the power down to ten watts to shut off the KPA100 and problem
> persists. No difference between MH2 and CM500 mics. These test were done
> with stations who know my rig and my voice. This is an early K2/100. All
> mods were done years ago to K2, SSB, and KPA100. Receive audio is unchanged.
> Visual inspection of boards look OK.
>
> As a further check, I connected my KX3 to amp and antennas with great
> results.
>

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[KD4NUE]

FETS in low power amplifier?

David
KD4NUE

Sent from my Verizon Wireless Phone

----- Reply message -----
From: "George Winship, NC5G" <[hidden email]>
Date: Sun, Oct 21, 2012 22:48
Subject: [Elecraft] K2 SSB audio problem
To: <[hidden email]>

After 11 years of operating and many unsolicited reports of great audio, I am
suddenly getting not so good reports from my K2/100. Present setup is
K2/100, KAT100, KPA500, and resonant antennas on 75 and 40 meters. Very
rarely do SSB on any other bands. Stations seem to have trouble describing
the problem. Reports vary from fuzziness, distortion, to clipping. I
bypassed the tuner and amp, hooking feed line directly to K2/100 and also
turned the power down to ten watts to shut off the KPA100 and problem
persists. No difference between MH2 and CM500 mics. These test were done
with stations who know my rig and my voice. This is an early K2/100. All
mods were done years ago to K2, SSB, and KPA100. Receive audio is unchanged.
Visual inspection of boards look OK.

As a further check, I connected my KX3 to amp and antennas with great
results.

Any suggestions?

Thanks es 73,

George, NC5G





--
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[VK1OO, Mike Walkington]

Hi George,

I have a similar set-up, having added the KPA500 two or so weeks ago.
Recently a local ham using an SDR as a spectrum analyser notied that I have a lot of splatter on my signal.
The KPA500 is locted about 8 inches above the K2 and KPA100. I have not fittted the VCO Shield.  Thanks to your email I now have another possible cause to investigate.

[Vic Rosenthal]

My experience with the K2 and the much smaller transformer in an antenna rotor control
lead me to believe that it is very likely that the big transformer in the KPA500 is
"FM-ing" your K2. The VCO shield kit is likely to solve this problem.

On 10/22/2012 3:53 AM, VK1OO, Mike Walkington wrote:

> Hi George,
>
> I have a similar set-up, having added the KPA500 two or so weeks ago.
> Recently a local ham using an SDR as a spectrum analyser notied that I have
> a lot of splatter on my signal.
> The KPA500 is locted about 8 inches above the K2 and KPA100. I have not
> fittted the VCO Shield.  Thanks to your email I now have another possible
> cause to investigate.
>
>
>
>
>
>
> -----
>
>
> Cheers
> Mike
> VK1OO (ex AC7MZ, VK1KCK)
> K2: 2599
>

--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/

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[George Winship, NC5G]

You are probably right, Vic. Per Don's suggestions, I will do some more tests, but it will probably be this weekend before I get to play radio again. I will post what I find out.

73, George, NC5G

<quote author="Vic, K2VCO">
My experience with the K2 and the much smaller transformer in an antenna rotor control
lead me to believe that it is very likely that the big transformer in the KPA500 is
"FM-ing" your K2. The VCO shield kit is likely to solve this problem.

[George Winship, NC5G]

After some extensive on the air testing with my Son, this is what we have found.
One by one I eliminated pieces of equipment starting with the KPA500, then the KAT100, followed
by removing the KPA100 from the K2, then changing power supplies, hooking the basic K2 to the 2.5A ps
that I power the KX3 with. This ps is about 3ft. from the K2 on the floor, under the desk. In this configuration, the audio was clean. Even though not connected, I turned the KPA500 on(which is about 4 inches from the right side of the K2) and this introduced some small artifacts which would suggest that the VCO mod would be worthwhile.

Following this, I reinstalled the KPA100. With the small PS still connected(the K2 does not recognize the KPA100), the bad audio problems returned. Disconnecting the small PS from the K2, and connecting the Astron 35m(which is about 2ft. from the left side of the K2) to the KPA100, but keeping power below 10 watts to keep the KPA100 off the results were no different. Turning the power up to turn the KPA100 on, the results were no different. Power output through an external watt meter closely follows the power selected.

What now?

73, George, NC5G



<quote author="Don Wilhelm-4">
George,

Ask yourself what has changed between good operation and now.
Have you re-arranged your shack?  The K2 is sensitive to devices with
transformers positioned within 2 feet of the left side panel - the
transformer's magnetic field modulates the K2 VFO.

As a test, move your K2 away from everything else on the desk and run a
test.

If this proves to be your problem, you can install the optional mod kit,
VCOSHLDKT.

73,
Don W3FPR


On 10/21/2012 10:48 PM, George Winship, NC5G wrote:
> After 11 years of operating and many unsolicited reports of great audio, I am
> suddenly getting not so good reports from my K2/100. Present setup is
> K2/100, KAT100, KPA500, and resonant antennas on 75 and 40 meters. Very
> rarely do SSB on any other bands. Stations seem to have trouble describing
> the problem. Reports vary from fuzziness, distortion, to clipping. I
> bypassed the tuner and amp, hooking feed line directly to K2/100 and also
> turned the power down to ten watts to shut off the KPA100 and problem
> persists. No difference between MH2 and CM500 mics. These test were done
> with stations who know my rig and my voice. This is an early K2/100. All
> mods were done years ago to K2, SSB, and KPA100. Receive audio is unchanged.
> Visual inspection of boards look OK.
>
> As a further check, I connected my KX3 to amp and antennas with great
> results.

[Don Wilhelm-4]

George,

Do you have the updated shield on that KPA100?  Shield over the speaker
magnet and a narrow notch at the SO-239 jack and solder lugs to directly
connect the SO-239 jack to the outer surface of the shield.  If you have
all those, there should be no change in the K2 behavior when installing
the KPA100.

73,
Don W3FPR

On 10/28/2012 9:25 PM, George Winship, NC5G wrote:

> After some extensive on the air testing with my Son, this is what we have
> found.
> One by one I eliminated pieces of equipment starting with the KPA500, then
> the KAT100, followed
> by removing the KPA100 from the K2, then changing power supplies, hooking
> the basic K2 to the 2.5A ps
> that I power the KX3 with. This ps is about 3ft. from the K2 on the floor,
> under the desk. In this configuration, the audio was clean. Even though not
> connected, I turned the KPA500 on(which is about 4 inches from the right
> side of the K2) and this introduced some small artifacts which would suggest
> that the VCO mod would be worthwhile.
>
> Following this, I reinstalled the KPA100. With the small PS still
> connected(the K2 does not recognize the KPA100), the bad audio problems
> returned. Disconnecting the small PS from the K2, and connecting the Astron
> 35m(which is about 2ft. from the left side of the K2) to the KPA100, but
> keeping power below 10 watts to keep the KPA100 off the results were no
> different. Turning the power up to turn the KPA100 on, the results were no
> different. Power output through an external watt meter closely follows the
> power selected.
>
>

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[George Winship, NC5G]

Don,

Yes, installed the updated shield and the KPA100 upgrade mods in 2010. A to B mods on the K2 were done in 2003. Also, did the SSB mod to broaden the bandwidth to 2.5 KHZ back then also.

73,

George, NC5G


<quote author="Don Wilhelm-4">
George,

Do you have the updated shield on that KPA100?  Shield over the speaker
magnet and a narrow notch at the SO-239 jack and solder lugs to directly
connect the SO-239 jack to the outer surface of the shield.  If you have
all those, there should be no change in the K2 behavior when installing
the KPA100.

73,
Don W3FPR

On 10/28/2012 9:25 PM, George Winship, NC5G wrote:
> After some extensive on the air testing with my Son, this is what we have
> found.
> One by one I eliminated pieces of equipment starting with the KPA500, then
> the KAT100, followed
> by removing the KPA100 from the K2, then changing power supplies, hooking
> the basic K2 to the 2.5A ps
> that I power the KX3 with. This ps is about 3ft. from the K2 on the floor,
> under the desk. In this configuration, the audio was clean. Even though not
> connected, I turned the KPA500 on(which is about 4 inches from the right
> side of the K2) and this introduced some small artifacts which would suggest
> that the VCO mod would be worthwhile.
>
> Following this, I reinstalled the KPA100. With the small PS still
> connected(the K2 does not recognize the KPA100), the bad audio problems
> returned. Disconnecting the small PS from the K2, and connecting the Astron
> 35m(which is about 2ft. from the left side of the K2) to the KPA100, but
> keeping power below 10 watts to keep the KPA100 off the results were no
> different. Turning the power up to turn the KPA100 on, the results were no
> different. Power output through an external watt meter closely follows the
> power selected.