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K3 SO2R audio problem

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k6rb

K3 SO2R audio problem

I have two K3s set up for SO2R using a DX Doubler. Each radio has the Top Ten cable for a K3 with a PTT, key, mic and phones plug on one end. When everything is set up and I plug my headphones into the DX Doubler's phones jack, I hear a bit of hum on the audio regardless of whether the audio switch is in Radio 1, Both, or Radio 2 position. When I send with the right radio or left radio, I hear a hummy audio. However, if I plug the headphones into either radio's phones jack, everything sounds perfect. No hum. No hummy sidetone audio. If I plug it back into the DX Doubler, and key radio 1 while the audio switch is in radio 1, and I pull the interface cable from radio 2 out of the DX Doubler socket, it all sounds fine. Same with the opposite situation, key and monitor radio 2, pull the interface for radio 1, and have headphones plugged into DX Doubler phone socket.

Looking at the DXD schematic, the audio from each radio is fed to the DXD phone socket with no active devices in the audio chain. It is strictly a switch and relay.So, physically, the two radio's audio outputs (audio 1, audio 2 and ground) are fed into the Radio 1 and Radio 2 interface sockets. The grounds on both radios are joined and the DXD's audio switch controls two DPDT relays that either serve just radio 1, both, or just radio 2 audio to the phone socket.

Clearly what I am hearing on the DXD is coming from stereo phones jack back into the DXD, or somehow getting created in the DXD. Monitoring the phones jack on the front panel I hear only clean stuff. Does anyone have any clues as to why the audio coming out of the stereo phones rear jacks should be interacting this way when being routed through the DXD?

Rob K6RB

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k6rb

problem addendum

When I pull the stereo phones plug on either radio and plug a headphone into that jack, everything sounds clean. So, whatever is going on is apparently happening inside the DXD. Very strange.

Rob K6RB

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Eric Swartz - WA6HHQ

Re: problem addendum

Administrator

This sounds like a classic ground loop problem where your DX doubler may
not be at the same AC ground potential as the K3s. Are they all
separately grounded to the same point? Same power supply too?

73, Eric

On 12/27/2010 4:48 PM, Rob wrote:

> When I pull the stereo phones plug on either radio and plug a headphone into that jack, everything sounds clean. So, whatever is going on is apparently happening inside the DXD. Very strange.
>
> Rob K6RB
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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Joe Subich, W4TV-4

Re: K3 SO2R audio problem

In reply to this post by k6rb

> Clearly what I am hearing on the DXD is coming from stereo phones
jack back into the DXD, or somehow getting created in the DXD.
Monitoring the phones jack on the front panel I hear only clean stuff.
Does anyone have any clues as to why the audio coming out of the stereo
phones rear jacks should be interacting this way when being routed
through the DXD?

This is a typical "ground loop" situation. Bond the chassis of each
K3 and the DXDoubler and power the DXDoubler from a separate power
supply (e.g., a 12V DC wall wart).

If that doesn't solve the problem you will need to insert an audio
isolation transformer in the headphone line from one of the rigs.

73,

... Joe, W4TV

On 12/27/2010 7:42 PM, Rob wrote:

> I have two K3s set up for SO2R using a DX Doubler. Each radio has the Top Ten cable for a K3 with a PTT, key, mic and phones plug on one end. When everything is set up and I plug my headphones into the DX Doubler's phones jack, I hear a bit of hum on the audio regardless of whether the audio switch is in Radio 1, Both, or Radio 2 position. When I send with the right radio or left radio, I hear a hummy audio. However, if I plug the headphones into either radio's phones jack, everything sounds perfect. No hum. No hummy sidetone audio. If I plug it back into the DX Doubler, and key radio 1 while the audio switch is in radio 1, and I pull the interface cable from radio 2 out of the DX Doubler socket, it all sounds fine. Same with the opposite situation, key and monitor radio 2, pull the interface for radio 1, and have headphones plugged into DX Doubler phone socket.
>
> Looking at the DXD schematic, the audio from each radio is fed to the DXD phone socket with no active devices in the audio chain. It is strictly a switch and relay.So, physically, the two radio's audio outputs (audio 1, audio 2 and ground) are fed into the Radio 1 and Radio 2 interface sockets. The grounds on both radios are joined and the DXD's audio switch controls two DPDT relays that either serve just radio 1, both, or just radio 2 audio to the phone socket.
>
> Clearly what I am hearing on the DXD is coming from stereo phones jack back into the DXD, or somehow getting created in the DXD. Monitoring the phones jack on the front panel I hear only clean stuff. Does anyone have any clues as to why the audio coming out of the stereo phones rear jacks should be interacting this way when being routed through the DXD?
>
>
> Rob K6RB
>
>
> ______________________________________________________________
> 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
>

Dave Hawes

Re: problem addendum

In reply to this post by Eric Swartz - WA6HHQ

Rob,

Eric is correct.

http://www.qth.com/topten/apnote9.htm

Hope this helps.

73 - Dave N3RD

On 27 Dec 2010 at 17:04, Eric Swartz - WA6HHQ, Elecraf wrote:

> This sounds like a classic ground loop problem where your DX doubler may
> not be at the same AC ground potential as the K3s. Are they all
> separately grounded to the same point? Same power supply too?
>
> 73, Eric
>
>
> On 12/27/2010 4:48 PM, Rob wrote:
> > When I pull the stereo phones plug on either radio and plug a headphone into that jack, everything sounds clean. So, whatever is going on is apparently happening inside the DXD. Very strange.
> >
> > Rob K6RB
> >
> >
> > ______________________________________________________________
> > 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
> ______________________________________________________________
> 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
>