[Elecraft] K3 Audio our artifacts

[Dave Hachadorian]

I would guess that the headphone output is expecting a low Z
(~16 ohm?) termination, and your sound card has a high Z in.
Try a terminating resistor across the headphone jack in
parallel with your sound card.

Just a guess.

Dave Hachadorian, K6LL
Yuma, AZ

----- Original Message ----- 
From: "Mike Scott" <mike at paxsen.com>
To: <Elecraft at mailman.qth.net>
Sent: Monday, March 02, 2009 5:36 PM
Subject: [Elecraft] K3 Audio out artifacts


>I have been investigating audio artifacts in connection
>with the K3 AGC hold
> experimental firmware. As a reminder, I live in a high
> noise area.
>
> As part of the investigation I have been looking at both
> Line Out and
> headphone audio using Spectrumlab on my PC.
>
> I am finding substantial 60-hz contamination on headphone
> audio that I do
> not see on Line Out.
>
> On Line Out I see what looks like fairly clean audio with
> donor lines at
> 2400 Hz and 3600 Hz outside the rx filter pass band (1 KHz
> DSP filtering). I
> presume these are the 40th and 60th harmonics of 60 Hz.
> They are 50 dB below
> noise background noise.
>
> With only a change of where I plug the PC audio cable
> (moving from Line Out
> jack to rear headphone jack) the audio looks quite
> different.
>
> Now I see a whole array of 60 Hz artifacts. The 3rd and
> 5th harmonics are
> about equal to comfortable listening level audio.  As I
> look higher in
> frequency the harmonics generally reduce in level but only
> to about 20 dB
> below comfortable audio listening level. There is also a
> broad artifact (300
> Hz wide) at roughly 3300 Hz that is also 25 dB down.
>
> The artifacts do not go away with reduced volume control
> settings but remain
> a constant feature of headphone audio out at any setting.
>
> Is there something about my test set up that I do not
> understand?
> Does anybody else see contamination of headphone audio on
> their K3?
> Could there be something wrong with my K3?
> Could transformer coupling (Line Out) vs direct coupling
> (headphone) be
> adding something to my test set up that I am not factoring
> into the problem?
>
>
> I have never quite believed the audio of my K3 was like
> Wayne says it should
> be but can make it better using slow AGC (separate post),
> I doubt that has
> anything to do with the artifacts I see here.
>
>
> Mike Scott - AE6WA
> Tarzana, CA (DM04 / near LA)
> NAQCC 3535
> K3-100 #508 / KX1  #1311
>
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