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List:       elecraft
Subject:    Re: [Elecraft] KX3 headphone output impedance and recommended speaker
From:       Don Wilhelm <donwilh () embarqmail ! com>
Date:       2019-06-29 17:44:11
Message-ID: 4a1c4c10-e290-81e1-bb8b-6faa83b795d8 () embarqmail ! com
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Dennis,

Impedance matching in audio circuits has not been important since the 
days of vacuum tubes with audio output transformers.

Were you operating the KX3 on batteries when you found that oscillation? 
  If so, the internal resistance of the batteries would be the cause of 
the oscillation.

For the computer connection, just use standard stereo audio cables - no 
need to match impedance - just set the audio level correctly.

For amplified speakers, I recommend West Mountain Radio COMspkr mainly 
because they are shielded and do not howl with the transmit RF.

73,
Don W3FPR

On 6/29/2019 1:01 PM, Dennis via Elecraft wrote:
> I searched the KX3 manual and could not find a specification for the \
> headset/speaker output jack. Last weekend at Field Day I plugged in a low impedance \
> speaker and got some oscillations above a certain output level. 
> I want to optimize the impedance match to my computer for FT8 and also know what \
> speaker impedance would be the best match for my KX3. 
> Also, what would be the preferred after-market amplified speaker for the KX3?
> 
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