K3: Rough audio with amp even using voice recorder

[Ignacy]

Someone played recording of my audio and it sounded a bit harsh. This is K3 serial number 22xx with Expert 2k-fa. Same harshness with either the microphone or the voice recorder. No harshness without the amp.

Similar harshness with power limited to 500W. I suspected the amp's nonlinearity. But KX3 with the same amp (400W out) sounds smooth.

So it seems to be a feedback but not via a microphone.  Any idea of what is going on?

Ignacy, NO9E

[Jim Brown-10]

On Tue,9/16/2014 7:55 AM, Ignacy wrote:
> Similar harshness with power limited to 500W. I suspected the amp's
> nonlinearity. But KX3 with the same amp (400W out) sounds smooth.

I would suspect that the amp is being overdriven. How much power out
from the K3? Are you using ALC between the K3 and the amp to set the TX
power? That's a known cause of nasty distortion. The right way to do it
is to reduce power from the K3 until you get the desired output from the
amp.

73, Jim K9YC

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[Ignacy]

I reduce the power to one half, and no change. Also the problem varies from band to band.

Ignacy  

On Tue, Sep 16, 2014 at 11:28 AM, Jim Brown-10 [via Elecraft] <[hidden email]> wrote:

On Tue,9/16/2014 7:55 AM, Ignacy wrote:
> Similar harshness with power limited to 500W. I suspected the amp's
> nonlinearity. But KX3 with the same amp (400W out) sounds smooth.

I would suspect that the amp is being overdriven. How much power out
from the K3? Are you using ALC between the K3 and the amp to set the TX
power? That's a known cause of nasty distortion. The right way to do it
is to reduce power from the K3 until you get the desired output from the
amp.

73, Jim K9YC

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[Don Wilhelm-4]

I would first suspect RF feedback.
What happens if you use only the K3?  Connect the K3 to a dummy load and
listen with your KX3.  That will tell you more than having someone do a
recording off the air.
If the K3 is clean, then you can conclude it is either the amplifier or
RF Feedback.
If the bare K3 still has a problem into a dummy load, look at the TX EQ
settings.

73,
Don W3FPR

On 9/16/2014 12:10 PM, Ignacy wrote:

> I reduce the power to one half, and no change. Also the problem varies from
> band to band.
>
> Ignacy
>
> On Tue, Sep 16, 2014 at 11:28 AM, Jim Brown-10 [via Elecraft] <
> [hidden email]> wrote:
>
>> On Tue,9/16/2014 7:55 AM, Ignacy wrote:
>>> Similar harshness with power limited to 500W. I suspected the amp's
>>> nonlinearity. But KX3 with the same amp (400W out) sounds smooth.
>>

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[Jim Brown-10]

On Tue,9/16/2014 9:10 AM, Ignacy wrote:
> I reduce the power to one half, and no change. Also the problem varies from
> band to band.

HOW do you reduce the power? Do you turn down the K3, or do you turn
down the amp?

73, Jim K9YC
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[Ignacy]

I reduce power in K3. Note that the problem occurs with the voice recorder. 

Ignacy

On Tue, Sep 16, 2014 at 2:27 PM, Jim Brown-10 [via Elecraft] <[hidden email]> wrote:

On Tue,9/16/2014 9:10 AM, Ignacy wrote:
> I reduce the power to one half, and no change. Also the problem varies from
> band to band.

HOW do you reduce the power? Do you turn down the K3, or do you turn
down the amp?

73, Jim K9YC
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[Jim Brown-10]

On Tue,9/16/2014 1:16 PM, Ignacy wrote:
> I reduce power in K3. Note that the problem occurs with the voice recorder.

Good. I agree with Don -- RF feedback or excessive TXEQ are
possibilities. How is your TXEQ set? Is anything boosted? Are the bottom
three bands turned way down? What mic, how is it wired, how/where do you
plug it in? Were you transmitting with the amp when you recorded the
messages for the voice recorder?

I also agree that you should try to listen with the KX3 with its antenna
disconnected.

73, Jim K9YC
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[Ignacy]

I did extensive testing with amp on/off, eq on/off, a different microphone, as suggested. Differences are not dramatic. 

What seems to be going is that the voice becomes distorted past 12W at K3. Linear at 12W and scratchy at >12W. A bit better at 100W.

I looked at currents with no signal.  1.1A in RX. 1.9A at 12W. 2.0A at >12W. High power turns on HPA, and it seems that the idle current for HPA should be > 0.1 A.  At whistle: 3.5A at 12W and 20A at 100W.

Ignacy 

On Tue, Sep 16, 2014 at 8:49 PM, Jim Brown-10 [via Elecraft] <[hidden email]> wrote:

On Tue,9/16/2014 1:16 PM, Ignacy wrote:
> I reduce power in K3. Note that the problem occurs with the voice recorder.

Good. I agree with Don -- RF feedback or excessive TXEQ are
possibilities. How is your TXEQ set? Is anything boosted? Are the bottom
three bands turned way down? What mic, how is it wired, how/where do you
plug it in? Were you transmitting with the amp when you recorded the
messages for the voice recorder?

I also agree that you should try to listen with the KX3 with its antenna
disconnected.

73, Jim K9YC
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