[Elecraft] K3s+KPA500 SSB Audio Distortion

[William C. Johnson]

Michael I also have the same problem. Worked on it with Elecraft Support several times to no avail. 
I have tried several different microphones, antennas, baluns. Still no joy. I also use 18 watts drive, I had not thought of anything other than rf feedback. I will play with different drive levels.In frustration I have quit using the KPA-500. I hope you are on to something.
Bill J K7BRR Yuma

Message: 2Date: Wed, 01 Aug 2018 10:19:04 -0400
From: Michael Blake <k9jri at mac.com>
To: Elecraft Mailing List <elecraft at mailman.qth.net>
Subject: [Elecraft] K3s+KPA500 SSB audio distortion
Message-ID: <312A3CD1-8C02-4B75-B39D-D93ECAF477CB at mac.com>
Content-Type: text/plain;    charset=utf-8

While on the air on 3710 SSB I receive audio reports that say my transmitted audio is somewhat muffled or nasal.  Making adjustments to mic gain, compression levels, TX EQ seems to make no difference to this report. These adjustments do change the sound of the audio but do not reduce the reports of muffled or nasal characteristics.

I normally run the KPA500 at 500 watts PEP output and the K3s is set to 18 watts to achieve this output.

This morning I suspected that this nasal sound might be related to running the K3s at 18 watts as that uses both the 100 watt amplifier and the 12 watt amplifier but in series at very low drive levels.  As a test I cut off the KPA500 and ran the K3s at 100 watts and the distortion was gone.  As a second test I dropped the drive to 11.9 watts which dropped off the 100 watt amplifier module and runs the low power module at almost full power and the audio was still clean with the KPA500 delivering about 300 watts PEP.

Is this something that anyone else has observed?  Are there any built in tests or adjustments that might help this issue?  I have run the transmitter gain calibration at all three power levels with satisfactory results.

Oh yes,?.  The condition is the same using a dynamic mic (EV RE50), an Electret Mic (MH4 & CM500) or mic audio from a USB connected computer (Blue Yeti).

Very 73 - Mike - K9JRI