[Elecraft] Help with distorted [K3] transmit audio

[Mike Scott]

Today using SSB on 40M my K3 came up with pinched audio, the other operator
asked me to take the "clothes pin" off my nose. Full (and good) audio was
obtained with a power cycle. I was told that signal strength came up
significantly after the power cycle.

I have posted this issue four times now. The problem doesn't surface
everyday. I had thought my problem had something to do with HRD or use of
the Elecraft K3 utility as in the past these had been used before the
condition arose. But today I started the rig in the morning after a longish
shutdown while I attended Pacificon. I did not use HRD or the download
facility this morning so I no longer think that using those programs is
involved with my this problem. 

The audio sounded like all highs in the monitor headset. The usual suspects
have been looked at like the Tx equalizer and filter set up, that's what
everyone has said to look at every time in the past. One and only one action
is performed to bring the audio back to full and that is cycling power. I
believe this fact rules out most set up issues.

I suspect a firmware bug but it seems strange that I am the only target.
Pinched audio could mean that the SSB signal isn't centered properly in the
pass band of the 2.7 KHz Xtal filter, the rig is trying to transmit through
the 500 Hz filter or the DSP is improperly initialized. Is there a relay
contact that could be intermittent that could cause these symptoms, like one
that switches in the 2.7 KHz filter?

I have seen the same audio distortion using front and back microphone
connectors and with two different microphones, one electret with bias the
other dynamic without bias. Both microphone setups will get good audio
reports after a power cycle. 

I run 13.8V from a 35 amp linear Astron power supply. Voltage drops to 13.1V
with 100W key down so I don't think there is a marginal power supply
condition. I have 13 KHz, 6 KHz, 2.7 KHz, and 500 Hz filters. SSB is only
enabled on the 2.7 KHz filter. 

Mike Scott - AE6WA
Tarzana, CA (DM04 / near LA)
K3-100 #508/ KX1  #1311