[Elecraft] Muddy SSB

[Ron D'Eau Claire]

I hate it when I discover something wrong with something I don't use often.
The compulsion to "fix it" is as strong as if I needed it every minute.

So it is with the audio quality on SSB on my K2. As others have mentioned,
the Upper Sideband, in transmit, sounds "muddy", "constricted"... lots of
terms have been used. They all add up to "awful audio" compared to the Lower
Sideband.

Until I started working on this problem, it had been nearly a decade since
my last SSB QSO. That is until one night I got on to chat with Lou, W7DZN
specifically to try out the K2 in SSB. I thought I had the BFO settings
tweaked. Not so. We spent an hour doing "on the fly" changes to my BFO
settings for the best audio quality. The USB never did get quite "right".

We ASSUMED (watch out for that word, it bites) that the problem was the
point of the low frequency cut off setting on the filter. That is, fixing
the problem was a matter of getting the BFO on the right frequency relative
to the filter bandpass. My BFO settings were very close to the Elecraft
recommendations and the spectrogram images looked just like the examples
posted in several places.

Today I made a few recordings of my own voice.  I recorded my own voice on a
good tape recorder with the K2 in SSBA-BAL mode with the recorder plugged
into the K2 headphone jack. So the "tuning" of the received audio should be
perfect. As Lou reported, LSB is fine. USB sounds like I'm in the bottom of
a barrel with a pillow over my face.

Moving the BFO frequency does not make a substantial difference. Indeed, the
problem does NOT appear to be with the low frequency cutoff, but with a loss
of most of the high frequencies on USB!

This is NOT apparent on receive even when using the OPT1 filter for receive.
Both sidebands of signals sound very good on receive (I have installed the
filter flattening mod). Spectrogram does not show any significant difference
in the shape of the bandpass between the two filters out past 2.5 kHz. Yet,
most of the higher audio frequencies (above probably 800 Hz) are highly
attenuated on only the USB.

In short, there is NO evidence of anything in the OPT1 filter that is
causing this, and I can't imagine what else in the K2 could cause loss of
high frequency response on one sideband but not the other!

Any ideas out there??

I'm apparently not the only one experiencing this. I've heard
similar-sounding K2's on the air and there have been other posts on here
about a problem that sounds just like this.

Ron AC7AC
K2 # 1289