[Elecraft] Audio Improvements on a K2

[Ron D' Eau Claire]

Robert, VE3RPF wrote:

> I really like my K2 but would like to improve on the SSB audio.  My K2 is
> unmodified and I would like to hear from the list which  improvements you
> have made to make the K2 sound better in SSB reception.  I have done the
> spectrogram and my K2 has all the options except the RS232 option.  I know
> there are several mods out there for this rig but I only want to
> do the ones
> that are essential to improve audio.

For good RECEIVE audio, the "2nd Filter Flattening Mod" shown under
Builder's Resources is ESSENTIAL and recommended by Elecraft. According to
Wayne, it is due to become a part of the basic K2 when they next revise the
r-f board.

Without this mod, a tilt in the bandpass of the 2nd i-f filter (this is the
"cleanup filter at the output of the i-f amp) emphasizes the low frequencies
on one sideband, making it sound bassy or 'muddy', and emphasizes the high
frequencies on the other sideband, making it sound 'tinny'.

The mod greatly flattens the 'tilt' in the bandpass, providing consistent
good quality on both sidebands.

Note that this mod affects RECEIVED audio only.


>
> My second question is that i am using a radioshack mike and am told my
> transmit audio is too much on the high side.  What mike seems to work well
> with the K2 and give a nice signal?


Although I do not do a LOT of SSB work, I have gotten a number of  excellent
audio reports with my Radio Shack 21-1172D microphone.

I have also heard K2's with GHASTLY audio quality, including some using the
Elecraft Heil Microphone.

I suspect that your problem, like theirs, is in the transmit filter
alignment.

First of all, be SURE you have the OPT1 filters set up as instructed by
Elecraft. If you are going to deviate from their instructions at all for the
OPT1 filters (e.g. use Spectrogram, etc.), be sure that you check your own
audio quality after you tinker with them. The OPT1 filters are the ones used
for transmitting, regardless of which filter you have selected for receive.
If you want to change the filter setup for receive to better suit your
preference in listening, change one of the filters other than OPT1 and leave
OPT1 as specified by Elecraft.

As you will see in the SSB module setup instructions, Elecraft suggests that
TINY changes in the BFO frequency might be made in the OPT1 filter to get
the best quality. But these should only be done if you can check your audio
quality after you have done it.

I checked my audio quality by hooking my K2 to a dummy load, and then tuning
in my signal on a second receiver. If you listen to yourself talk while
listening to the second receiver in your headphones, you can tell when you
have the auxiliary receiver exactly on frequency. Then hook up a tape
recorder and RECORD some of your audio on the auxiliary receiver and play it
back to assess its quality.

It is not possible to hear what your audio really sounds like when talking
and listening in the phones. Audio, particularly the bass range, conducts
through the bones of your head and it's impossible to separate that sound
from what you are hearing in the phones. The sound of your audio will be
very different when you stop talking and play back the tape. In general, the
low frequencies will be a lot weaker. Of course, if you have a helper, you
have him/her talk into the mic while you listen on the phones.

Ron AC7AC
K2 # 1289