Several weeks ago I asked if capacitors could make that much difference

in intelibility and that such a simple question would move me to
complete,
then redesign a project from over 20 years ago.

I found that on weak and noisy signals capacitors can make a world of
difference. A little scrounging has given me a Pioneer KEHP9500 MOSFET
automitive stereo unit, with very low distortion when operated below
10W
and a set of Minmus 7 speakers. And 10W in 2 speakers is painfully
loud.

I brought the audio straight out from my R2000 and found that by
bypassing
all of the audio chain the audio was much clearer. 2nd best was to use
the
Rec out. The difference here is slight and I wouldn't swear in court
that
I am positive.

I then compared the detector direct signal with different types of
capacitors. And Craig at Kiwa is mostly correct. My only disagreement
is with the Panasonice bypolar electrolytics. I douldn't hear any
diffrence bewteen
them and "good" single ended caps. Perhaps my samples were bad. And all
electrolytics sound worse then mylar and related caps.

I then compared the best direct signal with the improved detector.
Again a hands down victory for better technology. I did a quick
comparison between
2 different improved detectors.
http://www.amwindow.org/tech/htm/lowdisdet.htm
is a simpler single IC unit, and the unit shown at
http://www.amwindow.org/tech/htm/alowdisdet.htm.
While the simple unit is much better then the stock diode, the 2nd,
more complex unit is much better then the simple unit.

I then compared the
http://www.amwindow.org/tech/htm/alowdisdet.htm unit with the AD607
synch detector. The synch detector is the clear winner.

The first comparisons showed the advantage under weak/noise conditions.

The sycnh detector is better under ALL conditions. My wife plays the
flute
and we listened to a folk music broadcast from SA and my wife said is
it was the first time a flute really sounded like a flute on the radio.

The "Vinyl Cafe'" on the CBC (13.655 10EDT) today sounded great!

Many radios would sound much better with some attention to the audio
chain.
I used to think that a "little" distortion didn't matter. After all the

signals get pretty mangled by the ionosphere. And I was wrong. It makes
a
great difference. I have spent the day listening to HF and going back
and
forth just to get a feel for it.

I experimented with better, lower V-forward, and tried biasing the
diode.
While these steps can make very minor improvements, they are hardly
worth
the minimal effort.

Most audio sections are now built from ICs. Most ICs have nasty notch
or
"cross over" distorion. If I was crazy enough to decide to rebuild the
complete audio chain I would start with a better output stage, a
discrete,
MOSFET design. I would then rework the stages to eliminate all the
electrolytics in the signal path. I would then add an AD607 synch
detector
and redesign the BFO.

My R2000s are like new receivers. I can uderstand signals that were
lost
in the noise before. For the time being I am going to live with an
outboard detector BFO combo. Kind of like the Kiwa MAP, or the Sherwood
SE-3 MK III. I
say "kind of" because I doubt that my unit approaches the quality of
either
of those units. I am still working out the details and so far have
~10KHz, 4.8KHz, 3KHz 2.1KHz and 500Hz filters with the last 2 being
crystal fitlers.
A word of advice to anyone deciding to add filters, forget the older
Collins mechanical filters. Mine at least "rings like a bell".

I am still working to intergrate the BFO, "tone tilt" filter switching
and trying to come up with a decent project case. But the effort has
been well worth the effort.

While I would love to buy a really "good" receiver like the AOR7030+,
or
one of the better Drakes, or even an NRD, money being rather tight, I
am
happy to get any improvements I can.


Terry






I finished the AD607 synhcronous detector and have
been testing it and comparing it to the stock diode
detector and to an "improved" diode detector.