I do not claim ownership of the information which follows. I have had this information since the early 90's. I can't remember where I got it (possibly off packet radio) or who was the original author.

I have made the modifications described below to my 2010 and, at an ODXA DX Camp, to a few other 2010's. The improvement is definitely noticeable.

                  Some Audio Section Mods
                   for the Sony ICF-2010


This paper describes some very simple modifications to the
audio section of the Sony ICF-2010 (2001D).

VERY IMPORTANT

1)   Disclaimer notice: Do all of this at your own risk.
     Soldering iron burns, electrical shocks, frying the
     receiver, or any other surprises are your problem, not
     mine.  These mods will obviously blow the warranty.

2)   Make sure you really know what you're doing and can
     deal with surface-mount components and dense PC board
     soldering.  Follow all of the normal anti-static
     practices.

3)   This work can only be done with the full Sony service
     manual in hand.  It diagrams the circuits being
     modified and is necessary for physically locating
     certain components on the PC board.


THE PROBLEMS

In the WIDE filter mode, the 2010 passes more high frequency
audio than is useful.  This mode is really only practical
for very clear channel listening.

At the same time the NARROW filter mode is really too
muffled to be useful.  It is somewhat better if the receiver
is tuned off-carrier by about 1 khz, but that is beyond the
tracking range of the sync detector.


THE CIRCUIT

Q19 and related components form a simple low pass filter
labeled "AF LPF" in the diagram.  In the NARROW mode, Q19 is
biased on and becomes an emitter follower.  In WIDE mode,
Q19 is biased off.

Q20 is simple emitter follower like Q19, but is not a low
pass filter.  It is turned on in the WIDE mode and off in
the NARROW mode.


THE SOLUTION

The fundamental ideas are:

-    Use the LPF in the WIDE mode, cutting out some of the
     excessive high frequencies.

-    Eliminate the LPF in the NARROW mode, reducing the
     muffled audio.

-    Also in the NARROW mode, reduce some of the low
     frequencies to reduce the boominess.

This is all very easy.  Q19 and Q20 are switched on and off
through 10K resistors R194 and R197 from signals at IC13.
We're simply going to swap ends of these resistors.  The
original parts are surface-mount and are replaced with
normal components with leads.

Remove and discard R197 and R194.  Replace them with 1/4 or
1/8 watt 10k resistors, but swap the switching signals.  Now
the LPF is used in the WIDE mode and not the NARROW mode.

To reduce the bass response in the NARROW mode, remove and
discard C171 (0.01uf).  Replace it with a small 0.001uf
capacitor.  C171 couples the signal into Q20, and by
reducing it, forms a simple high-pass filter.  Other values
were tried, but this seems to be the best overall
compromise.


TONE CONTROL

One additional modification is useful.  The three-position
tone control could use more high-frequency cut in the "NEWS"
position.  Connect a 0.1uf cap in parallel with the existing
C93 (0.068uf).


RESULTS

These changes made the 2010 MUCH more useful to me.  I used
the following as a very subjective metric:  In school I
studied Spanish, but am now very rusty.  Occasionally I tune
into some Spanish broadcast and try to follow the announcer.
Previously in the NARROW mode I couldn't even pickup enough
of the sound of a word to look it up in a dictionary.  Now I
never have that problem.  Because I can pick out syllables
much more easily, I recognize many more words.  English
also, is easier.

The new WIDE position response reduces adjacent station
interference somewhat and is much more useful for shortwave
listening.  Previously it was really only good for the AM
broadcast band.


DESIGN TRADEOFFS

The only useful thing the LPF did for the NARROW position
was to reduce some high-frequency noise.  With these
modifications, the noise is more noticeable with very weak
signals.  But the more effective tone control "NEWS"
position reduces the noise, but without the original muffled
sound.

Since the WIDE mode now has a LPF in it, "hi-fi" AM
listening is less hi-fi.   FM sound is unaffected.