Posted on rec.radio.shortwave

Kiwa Filters for Sony 2010 - worth it? 

From: (Crabtreejr)
Date: 18 Jun 1997 16:58:54 GMT
Newsgroups: rec.radio.shortwave

Woody  wrote on Sat, 07 Jun 1997 16:38:07 -0700

>I have been looking at the upgrade filters for the Sony 2010.
>I am hesitent to spend $64 for the (2) filters since the one
>guy who has them said they "lost audio fidelity". Since I have
>been unable to listen to a modified radio side by side, I would
>like to hear from anyone who has installed them. One other comment
>was "not many people have them, they can't be that good". I wonder
>if it is that they are not good or that Kiwa really discourages
>sending your radio to them to be worked on. It really came across on
>thier website that they try and encourage you to do your own
>installation. I have the following questions:

>1)     Do you feel that after installing the filters, the audio
        quality improved?
>2)     Did the filters reduce the hets as advertised?
>3)     Did you feel the radio perform better when adjacent signals
        were strong?
>4)     Do you feel it was worth the effort or would you reverse
        your decision to change the stock Sony filters?
>Any help would be appreciated via direct e-mail or copy postings.

I took a slightly different approach to the filter issues on the 2010.  On
6 Jan 1997, Roger Stevens wrote that he had installed the Kiwa wide filter
in the narrow slot, as he wished to get the full audio on the clear
channel stations on AM.  Prior to that Chuck Forsburg had suggested that
it would be nice to have the filters switch selectable.

I mounted a Murata CFW455HT (shown as a CFWS455HT in the 1997 Murata US
catalogue) on a separate PCB along with a duplication of some of the
Narrow filter circuitry.  I patched 6 wires onto the main PCB and put a
miniature slide switch (from Radio Shack) in the battery compartment (the
batteries still fit) to switch between the existing  narrow band filter
and the 455HT, when the Narrow Filter is selected from the front panel.
(No modifications were necessary on the main PCB, and the switch does not
directly switch any signals.)  I tend to use the 455HT most of the time.
If I need the existing narrow filter, then I remove the battery cover, and
switch to it.  As I rarely use batteries, this is straightforward.

For SW listening I tried the 455HT filter in two configurations, with the
Narrow mode audio filter operative, and disabled (more on how this was
done later).  With the audio filter disabled, there was a very occasional
trace of a 5kHz het., along with some adjacent channel interference.  With
the audio filter enabled, the 5kHz het. disappeared, and the adjacent
channel interference was much reduced.  I prefered the audio filter to be
in place for SW listening.  The clarity of the 455HT is much better than
the existing narrow filter - no muffling etc.  My experience suggests that
the poor audio quality of the existing narrow filter is caused by some
aspect of the ceramic filter, and not the 'Narrow' mode audio roll-off
circuit.

For AM there is a noticeable audio difference between the existing wide
filter, and the 455HT with the either the audio roll-off filter operating
or disabled ( I could switch between the two filters, literally at the
touch of a button, via the front panel).

If anybody wants details of my mod., then please let me know.  I will then
write it up and post it.

CERAMIC FILTERS:
I obtained my 455HT from Cirkit while I was in the UK .  The cost,
including VAT, was £2.83 ($4.55).  They carry a selection of the Murata
range of ceramic filters, including 10.7MHz filters at £0.71 ($1.15) each.
 These are necessary for the mod in Steve Whitt's book to improve the FM
selectivity.   Cirkit can be contacted by e-mail at
mailorder@cirkit.co.uk.  However, they do have a minimum order of £10,
plus a shipping charge.

The 455HT filter has come in for criticism, for having a wide tolerance in
its nominal 6kHz bandwidth.  I cannot comment as to how valid this is, but
possibly the Kiwa wide filter is a little tighter.  The Cirkit catalogue
shows that NTKK make a similar range (LFH?S series where ? represents the
nominal bandwidth ) to the Murata CFW series of filters.  Hence the
equivalent to the 455HT is the LFH6S.  I do not know if this filter has a
better shape factor than the 455HT.

Does anybody know of a US outlet which will deal in one-off quantities for
either Murata or NTKK filters?

SONY AUDIO FILTERING:
I built a model of the Sony audio circuits, using the student version of
Spice from the Internet.  I did not have specific information for Q19 or
Q20, and so I used a beta of 200.  (Variations do not make that much
difference to the audio roll-off anyway).
Ther model gives the following results, in which the 0 dB reference point
is the output at 1kHz in the 'Wide' mode.
The outputs of the model were (in dB)

                          Wide mode          Narrow mode     Narrow
(disabled)
    1 kHz                   0                -2.5            -1
    2 kHz                  -1                -3.5            -2
    3 kHz                  -2                -7              -3.5
    4 kHz                  -3.5              -11             -5
    5 kHz                  -4.5              -16             -5.5
    10 kHz                 -9.5              -32             -12
  slope / decade           -20               -60             -20

These numbers are informative.  There is an audio roll-off in Wide mode
with a -3dB at a little under 4kHz.  This is caused by the combination of
R189 and C80.  The results from the model for disabling the narrow filter
were obtained by placing a link from the junction of C81/R191 to the base
of  Q19.  The results show that the audio performance is very similar to
that of the Wide mode, but with an additional 1dB of attenuation.
I have tried this modification in practice, and believe that it is the
easiest way to disable this audio filter.  It gave a small but noticeable
improvement when using the existing narrow filter,  However with weak
noisy signals the signal quality, to me, did not improve and I preferred
to use the synchronous detector and tune away from the signal to increase
the bandwidth.  Hence I removed the link.

OTHER THOUGHTS
The fundamental problem is that two filters is not enough for all
listening modes.  There are varoius options:
i)  If you like to listen to AM and SW, then install the Kiwa wide filter
or 455HT in the narrow slot.
ii)  If your main interests are Sw and SSB/DX then install the Kiwa filter
in the wide slot and a better filter in the narrow slot.
iii)  If you want to do all three, the a switched filter arrangement is
desirable.  Kiwa now have a switched filter module, (see their web site at
www.wolfe.net/~kiwa) but I have no idea if it will fit into the 2010.  So
it appears that one has to do it oneself.

Various previous postings (see dejanews.com) on the subject of the Kiwa
filters suggest that the jury is still out on the 3.5 kHz narrow filter.
Am I correct in thinking that this is because the effective audio
bandwidth (1.75 kHz plus whatever one can get from tuning away from the
signal) is very narrow?  Has anybody tried the Kiwa 4.0 kHz filter which
they recommend for casual DX'ing?  Ideally it would be nice to hear from
somebody who has tried both, however improbable this might be.

In summary I am very happy with the addition of the 455HT filter alongside
the existing narrow one, and nothing would persuade me to remove it.  It
has also reduced my urge to replace the existing narrow filter.

jrcc

Disclaimer:  I am in no way connected with Cirkit or Kiwa.

Although we have made every effort to ensure the reliability of our
sources, we do not assume responsibility for their accuracy.
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