Mike Bugaj
I swore that I was not going to mod any other FM tuners. I wasn't, until I
found this one.
The first TU-920 I bought was purchased at a local flea market for
almost nothing. After I brought it home and turned it on, I found that
it had some nice features to it. I found that the tuner does have
wide/narrow IF and that it does have four ceramic IF filters;
two 230khz and two 180khz filters. This tuner, in stock condition, has
about the same selectivity as an unmodified Carver TX-11 tuner
(which has five filters, two of them 180khz filters.) But the
Harmon-Kardon tuner sounds much better! Unfortunately for me, I blew out
the tuner while trying to find a tapping point on the main board for RDS.
So, I looked at eBay for another one, and some weeks later I bought
another TU-920, but for a little bit more than I paid for the first
one, but still it was not expensive. And after having used it for some
months, I finally decided to modify it with two 110khz
filters, and I did.
First, here's what the board looks like:
Changing two silly filters seems easy enough. What makes it a bit more complicated
is that the transformer wires must be unsoldered and the display
unplugged as well as all other connectors on the board. The board must
be physically removed from the tuner. Once that's done, removing and
replacing the filters is fairly easy. The blue filters are the originals.
The other two are the 110khz replacements. The tuner does
not have a wide/narrow IF switch on the front panel. It does have an
"active tracking" switch on the panel instead, and turning on active
tracking switches the tuner into narrow IF mode. Supposedly the
selectivity is automatically adjusted for strong and weak stations as
you tune. It works good.
Rather than try again to find a point to tap into for RDS, I tried to make my Conrad
RDS Manager work by splicing into one channel of the audio output.
Since this method hardly ever works, I had no expectations, but the RDS
Manager will work perfectly fine when split into one side of the audio
output line if the tuner is switched into monaural mode and not stereo.
Too bad I hadn't tried this first on my original TU-920. If you have an
RDS manager laying around, this is a tuner you can use it with. Just
buy yourself a "Y" adapter and you're good to go. You get sensitive RDS
without taking the cover off the tuner. It can't get easier.
The tuner has 16 presets. There are two banks of eight each.
Have you noticed that this tuner has a tuning dial? DXers love tuning dials.
However, don't be fooled like I was. The dial is nothing more than a
rocker switch. Turn clockwise and it stops and you go up 100khz. Turn
CCW and you go down 100khz. Turn it to either extreme and hold it and
it will keep tuning up or down the dial until you release it. I put up
with this "dial" but up/down buttons would have been better than this.
I compared the resulting selectivity to the selectivity of my Sony XDR-F1HD tuner and
the H-K is very close. The Sony's don't cost very much these days but
if you can find, buy (or win) one of these tuners for $50 or less,
you'll have made a good deal especially if you don't find a little
soldering with a filter change.
©2008-2012 M. Bugaj