Is there anything more
fun than listening to E Skip? Or staying up all night logging long haul
tropo, or going to bed at 4am and getting up for work at 8?
HARMON-KARDON TU-911 FM TUNER (9/08)
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