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RE: how would i use this?

52.119.121.37

6bq5

In Reply to: RE: how would i use this? posted by ltman on January 19, 2024 at 10:28:42

The Scott LT-112B is an interesting beast from a quick search.

Given that it is a late(well after the introduction of MPX and the selection of the subcarrier channel) tuner (also mostly SS), has an MPX circuit built in.
Adding a second external MPX filter may not help it at all-

There are some old comments here in the 'Radio Road' forum that indicate it is not one of their best efforts

Tuner Info has a better review of the unit - but the reviewer was able to align the unit himself and was quite happy with the results.

As with all tuners, what is the antenna?
That is where the next amount of focus should be placed-
Good antenna can make an incredible difference
even an OK antenna well placed is better than not paying attention to the antenna...
Happy Listening

Follow Ups:

RE: how would i use this? - ltman 11:59:24 01/21/24 (7)
[[As with all tuners, what is the antenna?]]
4 element yagi coax to balun at the tuner, with line of sight from 2nd floor porch to tower 26 miles away. But KCNV has relatively low wattage.

The thing is that my sony st-j75, pioneer f90, and even the Dynaco FM-3 have virtually no hiss with that antenna and station. That is what has me confused.

Maybe the Scott just has lower sensitivity for stereo decoder. No hiss at all when switched to mono. And it is a musical sounding tuner, but the hiss is too annoying in stereo for me.
- RE: how would i use this? - 6bq5 12:42:36 01/21/24 (6)
  Remember the Scott unit was a kit.
  It might be fabulous, after an alignment...
  
  Your antenna sounds wonderful, and if the Scott was running well, you could enjoy it-
  
  I do Like the Scott tuners- but mostly the tube units along with the 4310...
  
  Happy Listening
  - RE: how would i use this? - ltman 21:53:40 01/21/24 (5)
    I believe the 112b alignment procedure documented in the assembly manual is intended to be performed without external test instruments, by using the tuner's meters, so that will be something to try.
    - RE: how would i use this? - openmind 09:13:08 01/22/24 (4)
      The symptoms you describe sound a lot like IBOC noise. The best documentation on that is on Brian Beezley's page below.
      
      http://ham-radio.com/k6sti/hdrsn.htm
      
      The good news is that your Scott has oscilloscope outputs. One of those is the FM detector output. That can drive the external decoder.
      
      I've used that decoder and I suspect it will reduce or eliminate your problem. You can also add a post-detection filter before the decoder.
      
      The bad news is that the LM 4500 chip is out of production. I don't know whether Mr. Fitzgerald is still offering the chips and boards. It would be best to contact him directly through that site. Good luck!
      https://www.usaudiomart.com/details/649544801-hh-scott-lt-11 (Open in New Window)
      - RE: how would i use this? - openmind 14:09:32 01/22/24 (3)
        
        In Reply to: RE: how would i use this? posted by openmind on January 22, 2024 at 09:13:08
        
        To oversimplify, your tuner has a front half which receives the broadcast and sends a composite signal to a multiplex decoder. The back half of your tuner is the multiplex (stereo) decoder, which decodes it into left and right audio, which is then fed to your system.
        
        The horizontal output on your Scott carries the composite signal. That would be fed to your added decoder. That decoder has two audio outputs, which are fed to your system instead of the left and right audio outputs of your tuner.
        
        You are substituting the external decoder for the back half of your tuner.
        
        The design of the decoder has a huge impact on the amount of IBOC noise from HD radio.
        http://ham-radio.com/k6sti/mpath.htm (Open in New Window)
        
        RE: how would i use this? - openmind 20:08:33 01/22/24 (2)
        
        In Reply to: RE: how would i use this? posted by openmind on January 22, 2024 at 14:09:32
        
        This photo shows a little box I had made with one of those inside. You can see the left and right audio outputs, which I connected to my preamp.
        
        Below that is the input jack for the DC power supply.
        
        The cord coming out went to the MPX out of my Citation III-X tuner. It was used in place of the MPX decoder that was built into the Citation. I think that is what you want to do with your Scott.
        
        RE: how would i use this? - openmind 20:12:40 01/22/24 (1)
        
        In Reply to: RE: how would i use this? posted by openmind on January 22, 2024 at 20:08:33
        
        This photo shows one of these decoders mounted inside a Sherwood 3000 tuner. The Sherwood had space and wiring for an optional Sherwood decoder. I used one of the fm-mpx boards in its place. The DC for the board came from the tuner's heater supply.
        
        and it seems there are plenty of LM4500s available on the bay - ltman 12:15:04 01/27/24 (0)
        
        In Reply to: RE: how would i use this? posted by openmind on January 22, 2024 at 20:12:40
        
        Don't know if they would be authentic, although I would presume so since it doesn't seem it would be profitable even for the chinese to knock off that chip...

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