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how would i use this?

68.108.173.65

Posted on January 19, 2024 at 10:28:42

ltman

would it reduce the hiss in stereo reception that my scott 112b produces? even with the yagi antenna, I get annoying stereo hiss listening to my preferred station from the scott that is not present with my st-j75, f90, or even my dynaco fm-3.

How would I connect it to my scott?

http://www.fmmpx.com/html/the_design_.html

external mpx

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RE: how would i use this?

ltman

17:13:34 01/27/24

RE: how would i use this?

openmind

10:15:46 01/30/24

RE: how would i use this?

ltman

19:58:26 02/03/24

...

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RE: how would i use this?

ltman

17:13:34 01/27/24

RE: how would i use this?

openmind

10:15:46 01/30/24

RE: how would i use this?

ltman

19:58:26 02/03/24

well it works I guess

ltman

21:37:52 02/05/24

RE: how would i use this?

ltman

11:59:10 01/27/24

IF the LT-112B has a detector output, you can use an external MPX unit

mhardy6647

16:44:55 01/20/24

RE: how would i use this?

6bq5

12:29:21 01/20/24

RE: how would i use this?

ltman

11:59:24 01/21/24

RE: how would i use this?

6bq5

12:42:36 01/21/24

RE: how would i use this?

ltman

21:53:40 01/21/24

RE: how would i use this?

openmind

09:13:08 01/22/24

RE: how would i use this?

openmind

14:09:32 01/22/24

RE: how would i use this?

openmind

20:08:33 01/22/24

RE: how would i use this?

openmind

20:12:40 01/22/24

and it seems there are plenty of LM4500s available on the bay

ltman

12:15:04 01/27/24

RE: how would i use this?, posted on January 20, 2024 at 12:29:21

6bq5
Audiophile

Posts: 4592
Location: SF Bay
Joined: August 16, 2001

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

IF the LT-112B has a detector output, you can use an external MPX unit, posted on January 20, 2024 at 16:44:55

mhardy6647
Audiophile

Posts: 16188
Location: New England
Joined: October 12, 1999
Contributor
Since: October 23, 2016

If not... I'd say it's more trouble than it's worth to try to hack one in.

Given that the LT-112B was a kit, it might be possible, but non-trivial to do it 'right', I'd expect.

As 6BQ5 noted, the alignment of your specific tuner may be a factor.
The quality of the signal going in is also paramount, especially in stereo. How far away is the station and what kind of reception (i.e., signal strength) are you getting? Any multipath issues? E.g., a building or hill between you and the transmitter, or is the signal able to get to you directly as well as via a "bounce" from same? What are you using for antenna? How high is it? Unless truly omnidirectional -- how is it aligned with respect to the transmitted signal's origin?

Hiss does kind of come along for the ride with MPX stereo.

Also, not sure how well that Scott tuner deals with modern "HD" (hybrid digital) broadcast signals.
all the best,
mrh

RE: how would i use this?, posted on January 21, 2024 at 11:59:24

ltman

[[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?, posted on January 21, 2024 at 12:42:36
6bq5 Audiophile Posts: 4592 Location: SF Bay Joined: August 16, 2001	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?, posted on January 21, 2024 at 21:53:40
ltman	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?, posted on January 22, 2024 at 09:13:08

openmind
Audiophile

Posts: 184
Location: Phoenix
Joined: November 8, 2008

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

RE: how would i use this?, posted on January 22, 2024 at 14:09:32

openmind
Audiophile

Posts: 184
Location: Phoenix
Joined: November 8, 2008

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

RE: how would i use this?, posted on January 22, 2024 at 20:08:33
openmind Audiophile Posts: 184 Location: Phoenix Joined: November 8, 2008	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?, posted on January 22, 2024 at 20:12:40
openmind Audiophile Posts: 184 Location: Phoenix Joined: November 8, 2008	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.

RE: how would i use this?, posted on January 27, 2024 at 11:59:10
ltman	very cool work! I thought however that KCNV in Vegas does not broadcast HD radio on the same frequncy. If that is the case, could the hiss still be caused by HD signal?

and it seems there are plenty of LM4500s available on the bay, posted on January 27, 2024 at 12:15:04
ltman	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...

RE: how would i use this?, posted on January 27, 2024 at 17:13:34
ltman	I will try this also. Should be a fun experiment: LM1894 Dynamic Noise Reduction System DNR

RE: how would i use this?, posted on January 30, 2024 at 10:15:46

openmind
Audiophile

Posts: 184
Location: Phoenix
Joined: November 8, 2008

HDRadio.com shows two streams from that station :-(.
89.7 right?

https://hdradio.com/stations/

RE: how would i use this?, posted on February 3, 2024 at 19:58:26

ltman

yep, I guess you are correct. 89.7, KCNV. So it could be HD hiss, although none of my other 3 vintage tuners have any hiss at all, although the FM-3 had about the same amount of hiss until I fixed it with the "rca jack grounding upgrade" and a replacement rectifier tube.

For fun I am trying this thing. I will put two 9 volt batteries in series to get 18 volts.

It will be interesting experiment. And cheap enough.

If this DNR does not work out, I will try aligning the tuner.

well it works I guess, posted on February 5, 2024 at 21:37:52

ltman

Not sure of the overall sound quality yet. I was testing with an almost dead 20 year old walkman type player in case there was a flaw in the board or my wiring.

It definitely changes the sound as I adjust the pots. Sounds very compressed and lack of dynamics and bass when pots are at max, and not much change if any to the sound when pots are at minimum.

So next I will try with a quality source and see how it sounds. I will need to pull my Scott 112B out of storage to check the hiss reduction and sound quality.

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