Fm dolby output?

[sansuibutch]

My sansui tuner has a dolby fm output. I read this was a thing of the 70s but can't figure out what it does. Can somebody help me understand dolby?

 

[audiotemp]

Not an expert on this, but presumably this applies Dolby decoding, and 25 microsecond de-emphasis, rather than just 75 microsecond (or 50, I guess, in some places) de-emphasis. No point to it now, since broadcasters do not do the encoding now.

By "dolby fm output" do you mean that there is a switch, or actually a second RCA output?

 

[rcs16]

I am sure the owners manual says something about it. Dolby is/was a audio designer, he is noted for his noise reduction circuits, among others and notably better known for the tape reduction ckts. FM dolby was used to increase the signal to noise ratio in the FM system. It essentially uses signal compression in the encoder/transmitter side so that the average signal level could have greater modulation, thus lower the noise floor. It did the reverse in the receiver by using expansion circuitry to get back the same dynamic range. As said above it used a 25us pre-emphasis (higher freq) on the Tx and de-emph on the rx.
It did not catch on, as I assume that not every one bought into the idea and probably they (both broadcasters and receiver mfgs) refused to pay the royalties evolved or they did not see it as much of an improvement.
Thinking about it, if the tx was Dolby encoded/compressed and you did not have the Dolby ckts on the Rx, it would sound worse since the dynamic range is compressed. The same issue that folks claim about today, compressed music sounds lousy as it lacks dynamic range.
I am not sure if there was a automated means ( pilot signal) to determine if the rx signal was dolby encoded so the rx could automatically switch in the dolby ckts. I'd have to research it some more.

 

[sansuibutch]

Not an expert on this, but presumably this applies Dolby decoding, and 25 microsecond de-emphasis, rather than just 75 microsecond (or 50, I guess, in some places) de-emphasis. No point to it now, since broadcasters do not do the encoding now.

By "dolby fm output" do you mean that there is a switch, or actually a second RCA output?

Yes there is another set of rca outputs that say dolby fm .

 

[Punker X]

It's usually pretty easy to make these outputs 75usec and useful as a standard Fixed output. Remove the associated caps, sometimes put a shorting jumper in place depends on the tuner and how they implemented the EQ.