De-Emphisis Question

[DanTana]

I have this Saba Telewatt MD-292 and it appears to have the wrong de-emphasis for the US. I'm not 100% sure about this since I don't have a schematic. So, what should I look for, and what should I change this to? There is no obvious switch from 25 to 50 or 75. I believe this is been hard wired at one setting and I'd like to make sure it's correct or fix it if needed.

Any suggestions would be appreciated.

[Punker X]

Without a scat it hard to tell where it might be. Can be anywhere from the de-mux to the last thing in the audio circuit.

X

[DanTana]

Mike, I remember reading a 1uf cap and certain resistor make up xx de-emphasis. I guess I could look it up, but should I look for a certain circuit and maybe give that a shot? I've read about this tweak before, but of course I didn't commit to memory.

[Punker X]

If your lucky its just a simple RC circuit with one cap and resistor per side. A cap and resistor form an RC circuit. To get the time constant. RC=T. If your unlucky.. there may be a resitor/cap network.. Much more advance and time consuming math involved there. Once you figure out the RC circuit, then you can figure what values have to change to get 75u sec.

X

[Aage]

Have you found a schematic for it? There may well be a note in there about use in other countries, the mods to make, etc.

[cfoster]

While we're on the subject.... This may sound stupid but, until recently, I never owned a tuner with a de-emphasis switch and have forgotten which de-emphasis setting we use here in the US. Being an old AM radio engineer, I'm afraid that most everything I ever learned about FM vanished somewhere along the way. (don't tell the FCC) Does anyone know? Thanks.

Clyde

[dewickt]

75uS

[cfoster]

75uS
Thanks!

Clyde

[Columbo]

I recently bought a Pioneer TX 9500II and took it in for service. When I got it back, the de-emphisis switch was set on 50us. It appears that it has always been set there because there are no other marks on the plastic tab that keeps the switch from accidentally being moved. From what I've read on this short thread, this is not correct.

What is this 50us used for? Why would a well known tech put the switch on this setting? I know he removed the tab to clean the switch with DeOxit.

[Punker X]

50usec is used just about everywhere except in this hemishere. (America's). Should be at 75usec. Tech must have made a mistake.

X

[renaudagnes]

75us USA, Europe = 50, Japan = 25

[Columbo]

Thanks for the responses! I've been searching AK a bit more and basically found those same answers. Not the first time this tech made a mistake on my equipment. I'll switch 'er back to 75us right now.

[ModernClassic]

USA=Japan=75us, Europe=60us, 25us is used in conjunction with a FM MPX Dolby noise reduction system ( external or built in ) and was not used for many decades.
If you find that there are too much treble and is light on bass, then there is a chance that the de-emphasis is wrong. Try to locate the de-emphasis capacitors located at the MPX circuit, add, in parallel, a capacitor ( one per channel ) of value = half of the installed value. i.e. if value is .015u, then add a .0075u in parallel with it.
Good luck.