RBJs Tuner Treatise

[redbenjoe]

have observed from years of empirical evidence--
that spec FM stereo reception for any size//type DC powered box
( from walkman thru biggie grail)
depends on top spec battery voltage...

ie if the set of batteries is putting out any less than the rated voltage-
the tuner performance drops off dramatically ( like to shitte)

surely tuners dont require a big amp draw -
but they really NEED full voltage... right ?

with a set of semi-weak batteries -
i can play my boomers LOUD- and with ALL the bass -
and the decks work to speed and fine
and the AM radio is very strong

its only the FM that dies FAST !!!
--------------------------------
can any of you tech guys confirm - via science that this is always the case ??

 

[Superduper]

It's true. Battery voltage is not as critical with amp and motor functions. They have a voltage range that they can work with.

However, tuner circuits are, shall we say, "tuned" and as such, rely on a stable voltage supply. It is no wonder then that they usually incorporate a separate voltage regulator that is below the normal system voltage. You may find that your tuner is zener regulated at 8 volts on a 12volt boombox. So as long as your system voltage is above the regulated voltage, the tuner will perceive full power. But once the main voltage drops below the regulated voltage, then the regulator will only pass the lowered voltage on, and performance suffers.

That's quite perceptive, for an old fogey.

 

[skippy1969]

Very interesting.......

 

[redbenjoe]

THANKS

unfortunately --the stuff i have might not have that nifty
'lower voltage floor -
as it takes not much voltage drop to weaken the tuner

 

[Ken]

So you're saying, Norm, that on a graph of voltage vs time, the knee of the curve is the minimum operating voltage for said tuner? This I guess kinda means that your tuner function would deteriorate as fast as that curve drops past the knee. My experience is that the curve is pretty steep after that for most batteries.

 

[baddboybill]

Yes I've noticed that when battery power gets low you lose stereo from the tuner but you still hear it in mono

 

[Lasonic TRC-920]

Very interesting.......

 

[Eddy]

I worked on a GF 9595 before . In this box is a voltage converter that converts 5 V DC into 15 V . The PLL tuner in that thing needs a very constant voltage.

The tuner will not drop out quickly. If battery voltage drops to 5 V , the rest will stop working too i guess

 

[Superduper]

Well, just looked at some schematics and I glanced over them quickly but it appears that.........

The M70 is a 15 volt boombox but the 15volts is dropped to 10.5v by 1st stage regulator and down to 7.5volts by the 2nd stage regulator, which is fed to the tuner.
The M90 is a 15 volt boombox but the 15volts is dropped to 9.4 by the 1st stage regulator and down to 5.2 by the regulator in the tuner.
The M9990 is a 12 volt boombox and looks like all 12 volts is fed to the tuner. This boombox could be sensitive to voltage changes.
The M9994 is a 12 volt boombox but the tuner self regulates it's voltage at 6 volts.
The Sharp GF-777 is a 15 volt boombox but looks like it passes full voltage to the tuner which relies on simple current limiting resistors to protect the IC's. I think this boombox will be quite sensitive to system voltage changes.

 

[monchito]

so norm what you are saying is that ira low voltage is causing his brain to not think correct right

 

[Superduper]

so norm what you are saying is that ira low voltage is causing his brain to not think correct right

You said it Ramon, not me.

But from what I'm seeing, some tuners are regulated at only 5 - 6 volts so it would take a tremendous drop in voltage for the tuner to not see it's normal voltage.

However, there are a few that will see voltage fluctuations since it normally sees battery or near battery voltage so any drop in system voltage will be realized at the tuner as well. Also, he mentioned walkmans. Well, walkmans only get 3volts to begin with and I don't think it could be regulated much less than that since typical silicon semiconductors need .7 volts bias current just to remain in active mode. Any voltage drop across any additional semiconductor will drop another .7 volts as it crosses that junction. Of course germanium semiconductors can work with a little less (.5 or .6 volts) but they are not as common as silicon semiconductors. So I suspect that walkmans will be extremely sensitive to low voltage conditions.

 

[redbenjoe]

norm -- that helps alot -
as some of my boxes are not voltage sensitive

 

[Superduper]

That's correct. If the tuner of a 15 volt box is regulated at 6 volts, that means 6 volts is it's "normal" operating voltage. No matter what the system voltage is, as long as it's a little above 6 volts, the regulator will always supply the necessary voltage to the tuner. Once system voltage goes below 6 volts (or whatever the normal regulated voltage happens to be), then the tuner will finally begin to see lowered voltage. Obviously, it is hard to see a 15volt box being operated at 6 volts or below so such a box will be largely immune to tuner performance deterioration due to voltage loss.

However, if a tuner normally sees battery voltage or is regulated anywhere near battery voltage, then a drop in system voltage due to exhausted batteries will mean the tuner won't see the voltage it is designed for, and therefore, performance will suffer..... especially in the MPX (stereo) decoder circuitry.

So the bottom line is that the greater the voltage differential between the system voltage and normally regulated tuner operating voltage, the greater the immunity to tuner performance degradations from diminished battery voltage.

And inversely, the smaller the difference between normal system voltage and normal tuner operating voltage, the more prone that tuner will be to suffer from lower voltage.

So every boombox depending upon it's design will react and perform differently.

 

[jaetee]

wow, great info here... Thanks SD & Ira for putting this into perspective...

Hey monchito, where did you snag that pic of Ira trying to listen to his radio that you are using as your avatar?

 

[monchito]

wow, great info here... Thanks SD & Ira for putting this into perspective...

Hey monchito, where did you snag that pic of Ira trying to listen to his radio that you are using as your avatar?

jt its a lonnnnnnnng story