battery powered RIAA preamp question

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Hi!

I am thinking about making my RIAA phono preamp battery powered. The preamp I itin question is ESP project #6 buildt with AD825's. (http://sound.westhost.com/project06.htm)

PSU will be 2x8 LR14 batteries for a +/- 12V supply.

But, now I will never know when the voltage gets too low (under +/- 5V)

What I am thinking is this: There must be some simple way to implement a LED, which turns on when the voltage drops under a certain voltage(say, 6V)? Maybe a zener and a resistor or something?

Any hints/ideas/suggestions would be greatly appreciated...
 
Hello Mad_K,

how about a comparator wired as window comparator? LM339 has 4 comparators in one DIP, for a window comparator you need 2 ot them. Let one input look at a voltage divider with Zener as lower and resistor as upper elements and the other input look at a votlage divider made from two resistors. Tune resistors so that comparator turns Led on if supply voltage drops under 5V.
Should alos be possible with a NE555.
 
sorry Bernard, I was typing while you replied.

-That sounds like a great idea! They have the lm339. I'll have a go at it tomorrow, -now it's time to get some sleep before work again (every day is a weekday:().

PS- What do you think of the battery powered setup I described? I have done some estimates, and it looks like I can have quite a few hours of pure power from those batteries?

PPS- Part of the reason I'm doing this is because I'm building a new passive preamp, and then I came up with this brilliant(?) idea. (The RIAA-pre will go in the same box as the passive pre).
 
Re: Zener Circuit

hagtech said:
Yes, the previous zener circuit is very good and effective. But swap polarity of zener, it is shown backwards. Can't get any more simple that this.

Whoops. My apologies. I drew it up in AutoCAD copying components from an existing circuit. I just copied two bias diodes from a current source and added a couple of lines to make one a zener and one an LED and forgot to flip the zener around.

Thanks for catching that! The illustration's been updated.

se
 
:eek: Awww!

So it is as simple as i suspected...

-So I just stick a zener in series with a resistor and a LED tied to the rails, and then this arrangement stops conducting when the voltage is lower than the zener voltage?

(I know this is the opposite of what I asked, but it does the same. The LED stops lighting when the voltage is too low, rather than light up.)

-Time to have some fun! -Maybe we don't need a christmas tree this year!!:D
 
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