external audio input module

[Matt Haines]

>     I would put a shunt series reverse pair of zeners right on the output
>     of the op amp to ground.  You would pick the max voltage you want
>     (hard limit) by adding the forward voltage drop of a diode (0.7V) plus
>     the zener voltage of the diodes.  For example, picking a limit of
>     6.8V, you would pick 5.1V zeners.
>

by 'series reverse pair' you mean the folllowing, right?

        o----->|---|<------GND

>     A nice feature many commercial companies use is to put an LED
>     somewhere in there so that it turns on when clipping starts.  If you
>     can find a bidirectional LED (one that lights in both directions) you
>     can out it in series with your zener pair and maybe a 1K resistor (to
>     limit current to the LED).  So when the zeners start to hard limit (or
>     turn on and pass current), the LED will light.  I don't know if such
>     an LED exists but I know the LED technology has come a long way.


If I throw another diode in there, and a resistor as well, that changes
what I need for zener values, yes?


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Matt Haines  haines at apc.net         .       .       .       .
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Moonlight, Muzak, Knick-Knack, Paddywack