[sdiy] protecting line level inputs

[Peter Grenader]

A couple of two-part solutions:

A) If you can live with 5.1 volts, I suggest a zener with a current limiting
resistor.  Current limiter is key or else it'll go POP (zener).

B)  Set up an attenuator using a pot to ground.  Dial the amplitude that
works for you, measure that resistance of the pot and replace with a voltage
divider.

- P


Cynthia Webster wrote:

> on 10/20/04 9:19 AM, Theo at t.hogers at home.nl wrote:
> 
>> Diodes from signal to the power rails (both + and - supply).
>> This limits the signal voltage to rails+diode drop.
>> Usually rails + 0,6V is save, therefore run of the mill 1N4148 are ok.
>> And for critical stuff Schottky offers a rails + 0.25V way out.
>> 
>> HTH
>> Theo
>> 
>> 
>> ----- Original Message -----
>> From: <modraj at msoe.edu>
>> To: <synthdiy at sdiy.org>
>> Sent: Wednesday, October 20, 2004 3:33 PM
>> Subject: [sdiy] protecting line level inputs
>> 
>> 
>>> SynthDIY:
>>> I have determined through experiment that my mixer does not like +/- 15
>>> volt spikes (because now it's broken).
>>> What's the best way to send signals from prototype circuits (like a random
>>> spike generator) to a line level input (zener diodes, pre-amplifier)? What
>>> is the maximum +/- voltage that these can handle?
>>> - Justin
>> 
> 
> Hi Justin!
> 
> I solved a similar problem the other day with an interesting solution.
> 
> I was getting hot spikes from a circuit but wanted to limit the output
> from +15V down to a solid + 5 Volt Gate output, I didn't have the right
> zener, so I put a 5 volt Voltage Regulator before the output jack and it
> worked perfectly, (and added all sorts of short circuit protection in
> the process...)  This would not work for an audio signal though :)
> 
> Naturally, I'd always thought of voltage Regulators as a constant voltage
> level device only, it was a surprise to me that it handled momentary
> control voltage swings and rapid pulses with ease!
> 
> One of those quickie "what if?" solutions that worked LOL!
> 
> Cynthia
>