On 25/10/2011 19:14, Bob Blick wrote:
> It's the transient that occurs during the plugging-in. Typically an RCA
> or phone plug contacts a signal to ground or a signal to signal before
> the ground to ground connection is made. Imagine connecting the signal
> input of a grounded device to the ground of a laptop computer, one that
> has a two-prong power plug. It already is capacitively coupled, the EMI
> circuitry of the laptop's power adapter has a capacitor from AC center
> tap to DC ground. So you are shoving 60 VAC (120 in 240 volt lands) into
> a poor little opamp. It's very lively.
>
> Eventually the grounds of the two systems make contact and things
> usually are fine from then on. Usually.

The "standard" couple of diodes with current limiting series input=20
resistor is what I've usually seen implemented in audio inputs.
This page http://www.angelfire.com/sd/paulkemble/sound7.html (input=20
protection right at the bottom) describes a few methods.
Of course you could go for e.g. an XLR connector to avoid the temporary=20
short  problem altogether,

--=20
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