[sdiy] protecting line level inputs

[Oakley Sound]

> I have determined through experiment that my mixer does not like +/-
15 volt spikes (because now it's broken).

Any decent mixer should not suffer with +/-15V input signals. After all,
most pro-audio desks can actually output this level of signal as part of
normal, albeit its upper limit of, operation.

My recommendation is to use a 11:1 attneuator. This can be as simple as
a 10K resistor in series with the signal and a 1K resistor in parallel
with the input socket. These two resistors will act as to attenuate the
signal down to very safe level. I would also add perhaps a 1uF non polar
cap [like polyester] in series with the 10K resistor to block any DC
too.

The other idea of zeners is good, but this can add non linearities, and
without a scope you might not know this.

Regards,

Tony Allgood                           www.oakleysound.com

Oakley Modular Synthesisers      Penrith, Cumbria, England