Omni i/o 2 channel preamp to pc a/d
 

No abuse apparently, owner plugged in a new microphone and blew one channel.
Seems to have knocked out expensive instumention op-amp ( comparing the 2 ).
I don't like the look of the electrolytic at the input, no input dropper
resitor and a 48V
phantom supply involved. Anyone any ideas ? don't fancy spending out on
an expensive Burr Brown IC if it is only going to happen again.
I've not often dealt with kit with phantom supplies - can any one
direct to a resource of generic probs associated with 48V on signal inputs?

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

"N Cook" wrote in message
...
No abuse apparently, owner plugged in a new microphone and blew one
channel.
Seems to have knocked out expensive instumention op-amp ( comparing the
2 ).
I don't like the look of the electrolytic at the input, no input dropper
resitor and a 48V
phantom supply involved. Anyone any ideas ? don't fancy spending out on
an expensive Burr Brown IC if it is only going to happen again.
I've not often dealt with kit with phantom supplies - can any one
direct to a resource of generic probs associated with 48V on signal
inputs?

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/





There is 2 6.8K resistors from the 48V line to each of the balanced mike
lines , so protecting the phantom supply.
Each of these mike lines is connected via a 10uF/100V electrolytic directly
to + and - inputs of the op-amp.
So if a short to ground at the mike then the +48V side of the electrolytic
goes to 0V and the other side must go to -48V
or at least try to , op-amp supplies +-15V.

Modification of clamping diodes at the + and - opamp inputs?