Behringer ADA8000 schematic question

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chr1s

Well-known member
Joined
Apr 5, 2008
Messages
48
Location
Germany
Refering to the schematic from gyraf's page there are two diodes (bav103) at the input differential stage. I think I understand the other parts of the schematic but I have no clue why these diodes are there. They seem to clamp the differential stage's outputs to the following opamp against the negative rail if the output voltage falls below that rail voltage. But I can't see any way that happening.

So, what do they do?


Chris
 
They appear to be clamps to prevent the TL074 inputs from swinging more negative than a diode below - supply. Some bifets have been known to reverse output polarity under such circumstances.

You have to bang the input pretty good to do that, so I suspect they are anticipating a transient short to an input that is charged up to phantom voltage (perhaps in a patch bay). Personally I'd add clamps across the input devices (to prevent zenering), but who knows who behringer was copying. Not me.

JR

 
JohnRoberts said:
You have to bang the input pretty good to do that, so I suspect they are anticipating a transient short to an input that is charged up to phantom voltage (perhaps in a patch bay). Personally I'd add clamps across the input devices (to prevent zenering), but who knows who behringer was copying. Not me.
I didn't consider the inputs, but that makes sense. Thanks for the explanation.


Chris
 

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