Opamp bias with diodes?

[d95err]

I'm looking at a schematic for an opamp based effect loop I'm thinking about installing in a tube amp I'm building.

Schematic: (Click on the image to get a bigger view)
http://forum.musikding.de/gallery/displayimage.php?album=124&pos=6

I'm only interested in the effect loop part, not the reverb for now. It is basically two inverting opamp gain stages with a bipolar supply. That's the easy part. What I don't get is - what are the two diodes between the opamps going to the + and - supply doing? Is it some kind of bias function? I thought bias wouldn't be necessary here, since it's a bipolar supply.

[Steben]

It serves several causes. Most important I guess is firstly to limit the differential voltage between the two inputs regarding the opamp itself, I thought I read something about it. Secondly, it also functions as a signal clipper.

EDIT: oh no, it's THAT kind of connection. It's just a plain signal clipper (opposite polarity than power) in quiescent mode there is no current through the diodes.

[johngreene]

They are protection diodes to protect the input of the opamp from a signal that exceeds the supply rails from the parallel return.

--john