Couple of questions (SS Amp Related)

[anti-idiot]

Hi, i was checking my SS Amp (Marshall MG15CDR) and i noticed it has 2 diodes at the input of the opamp, pretty much like the input of this amp:

http://www.drtube.com/schematics/marshall/3315-preamp.gif

what are they for? (since the opamps are using bipolar supply) i supposed it was for lowering the threshold...


Second question: does anybody knows any 4-channel switching (non-secuential) pretty much like MesaBoogie Quad Preamp (but without the tons of ICs). I'm gonna make a "quad-preamp" (Clean/Crunch+Overdrive/Distortion) and i was (originally) thinkin' bout using relays, but my options will be kinda limited (Ch1 or Ch2)

[frankclarke]

ESD protection. http://www.automotivedesignline.com/howto/196602756
Ampage is good for relay switching tube amps.

[R.G.]

See "What are all those parts for?" and "When Good Opamps Go Bad" at GEO.

They're input protection diodes.

[anti-idiot]

thanx RG, i didn't thought bout GEO since i was lookin for some images of the diode protection (english is not my thing, yo hablo español).
thanx frank, i'll look some ampage schematics...