quick question about the diode in the phase 45

[Sir_Ian]

heres the schem
http://www.tonepad.com/getFile.asp?id=70

Ok, I was looking at the schematic...and I can't quite figure out what the diode is supposed to do.

My best guess is that it is somehow helping to set the reference voltage. I know the trimpot helps set the voltage, but I thought the diode helps somehow too.

However, the diode is in there "backwards." I'm guessing, somehow electrons are still flowing through it. If it were in the schematic the other way, Vref would almost be a short circuit to ground.

I was also curious if in its current position, the diode helps with reverse polarity protection or not....I see that its not a complete short circuit, because you would still have a 10k resitor. And I know this can't be the SOLE reason because a germanium diode is requested and for reverse polarity protection, you could just use any old diode. Any info or links to good articles where I could read up on this would be much appreciated. (I tried searching the forum, but came up empty handed. My apologies if I simply missed something thats already out there.) Thanks.

[oskar]

My best guess is that it is somehow helping to set the reference voltage.

Bingo. That's the reference for the OP amps. The signal needs this to give it a span in between 0 and 9v as it is otherwise oozing around 0V.
The zener and the 10k to V+ sets the reference.

I know the trimpot helps set the voltage, but I thought the diode helps somehow too.

The trimpot sets the bias for the FETs.

However, the diode is in there "backwards." I'm guessing, somehow electrons are still flowing through it. If it were in the schematic the other way, Vref would almost be a short circuit to ground.

It's a 4.7V Zener diode. It works as a normal diode in the other way but it has a lower reversed breakdown voltage. It's used a lot for reference voltages and clipping/protection.