The 7805 / 7905 is well-known fixed voltage regulators. (sidenote - if you don't know what 7805 is, then you should not even consider moding the card, you are messing with things w/o knowing what they are, that could end up pretty bad...) However their output voltage can be easily adjusted by just a simple two resistors voltage divider, increasing the voltage on the chip "common ground" and since it trying to stabilize the voltage to the fixed amount between output and common ground, then you can easily regulate/modify the output voltage...
Just check the datasheed for many and many and many examples how to use these fantastic chips:
http://www.st.com/stonline/products/...143/l7812c.pdf
Bias to opamp? I would say opamp operating voltage...
And yes and no.
Yes for the calculation of the minimal operating voltage, but you have that mentioned already in the pdf datasheet I linked there. Please read materials first, before asking.
No for the results. Powering opamp from +/- voltage yield better results, especially in higher frequency of the audio spectrum.
And since these opamps are in the pre-amp stage, then there anything has a HUGE impact on the results.
Hope that helps.
PS: Digi-key stated the obvious quite clearly too:
http://search.digikey.com/scripts/Dk...AD8599&x=0&y=0
You see? Single voltage - 9 V ~ 36 V, required. But - double voltage supply: ±4.5 V ~ 18 V
I hope all is clear now.
PS2. I somewhere suggested that the input opamp (MC33078) should be replaced too. Good choice seems to be again the AD8599 - but hold your horses! This time the opamp is powered from +5V only (the leg 8), leg 4 is NOT connected to the -5V as all other opamps there - but to ground. Hence this one is getting only 5V. AD8599 require by specs at least 9V. I'm affraid that it will not work good there... time to find another opamp, +5V capable one