My project requires me to have sixteen opamps all running off a single twelve volt supply. They are audio buffers if it matters. Any way, I am using a voltage divider to get 6 volts which I am using as a reference voltage with which to bias the opamps at 1/2 the supply voltage. I have never fed so many opamp stages with a single reference voltage before, so I have questions.
First, my final design will run off the mains, and as such, I will easily be able to switch to a true bipolar supply for the opamps. For now, I'm running off of my bench supply, and I only have D.C. to work with. I realize I could use a D.C. to D.C. converter of some sort to get a negative voltage, but that sounds overly complicated considering I will have AC at my disposal in the eventual design. I've never used a D.C. to D.C. converter before either, so I'm open to being sold on the idea.
But if I stick to the original plan, I have a question. What is the best way to distribute this reference voltage to each opamp? Currently I have an individual 1 meg resistor for each section. So imagine an opamp wired as a follower, with the six volts fed through a 1 meg resistor to the non-inverting input. This is what I have now, and it seems to work. It just seems inefficient to have so many resistors. Also, the best value for this resistor seems hard for me to determine. I think my main purpose is to keep the audio signals from interacting. To me that says go big. Noise control seems to say the opposite. Also, I had assumed that with the massively high input impedance of the opamp input, I could use just about any value without the 6 volts being attenuated. This turned out to be incorrect. When I put a smaller resistor in just one section, that section's voltage is lower. Not sure why. My understanding of matters must be off. This seems to imply that maybe there are impedance reasons to consider also.
Any thoughts?