Audio Op Amp Questions

[YaranAyr]

I have questions about Op Amps. Please refer to the attached image.

Figure 1 - Inverting Op Amp.
I see dozens of mixer/audio amp schematics that show a wide range of resistor values for Rvol, Ri, and Rf – from Rvol & Ri =1K to 100K
And Rf= 10K to 1M.
I understand that the gain ratio is Rf/Ri.
I DON’T UNDERSTAND the reason for the wide range of values from schematic to schematic..
1. What is Ri for? Impedance?
2. What is Rvol? Just Volume? Or does it create an output impedance for the previous Op Amp stage (if it’s output wasn’t capacitively coupled?)
3. What is the value relationship between Rvol and Ri?

Figure 2. – Single Volt Supply Inverting Op Amp.
I understand that Rdiv1 and Rdiv2 should be equal values to split the Vcc in half.
4. What is the difference between having smaller values as opposed to having larger values for Rdiv1 & Rdiv2?
5. Is there any interrelationship between these two dividers and the rest of the Resistors in the circuit that would dictate their values?
6. If it didn’t matter, would it be beneficial to use larger values just for the sake of having less battery drain through them?

I would like to make a "Universal" Audio Mixer with mic/guitar inputs to line outputs supplied with a single 9.6V supply.
7. Would R values change if I hooked up a single 12V supply?
8. Is there any advantage of having a –4.8V - Ground - +4.8V supply (other than not having to have Voltage dividers?)
9. Any suggestions for a value for Ri for guitars and microphones?
Answers to these questions and any other info/suggestions are appreciated greatly.

 

[Nigel Goodwin]

Essentially resistor values are for setting input impedance and gain, supply voltage has no bearing on it.

Where supply voltage does matter (and a LOT) is in the headroom - only a 9.6V supply is really pretty low and limiting. For a portable system at least +/-9.6V would be better, but usually either +/12V or +/-15V is used.

If the supply voltage is too low, then (assuming you pick opamps that will work that low!) you are seriously limited in signal and output levels, which in turn makes it all a lot noisier.

 

[audioguru]

A dual-polarity supply amplifier has coupling capacitors with zero volts across them so they do not cause a loud POP noise when the power supply is turned on because they do not charge.

But a single-polarity supply amplifier has an input coupling capacitor, output coupling capacitor and a filter for the half-supply reference voltage capacitor that all quickly charge when the power supply is turned on which makes a loud POP noise.
If your circuit uses very high value capacitors so that they charge slowly and avoid the POP, then the amplifier takes a long time to turn on and turn off and produces severe distortion during the charging and discharging times.