Amplifier Input board Questions

[joakinrox]

Hello guys, So I decided to build a rather ambicious project (for my skill level at least) which is an arduino controlled amplifier and effects bank. Due to the physical layout of the Wooden box I'm planning to put my amp in, I that the design will be composed of 3 main boards:

an effects board (with sockets to connect various interchangeable effects, CMOS or relay switched)
a main board (with my power amp, a Rog's condor cabSim into a cmoy headphone amp)
an input board (where the guitars are connected, the audio sources are selected and the tuner circuit is located)

Right now I'm designing the input board (see the block diagram) with the following design requirements.

-2 audio inputs; for guitar/guitar or guitar and bass (which will be mixed in the main board before going to the power amp)
-The audio sources can be either the cable comming from the instruments, or 2 FM receivers, the sources will be switched by a 4066 CMOS switch.
-The power supply voltage is 0-10 volts, all the logic will be powered from 5 to 10 volts
-Guitar 1 will be preamplified to 5Vpp  and then fed to an analog pin of the microcontroller to tune the guitar
-All boards will be comunicated through an I2C bus


Now, onto the details and my questions:
-What size should the Caps at the buffers/CMOS switches be? (I'm placing 20uF caps in the signal path to avoid messing with the signal, but I don't know if this is too big and would make my signal muddy?
-I read R.G's CMOS switching article, and he places a bias voltage (1/2 of the power supply) at BOTH ends of the 4053 CMOS switch. Is this necessary for the 4066 as well?


-From my understanding, to avoid distortions on the CMOS switch, no current must flow through it. so placing a buffer before and after the CMOS switch would prevent this. So in theory, if I pass my signal through 20 Cmos switches (the amount that the signal would have to pass through in the effects board if I do CMOS switches instead of Relays) but place a buffer before (low impedance output) and after (high impedance output) there should be almost no current transfer, hence no switch-induced distortion. Right?


-About Grounding, due to a requirement of the digital potentiometers I'm going to use, I decided to power all the logic of my design from 10-5 volts, while analog parts (effects and power amp) will run on 0-10 volts.  This would make my digital "ground" 5 volts, and my analog "ground" 0 volts. at the power supply end, I'm thinking of using the circuit shown here:
http://www.diyaudio.com/forums/solid-state/234665-virtual-ground-regulated-rail-splitter.html to provide me with a solid digital ground at the power supply end. Will this bring me any noise issues?


-At the output of the CMOS switches from guitar 1, I'm placing this amplifier circuit (Powered with 0-10 Volts) to take the guitar signal to a 5Vpp range so the arduino can detect the frequency. I placed these clipping diodes to avoid hitting over 5Vpp and damage the arduino, do I need to place a resistor between the diodes and ground to avoid high currents?.  Do I need to bias the +Input at 1/2 the op-amp's supply? Should the votage at the end of the resistor attached to the -input be 0V, or 1/2 power supply(5V)? I tried simulating this circuit in Proteus, but everything I tried gave me a perfect output, which I'm sure won't be the case in the real world.



-I'm using these OpAmp arrangement to provide Vref for the Cmos Switches because I read that it is more stable than a regular resistor divider. Would this arrangement also need the Bypass cap between 1/2 supply and 0 Volts as is usually done in effect circuits?




Thanks in advance for the help!