Microphone Preamp

C101, C102, and C103

there to cancel out frequencies above audio before they are amplified.

SW101

there to turn on or off the +48V phantom power.

R101

there to isolate multiple channels from each other.

R102 and R104

here to supply +48V to the Hot and Cold audio paths without shorting them. Their value is set so that, if they are shorted to GND, only 14mA of current is drawn from the +48V supply.

C100

there to filter any AC from the +48V supply.

R103

sets the input impedance of the circuit.

C104 and C105

block DC (+48V) from getting to the inputs of the mic preamplifier I.C. They could also be used to affect frequency response as high pass filters.

D101-D104

limit the spikes created when +48V is turned ON (+48 spike) or OFF (-48V spike) by limiting the peak to roughly +/-15.5V.

• They would also limit very large line level signals if connected to the Mic input.

R105 & R106

there as current limiting resistors to reduce current when those spikes are being limited.

SW102

Selects either the microphone input path (through R105/R106, etc.)
or the line input path (through R107 & R108).

SW103

Swaps the Hot and Cold signal paths to invert the polarity of the audio signal.

R112 and R113

set the common-mode input impedance.

R114 and R115

isolate the I.C. from the power supply rails to protect other I.C.s.

C106 and C107

Filter noise from +/-15V power rails.

VR101 and R110

combine to set the preamplifier gain. Together they approximate a reverse logarithmic taper potentiometer which is required for the preamplifier.

R111

Sets the maximum gain of the preamplifier.

C108

Blocks DC from VR101/R110.

U101

the microphone preamplifier I.C. and it's purpose is to amplify microphone signal to line level

C109

Block DC from getting into or out of the microphone preamplifier I.C.

Differential Mode

output is the difference between the hot and cold signal paths. signals that are different between hot and cold end up as higher voltages at the output

Common mode

signals that are the same on both hot and cold are connected out and appear as lower voltages at the output

C102 is in the circuit to  

Get rid of above audio frequencies

R102 and R104 have a value of 6.8kΩ because  

it prevents too much current from flowing when there is a short

What component(s) has(have) the largest part in setting the differential mode input impedance?

R103

What is the purpose of C104 and C105?

Block DC

What is the purpose of D101-D104?
or
What are the purposes of D101-D104?

limit spikes from +48V to +15.5V

limit spikes from +48V to -15.5V

Phantom power would best be described as  

common mode

Sound from the microphone would best be described as      

differential mode

Noise added as the signal is transferred through a microphone cable would best be described as

common mode

Which of the following has the function of setting the common mode input impedance for above audio frequencies?

C101

Which of the following has the function of setting the common mode input impedance for audio frequencies?

R113

preamp

amplfies signal from a mic up to line level

mic level

-60 - 20 dbu