Here's my incomplete single board 4 mic 2 output draft circuit.
the capsule power is not connected yet. it could share the opamp V+ or it could use a series power configuration.
this version the power supply is shared between the left and right hand channels and a dual opamp is used
However if two separate boards are required for left and right hands then the circuit could be halved - a single opamp could be used on each board with it's own power supply.
putting it all on? one board is less components overall - but requires a wire through the bellows.
separate boards might be more applicable to other instruments with two mics.
