RuudNL said:
Yes, this is a very common circuit used in several Chinese microphones!
Exactly and in fact it's slightly modified version of modified schoeps converter used in many chinese microphones.
midwayfair said:
I recognize that one from the CAD circuit. Figure 8 is set to 30V, cardiod is the full 60V, right?
I don't remember what values were used in several chinese microphones, but i build that type of converter to use with higher voltages.
Anyway even if it would be used with 30V/60V, then cardioid should be 30V and figure of eight 60V.
Or just fig 8 need higher voltage.
Look at schematic, R16/R17 form voltage divider for backplate polarisation, then look at the switch SW3.
For cardioid SW3 setup, R15/R19 form divider for back diaphragm polarisation - now backplate and back diaphragm have the same potential, which is true for cardioid pattern with that type of input toplogy.
For fig 8 SW3 have no connection so on the back diaphragm polarisation voltage is doubled in reference to the backplate voltage - it's correct for 8 pattern.
I didn't checked omni option, looks strange like a short, but maybe it works
Am using that type of converter with "true" cardioid, omni without connection to the polarisation voltage or ground so the only polarisation voltage at the back diaphragm is for fig 8.
Anyway higher polarisation voltage can be done same way as in schoeps or chinese "schoeps" converter.
Adding pot like in original schoeps circuit is usefull but also you can rise zener diode voltage value.
Note that the main difference between these converters is that the cad have two additional diodes for multiplier