Le 16/06/2022 ¨¤ 12:09, thet a ¨¦crit?:
There are two scenarios for connecting a single sided capsule with external polarisation.
1. In a typical LDC you would normally connect one side of the capsule to the polarisation voltage and take signal from the other side. Neither side is DC grounded, although the polarised side is at AC ground.
2. In most SDC mics the backplate is grounded through the body and you have to apply polarisation voltage to the signal side of the capsule.
This requires a second 1G resistor and a blocking cap.
It lowers the input impedance of the headmp to 500M instead of 1G and puts an extra capacitor in the signal path.
So it seems like an obviously inferior arrangement.
So why do people do it? Why not make the effort for SDCs to have a 3 contact connection for removable capsules.
Probably a matter of tooling.
Would using 2G resistors in both positions help or cause other problems?
Yes. There are a few examples that use higher values. Although with higher values, the circuit becomes extremely vulnerable to moisture. FET gate leakage may also be an issue.
Does it even matter that much? If it doesn't matter why not use 500M resistors in scenario 1?
It does. The perceived noise level is proportional to the cut-off frequency of the HPF constituted by the capsule capacitance and the gate and bias resistors in parallels.
My motivation for asking is that I'm building a mic where I have a choice between making the capsules interchangeable but using a #2 polarisation scheme, or fixing the one capsule in place with a #1 polarisation scheme.
