Hi all. First time poster, long timer lurker.
I am building a circuit to supply voltage to an electret mic to input to a standard PC sound card but its been too long since I learned electrical theory 😕 I need to figure out the resistor and capacitor values for the circuit below.
V=9.34v supplied. Mic can accept a range of 8-16v.
R=I understand this determines the mic impedance. According to the internet, PC sound cards accept 300ohm (I could be wrong)
C=Used for blocking DC voltage back to the sound card.
I am building a circuit to supply voltage to an electret mic to input to a standard PC sound card but its been too long since I learned electrical theory 😕 I need to figure out the resistor and capacitor values for the circuit below.
V=9.34v supplied. Mic can accept a range of 8-16v.
R=I understand this determines the mic impedance. According to the internet, PC sound cards accept 300ohm (I could be wrong)
C=Used for blocking DC voltage back to the sound card.
Looks like you are using a PP3 type dry cell.
The load resistor can be anywhere from 1k to 15k. The voltage can be 1.5volts or 15volts as it is not critical. Some professional PA systems use 48volts 'Phantom Power' and 68k load resistors.
Noise will be reduced if a decoupling capacitor is used for the supply voltage as batteries are notoriously noisy. I would choose 47nF for the coupling capacitor and 100nF decoupling.
The load resistor can be anywhere from 1k to 15k. The voltage can be 1.5volts or 15volts as it is not critical. Some professional PA systems use 48volts 'Phantom Power' and 68k load resistors.
Noise will be reduced if a decoupling capacitor is used for the supply voltage as batteries are notoriously noisy. I would choose 47nF for the coupling capacitor and 100nF decoupling.
Thanks Jon. Voltage is being supplied from a USB 5v/9v step up module.
I'm not sure what the mic model is. Its part of a Sennheiser aviation headset with poor technical data available.
47nF is WAY too low a value for a coupling capacitor---that will roll off the bass response far more than necessary. It's hard to say what the input impedance of your particular sound card is, but many microphone preamps are on the order of 1-2KΩ; that would necessitate a coupler of at least 10uF. 100nF is good for the power supply decouple/bypass.
Professional condenser microphones use a balanced connection (positive signal, negative signal, ground) with well-matched 6.8 kohm resistors from the two signal lines to a clean 48 V supply. I don't think that has anything to do with this two-pin electret microphone.
Two-pin electret microphone datasheets usually specify a 2.2 kohm resistor to a supply anywhere between 1 V and 10 V. The supply has to be extremely clean, as there is no power supply rejection at all. You could add one or more RC branches to filter off any ripple from the supply, like supply - 1 kohm - 100 uF to ground - 2.2 kohm - microphone.
10 uF is indeed the correct order of magnitude for the coupling capacitor to the sound card.
(By the way, if you want to minimize distortion at the expense of a somewhat higher noise and a more complicated circuit, it is best to connect a two-pin electret microphone to a virtual ground input that just biases the internal FET of the microphone into the triode region. That much reduces the distortion of the FET inside the microphone.)
Two-pin electret microphone datasheets usually specify a 2.2 kohm resistor to a supply anywhere between 1 V and 10 V. The supply has to be extremely clean, as there is no power supply rejection at all. You could add one or more RC branches to filter off any ripple from the supply, like supply - 1 kohm - 100 uF to ground - 2.2 kohm - microphone.
10 uF is indeed the correct order of magnitude for the coupling capacitor to the sound card.
(By the way, if you want to minimize distortion at the expense of a somewhat higher noise and a more complicated circuit, it is best to connect a two-pin electret microphone to a virtual ground input that just biases the internal FET of the microphone into the triode region. That much reduces the distortion of the FET inside the microphone.)
Just wanted to report: I followed your suggestions on capacitor values with success. Thank you!