Howdy folks - couple of questions about electret condenser mics, the miniature types in specific.
If I understand, an electret mic doesn't need external power to bias the transducer element (bias is provided by the electret material), but most often does require power as most have a built-in JFET preamp stage. This is versus legacy condenser mics (Neumann U67 etc) which require power to bias both the element, as well as run the preamp.
Ok so far?
But looking at a typical schematic for a mini electret mic, you can see that there's no bias network for the FET preamp, only a current limiting / load resistor in series with the Vcc. Do the diagrams omit the other bias resistors, or does it work without them? Assuming a standard n-channel JFET, if there's no bias network, wouldn't any positive-going signal put the device into a non-linear gate current state? How does it manage a reasonable, low-distortion output if there's no bias network?
ETA: Err.. wait a moment.. lol! Is the static electret voltage sufficient to adequately bias the gate negative? I assumed it was only a few tens of uV.. how large is it? The mic symbol doesn't indicate any polarity for the electret, which is why I missed this..
If I understand, an electret mic doesn't need external power to bias the transducer element (bias is provided by the electret material), but most often does require power as most have a built-in JFET preamp stage. This is versus legacy condenser mics (Neumann U67 etc) which require power to bias both the element, as well as run the preamp.
Ok so far?
But looking at a typical schematic for a mini electret mic, you can see that there's no bias network for the FET preamp, only a current limiting / load resistor in series with the Vcc. Do the diagrams omit the other bias resistors, or does it work without them? Assuming a standard n-channel JFET, if there's no bias network, wouldn't any positive-going signal put the device into a non-linear gate current state? How does it manage a reasonable, low-distortion output if there's no bias network?
ETA: Err.. wait a moment.. lol! Is the static electret voltage sufficient to adequately bias the gate negative? I assumed it was only a few tens of uV.. how large is it? The mic symbol doesn't indicate any polarity for the electret, which is why I missed this..
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Here is a jfet intended for electrets. Note that there is a high value gate - source resistor built in
http://www.onsemi.com/pub/Collateral/ENA1616-D.PDF
http://www.onsemi.com/pub/Collateral/ENA1616-D.PDF
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