Bypassing the FET inside electrec mic, not just connecting as source follower. - Page 1
Forum section: electronics / projects

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: September 25, 2022, 04:03:49 pm
content: I was thinking if it could be possible to for example put like 40-50V across the fet to short it, and then effectively connect to the electret capsule directly.the electret element probably would be blown up in the process unless I first separate the connection between source and the case.what do you think?

author: TimFox
author_rank: Super Contributor
timestamp: September 25, 2022, 04:12:48 pm
content: Capacitor microphones, including electrets (which do not need external voltage to polarize the capacitor), can be modeled as a voltage source (from the acoustic input) in series with a not-too-huge capacitor.To get decent response in the audio range, they require a high resistance load, in parallel with a capacitance much less than that of the microphone.Without a JFET (or cathode follower) to buffer the actual load, the output will be disappointing.

author: Zero999
author_rank: Super Contributor
timestamp: September 25, 2022, 04:47:47 pm
content: Why do your want one without a J-FET?Destroying it with overvoltage is a bad idea. It's possible to remove the J-FET. I've done it before, because I wanted to try using it as an ultrasonic transducer. It didn't work too well.

author: Zero999
author_rank: Super Contributor
timestamp: September 25, 2022, 08:43:57 pm
content: Quote from: ELS122 on September 25, 2022, 04:57:05 pmNot in the ones I've opened. Choose the largest microphone available. Cut away at the crimping at the back and the disc at the back will fall off, along with the J-FET.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: September 28, 2022, 04:31:58 pm
content: IMO, the best option is to just buy a decent condenser mic capsule. The prices have come down and you can get anything from a 1/4" measuring mic to a 1" studio mic. There's a group of mic builders on groups.io-https://groups.io/g/MicBuilders/messages

author: Zero999
author_rank: Super Contributor
timestamp: September 28, 2022, 04:48:57 pm
content: Quote from: ELS122 on September 28, 2022, 09:56:35 amThe question is why? I hope you're aware of the fact the output impedance is very high, especially athighlowfrequencies. It's equivalent to around 5pF. The capacitance of a short length of cable will greatly attenuate the signal. This is why the J-FET is integrated into the microphone capsule in the first place.In my case, I removed the J-FET so I could connect it to an oscillator to generate ultrasound. It didn't work very will. I'd probably need to run it at a couple of hundred volts peak, to generate a decent output, which I didn't try, as it would've probably smoked.

author: Zero999
author_rank: Super Contributor
timestamp: September 28, 2022, 09:24:58 pm
content: Quote from: ELS122 on September 28, 2022, 05:07:45 pmThe FET is common source. It is not a follower.An electret is the electrostatic equivalent of a permanent magnet. The whole point of using an electrect microphone is there's no need for a high voltage power supply to bias it. The principle is similar to using a permanent magnet in a dynamic microphone, rather than an electromagnet.