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Old 9th January 2011, 02:24 PM   #1
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Default Homemade electret mic power supply

I am attempting to make a power supply for a homemade electret mic connected to a 1/4 inch mono jack, which will then be plugged into the power supply. The recipe comes from the Nicolas collins "art of hardware hacking book". A 9v battery is run to a mono socket, then to a 2.2k resister, then a .1uf capacitor and another mono socket. Each mono socket has two soldering points and I am unsure of which goes to the tip and which goes to the sleeve. I am also uncertain of whether or not the socket will run the power from the 9v to the 1/4 inch plug thus powering the electret element. Sometimes, when I blow into the capacitor it seems to pick up sound like a contact mic, does that mean it is receiving power and could be damaged? Or simply functioning that way because it is not recieving power??
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Old 10th January 2011, 03:12 AM   #2
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Quote:
Originally Posted by dusty summers View Post
I am attempting to make a power supply for a homemade electret mic connected to a 1/4 inch mono jack, which will then be plugged into the power supply. The recipe comes from the Nicolas collins "art of hardware hacking book". A 9v battery is run to a mono socket, then to a 2.2k resister, then a .1uf capacitor and another mono socket. Each mono socket has two soldering points and I am unsure of which goes to the tip and which goes to the sleeve. I am also uncertain of whether or not the socket will run the power from the 9v to the 1/4 inch plug thus powering the electret element. Sometimes, when I blow into the capacitor it seems to pick up sound like a contact mic, does that mean it is receiving power and could be damaged? Or simply functioning that way because it is not recieving power??



This is the way your jack sockets and components should be wired. You should be able to determine which contact is tip and which is sleeve by examining the jack sockets.


If you are still uncertain about anything, feel free to ask again.

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Old 10th January 2011, 07:28 AM   #3
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An electret needs no power supply. It's built in. A condenser/capacitor microphone needs a 'phantom' supply but an electret is just that. It's a plastic with a built in charge.
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Old 10th January 2011, 08:08 AM   #4
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Quote:
Originally Posted by bob91343 View Post
An electret needs no power supply. It's built in. A condenser/capacitor microphone needs a 'phantom' supply but an electret is just that. It's a plastic with a built in charge.
I have never seen just the electret mic available on it's own. Don't they always include an FET buffer?

http://en.wikipedia.org/wiki/Electret_microphone
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Old 11th January 2011, 12:26 PM   #5
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Most of the small panasonic types have a built in fet. The fet is specially designed for that purpose and has increased gate leakage to bias the capsule.

For best results modify the internal circuit from common source to common drain.

You can buy electret capsules without a fet from places like Transound.
These can give very nice performance with a good low noise fet and resistor biasing.

Les
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Old 23rd May 2013, 02:11 PM   #6
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Quote:
Originally Posted by Huntingdon 361 View Post


If you are still uncertain about anything, feel free to ask again.

Click the image to open in full size.
What if i want to use a power supply instead of a battery? A stabilised supply using a lm317.. Can i still use this schematic but in the place of the battery, could i use the psu?..

And also, if this is possible, can i power, with the same psu , 4 total mics? Or should i build separate psu for each mic?..
Thanks in advance!
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Old 23rd May 2013, 05:31 PM   #7
Mooly is offline Mooly  United Kingdom
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One PSU will power thousands of capsules

PSU's have a low impedance at AC so no problems with interaction. Although FET capsules work on 1.5 volts, its worth consulting data sheets to see the recommended voltage range as many will accept much more with consequently better performance.
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Old 23rd May 2013, 05:33 PM   #8
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perfect..any ideas on what R an C might be?..i mean what value...
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Old 23rd May 2013, 05:43 PM   #9
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Depends on the capsule, the supply voltage and the impedance of the following stage but values around 1uf for the cap and 1K5 to 8K2 would be in the right region for supplies of say 1.5 to 9 volts.
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Old 23rd May 2013, 06:02 PM   #10
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perfect...thanks for all the info. as soon as i try it i ll post..
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