11-11-2023, 06:00 PM
(This post was last modified: 11-11-2023, 06:04 PM by Mike Watterson.)
I found an older electret mic that had had a transformer robbed out of it. So I cut away the plastic for the springy negative end mount and fitted a plastic spacer behind. Wired that to the centre of coax cable and a 2.2 kΩ across the coax cable. Wired outer to wire going to can of electret. Wired "live" of capsule to switch and switch to positive terminal. Added some glue and let it set. Fitted two tested OK N/Lady/LR1 cells (about 1.58V each). With the switch on I get -1.06 V on the tip to sleeve of the jack plug, thus about 480 μA current, so approximately 1,600 hours run time (66.7 days), assuming 800 mAH on the small N/Lady/LR1 cells (Alkaline AA are about 2,700 mAH). That's about 200 off 8 hour days!
I suspect older capsules are about 0.5mA Id and newer ones are about 0.3 mA or less. I have a drawer full of standard and miniature ECM capsules I can test.
I'm thinking that the 680 Ω load on the other two doesn't matter as the maximum approximately 100mV RMS limit caused by that would be a massive sound level?
Curiously this older mic (early 1990s?) has a lower sensitivity.
I suspect older capsules are about 0.5mA Id and newer ones are about 0.3 mA or less. I have a drawer full of standard and miniature ECM capsules I can test.
I'm thinking that the 680 Ω load on the other two doesn't matter as the maximum approximately 100mV RMS limit caused by that would be a massive sound level?
Curiously this older mic (early 1990s?) has a lower sensitivity.
