Pimped Alice Electret Microphone - No change in voltage with pot adjustment?

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T-Squared

New member
Joined
Dec 13, 2021
Messages
2
Location
San Antonio, TX
I recently rebuilt a microphone (which I will rebuild again as a stereo mic), with a 2015 Pimped Alice schematic: Modify a Cheap LDC Condenser Microphone. My microphone seems to work just fine, but I'm not sure of the purpose of the 1MOhm pot, since when 48v phantom power is applied, the voltage does not change when a multimeter measures any of the components. (Any measured voltage hovers around 5v or so when active.)
 
Are you 100000% sure you were measuring the voltage on the JFET drain? And/or that all the components on the board are soldered in correctly, and are not faulty?
 
Hi T-Squared,

welcome here. what version of the PA circuit did you build? Normally, there are two-three voltages you have to determine: VCC, SRC and if you are using the vs. 5.6 including the DC-DC converter you can also determine the Pol-Voltage.
If you use the DC-DC converter, you may want to check the alignment of your inductors, as I read that can affect the efficiency of the DCDC conversion. Maybe you can post a picture of your PCB here?
Other than that, I could not reach the voltages at VCC either (they were around 8-9 V in my case). So I adjusted SRC to 1/4 of that value and the mic works really nice (Dual Output Microphone: 2x Schoeps Circuit + K87 capsule BM-800 Donor Body)). Maybe you find something useful in the documentation of the built.

Best wishes and nice holidays,
Michael
 
If you measure on the drain of the FET, you should see a variation of the voltage when you rotate the trimpot.
If not, you are measuring at the wrong point, or there is an error in the construction.
But the microphone seems to work, from what I read...
 
I had planned to use an LDC, but I got the wrong PCB type, and I'm working on a video that I hope to have out on New Year's Day, so my time is very short.

My PCB is the initial iteration of the Pimped Alice circuit for the Transsound pre-charged capsule (Or whatever comes with a BM-800 microphone), laid out by Homer Leal: (In Step 3 of this Instructable:) Build the MS Alice Stereo Microphone

I did measure at several points, including all points of the JFET, but no change in voltage was observed. Strangely, despite others saying to float the lead of the JFET gate, I don't have any problem with noise when I soldered it in the board, and the sound is very clean!
 

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