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Strange Simple P48 readings with new EM272 caps

 

Picking back up with the Primo capsules. I managed to lose one of the EM172 in a gap in the loft floor, so bought some EM272s.
Today I wired them up but there was a weird discrepancy of about 5dB between the two of them (They were both plugged into XLR ports on a MixPre6ii with pan L and R and both set to 50dB of gain). So I stopped and went back and checked everything was as it should be. The capsules were a matched pair, both resistors are reading 149.9K and they are wired as in the image below. As I've learned from the previous responses, the FET forms part of the circuit, so to ascertain that both capsules were getting the same voltage I probed them with the DMM, This is where it becomes more weird. Now I am seeing 0.19v on both no way near the expected 5V. Even accounting for the low voltage it doesn't explain how there is a 5dB difference between the two of them.
My question is two-fold;?
1. How using 4u7F Al caps correctly polarised, and 150k 1% resistors am I getting 0.19v across the +/- terminals on the capsules?
2. What could explain the 5dB difference between the two capsules? The capsules came from Micbooster, who I trust implicitly.

Apologies for my lack of knowledge...

On Mon, Mar 18, 2024, 15:29 kennjava <ken@...> wrote:
On Sun, Mar 17, 2024 at 11:20 AM, Adrian Hicks wrote:
So, am I correct in thinking that this is basically a resistor divider? With the FET being one of the resistances in the system?
Sort of, but that's an incomplete explanation.

Would I measure the resistance across the capsule in order to get the third value?
NO. The FET in the capsule is part of an active circuit; you can't just "measure the resistance" with an ohmmeter across the pins of a capsule.

?I've probably just opened a can of worms for myself by trying to optimise something that has worked for years, but I suppose it is all good learning.
It's both. The simpleP48 document is both a foolproof recipe, and a pretty good explanation of how it works.

To get more into it, you could read up on .

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