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I'm working with phototransistors, using them to capture audio rate fluctuations in light levels. I'd like to move from my current setup which uses a 9V battery for nice clean power to one that uses phantom power.

My working 9V circuit looks like this:

enter image description here

It works OK - pretty clean, good signal. My model for a phantom powered version would be something like this:

enter image description here

Does this seem like a workable direction?

It appears to have a higher noise floor than the battery version. I've been using a 220pf cap for C2, but I'm not convinced that's a good value. I'm trying to figure out if I can get away with this simple a network, or whether additional components are needed.

JRE
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mo-seph
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    Whether it works or not totally depends on the signal extraction and power-feed circuit at the other end of the cable. I suggest you simulate your circuit. – Andy aka Apr 10 '23 at 17:08
  • This is (hoped) to work with standard audio phantom power setups - it supplies 48v on the hot/cold pins, through a 6.8k resistor on each. It's hard to know what's at the other end - each manufacturer might implement it differently. – mo-seph Apr 11 '23 at 08:21

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In the end, I've found this to work fairly well: enter image description here

I've been playing with different values of R4 and R5 to set the gain - for what I'm doing, this network works OK.

mo-seph
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