That looks like the schematic Flatpicker drew after we had a conversation it is a simplified KM84 like circuit. That works fine with Phantom.
Listen to what bockaudio posted the external power supply can matter.
The twisted pair cap was made of wire wrap wire I could not find a good small pf cap at my bench at the time. I built that circuit in two different bodies. I matched both jfets as close as possible so both circuits bias the same way and with a 3.9K source resistor. Why a 3.9K because that what was in the PDF "microphones" and I wondered why 3.9K was shown in the PDF. I noted an interesting thing with the IDSS and the ID the circuit runs at. One was built in a piece of fence pipe and the other in a MXR V67 body. The sound seems to follow the body my simple test was to exchange the capsules between the bodies.
One of my best builds is a external powered solid state microphone. I have a number more in sims some hybrid some all solid state. Some transformer and some transformerless
IMO you need to think about what makes a tube plate out to output transformer sound the way it does?
What makes a solid state transformer out sound like it does?
What makes a tube transformer out sound like it does?
What are the interactions?
How deep do you want to research this?
I stopped building testing sometime ago because the next steps would require expensive instrumentation and a good test chamber and a lot of time to do correctly. I even looked into vacuum chambers for coating diaphragms and winding machines for building my own transformers. IMO not worth it unless I had a microphone company and you need to think about liability.
With 48VDC phantom the current is limited by the 6.8k resistors this limits the current and power.
QUESTION has a phantom powered microphone ever started a fire?
If you use an external power without voltage and current limiting you need to think about available current/power at the microphone end and in the power supply if it fails you don't want a fire or shock hazard.
Listen to what bockaudio posted the external power supply can matter.
The twisted pair cap was made of wire wrap wire I could not find a good small pf cap at my bench at the time. I built that circuit in two different bodies. I matched both jfets as close as possible so both circuits bias the same way and with a 3.9K source resistor. Why a 3.9K because that what was in the PDF "microphones" and I wondered why 3.9K was shown in the PDF. I noted an interesting thing with the IDSS and the ID the circuit runs at. One was built in a piece of fence pipe and the other in a MXR V67 body. The sound seems to follow the body my simple test was to exchange the capsules between the bodies.
One of my best builds is a external powered solid state microphone. I have a number more in sims some hybrid some all solid state. Some transformer and some transformerless
IMO you need to think about what makes a tube plate out to output transformer sound the way it does?
What makes a solid state transformer out sound like it does?
What makes a tube transformer out sound like it does?
What are the interactions?
How deep do you want to research this?
I stopped building testing sometime ago because the next steps would require expensive instrumentation and a good test chamber and a lot of time to do correctly. I even looked into vacuum chambers for coating diaphragms and winding machines for building my own transformers. IMO not worth it unless I had a microphone company and you need to think about liability.
With 48VDC phantom the current is limited by the 6.8k resistors this limits the current and power.
QUESTION has a phantom powered microphone ever started a fire?
If you use an external power without voltage and current limiting you need to think about available current/power at the microphone end and in the power supply if it fails you don't want a fire or shock hazard.
