Post #14 is where "electret microphone" is revealed. But Arjune keeps wrongly calling it a "condenser microphone".
A condenser mic needs 48V applied between its diaphragm and back plate plus needs a preamp with a very high input resistance.
An electret mic has 48V permanently inside the electret material between the diaphragm and backplate plus it has a Jfet with a very high input resistance and the Jfet must be powered with a few volts at about 400uA.

For the L and R pins of the XLR connector to be balanced then both pins must have identical levels but inverts and both pins must have identical impedance to ground.

 

Once @Arjune gets the circuit built and starts testing it he will, as most would, pretty quickly what parts of the circuit need changes. No point in getting concerned that a concept may be a bit off. The proof is in the pudding.

 

to be clear
You believe that phantom power is applied to what pins on the XLR and what pin is the refetance to measure this voltage to ?

Phantom power supply is applied to pin 2 and the reference is pin 3 which is negative to pin 2. Then 1 is The shield of the cable which must be connected to ground. And only when The shield is grounded you can measure a voltage from pin 2 to pin 1.

 

Phantom power supply is applied to pin 2 and the reference is pin 3 which is negative to pin 2. Then 1 is The shield of the cable which must be connected to ground. And only when The shield is grounded you can measure a voltage from pin 2 to pin 1.

Nope.

The background,
once upon a time, "all" mixing desk inputs were through a transformer, and "all" microphones were a simple "coil", be that a real coil, or a transformer output,
With the microphone signal sent differentially on pins 2 and 3 of the XLR.

When phantom power came, the idea was simple,
the transformer on the mixing desk, had a centre tap added.
To this tap, a voltage of 48 ish volts was applied.
as this was the same on both sides of the microphone coil, no current flowed through the microphone coil.
The negative side of the 48 volts, was then connected to pin1. "signal ground" at the mixer.
At the microphone that wanted 48 v, a centre tap transformer was again used. Between this centre tap and the ground, there was 48 ish volts.

This is safe, if your microphone does not need the 48v, no current flows,

If there was 48v on pin 2, and zero volts on pin 3, that would put 48 volts across the microphone transformer / coil.
that is a quick way to blow a possibly expensive microphone,

If you really doubt what we say, and want the specification, I'd suggest go here

https://webstore.iec.ch/publication/30762#:~:text=IEC 61938:2018 gives guidance,is not a performance standard.

What your referring to could be a very very old "standard" called Tonader
https://www.soundonsound.com/glossary/tonader-power

we also used to call it "how to get a new microphone"

 

Hear are a couple of Circuits to refer to .............
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Hear are a couple of Circuits to refer to .............
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View attachment 277637
.View attachment 277638

The circuits are too complex for my understanding plus I'm suspicious about the 1K variable resistor at the ground terminal of the XLR Jack, I think it has to go directly to ground.

 

The circuits are too complex for my understanding plus I'm suspicious about the 1K variable resistor at the ground terminal of the XLR Jack, I think it has to go directly to ground.

What about the one without the resistors your worried about ?

Where do you stand now on the pins and which have phantom power on.

 

The circuits are too complex for my understanding plus I'm suspicious about the 1K variable resistor at the ground terminal of the XLR Jack, I think it has to go directly to ground.

I can see the reason for the ground-lift resistor - it's to get the bias right, but I can see plenty of reasons for having the case connected to earth.
Also, I wouldn't have considered MOSFETs for the job - nasty noisy things for low-level audio.

Could you please let us all know exactly what condensor microphone you are trying to amplifier - like a photo perhaps?

 

I can see the reason for the ground-lift resistor - it's to get the bias right, but I can see plenty of reasons for having the case connected to earth.
Also, I wouldn't have considered MOSFETs for the job - nasty noisy things for low-level audio.

Could you please let us all know exactly what condensor microphone you are trying to amplifier - like a photo perhaps?

but the one with the amps , does not use fets,

 

The Schematics that I provided are specifically for a special modification to certain
Electret-Condenser-Microphones,
which are constructed in a particular manner which makes possible the unusual connection.
The modifications were developed and outlined by Texas-Instruments.
The configurations shown allow High-Fidelity-Output at
extremely high Sound-Pressure-Levels,
all the way up to the point of mechanical-contact between internal-parts.
The reasoning for this is to facilitate very high level Audio-Spectrum-Sound-Analysis.

So, the Microphone-Connections and Biasing-Scheme
may not work with just any generic Electret-Microphone.

The Phantom-Power configuration shown is considered to be "standard" in the USA.
Other, lesser used, Phantom-Power-Schemes, do, or have, existed, utilizing different standards,
but all are based on an equal "Common-Mode-Offset-Voltage" using a Balanced-Line-Cable.
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What about the one without the resistors your worried about ?

Where do you stand now on the pins and which have phantom power on.

It seems that responding with a conscience is putting me in a bad situation.

 

I can see the reason for the ground-lift resistor - it's to get the bias right, but I can see plenty of reasons for having the case connected to earth.
Also, I wouldn't have considered MOSFETs for the job - nasty noisy things for low-level audio.

Could you please let us all know exactly what condensor microphone you are trying to amplifier - like a photo perhaps?

I don't have a condenser microphone that I can test because I cannot afford one and I have several dynamic microphones. A worker here at Green hills asked me to see what was wrong with his condenser microphone and that is basically the only experience I have with a condenser microphone that has to be powered externally. It was a Shure used for his church. He said he paid about $500 for it. It had a gooseneck. I wired up some voltage for phantom power with a 9 volt battery with a resistor and blocking capacitor and the microphone was working so I told him that maybe he has the power switch for phantom power shut off on his mixer. I told him to look for that switch on his mixer and then he said his microphone was working after he turned on the switch. I'm pretty sure I only used PIN 2 and 3 of the XLR plug for connections to test, that's what I remember. I recently bought a radio shack stereo electret condenser microphone that is used on eBay and powered by a 1.5 volt AA cell. The output was too low for my mixer so I added a button cell 1.5 volt battery in series with the AA battery at the positive terminal and the volume got about twice as loud. There was a funny thing about the microphone, it had hum when you held it so I added a spring contact from ground to the case and that solved the problem. The radio shack microphone is pictured.

 

What about the one without the resistors your worried about ?

Where do you stand now on the pins and which have phantom power on.

What about the one without the resistors your worried about ?

Where do you stand now on the pins and which have phantom power on.

I don't know exactly what you want to know about what resistors. I still have the belief about the pins on the XLR connector.

 

I don't know exactly what you want to know about what resistors. I still have the belief about the pins on the XLR connector.

I'm sorry , It could be one of the none standard power systems you are referring to , not the standard phantom power.
As such, the standard will not work for you .
Good luck on your experiments and I hope you don't blow up an expensive microphone.

 

. The radio shack microphone is pictured.

it looks like the sort they used to sell with their cassette tape recorders. What Connector does it have?
Which one are you trying to design a preamp for? Shure or Realistic?

 

it looks like the sort they used to sell with their cassette tape recorders. What Connector does it have?
Which one are you trying to design a preamp for? Shure or Realistic?

I'm designing a preamp for the shure like the one the guy gave me to test at Green hills. The realistic is already powered by battery and it has one quarter inch stereo plugs; L&R. Catalog 33-919a #.

 

In that case, the references I gave you in post #6 and those @drjohnsmith gave in post #10 are the correct ones to use. Phantom power is on pins 2 AND 3.

 

even if your phantom P,src requires very low current at normal/settled operation the 2N3904 might be a risky choice the 2N2222 , HSD965 , S8050 - would be perhaps a more safe choice . . . also the Schottky LC LP filter/half-wave_rectifier might perform better at HF