Condenser Microphone Pre-Amplifier 48V phamtom power supply

[electrovanga]

Hello,
I am designing a preamp. I will use Focusrite Scarlett audio interface.
I have two questions.
1. Can I connect 48V to out+ in the schematic?
2. How do professional microphone manufacturers provide 48V on their PCB?

[wasedadoc]

Have you done any research on how phantom powering works?

[electrovanga]

Hi,
Yes, I did but I couldn't be sure wheather I can get this 48 volt from pin nuber 2 or 3.

[themadhippy]

but I couldn't be sure wheather I can get this 48 volt from pin nuber 2 or 3.

phantom + is normally on both

[wasedadoc]

Hi,
Yes, I did but I couldn't be sure wheather I can get this 48 volt from pin nuber 2 or 3.

So you have not yet understood phantom. 

[electrovanga]

I think I watched all the videos possible and read so many articles on the websites. However, I couldn't understand or be sure. Maybe, it is because of my fundamentals.

[coppice]

Phantom power is not well defined. The impedance varies, and the voltage is sometimes 24V instead of 48V.

[wasedadoc]

Where is your preamp to be located? At the mic capsule or in the mixing desk etc? The former has phantom power fed to it. The latter feeds phsntom power out.

Phantoms typically employ a centre tapped audio transformer. Power runs equally in same direction through the two balanced audio wires and returns via the third wire.

How can you be designing a preamp without understanding these basics?

[boB]

This looks right but do not forget the XLR pin 1 for power return

[electrovanga]

Thanks for the all answers. I will try to answer all.

My preamp will be inside of the microphone. I am tryin' to learn. I want to do more hands-on projects to see the real life. I will first simulate and then print the PCB.


The phantom power comes from scarlett. It is P48.

I understand that if I take the 48V from XLR's 2.pin for FDOpamps' positive and 3.pin for FDO's negative, then that circuit will work. I hope I understand it right.
I will connect the earthing to XLR's 1.pin. This will be the RF caps. I will also put small ceramic caps between 1-2 and 1-3.

[wasedadoc]

I understand that if I take the 48V from XLR's 2.pin for FDOpamps' positive and 3.pin for FDO's negative, then that circuit will work. I hope I understand it right.
I will connect the earthing to XLR's 1.pin.

Wrong.
https://www.prosoundweb.com/a-primer-on-phantom-power-for-condenser-microphones/
https://www.dpamicrophones.com/mic-university/know-the-basics-about-phantom-power

And you should be taking +ve equally from two wires.

[electrovanga]

Hello Mr. Waseda,
When you said wrong, I am confused a little bit. Therefore, I roughly draw what I wanted to say. Is this still wrong?

[wasedadoc]

Although that drawing is not what you previously said in words it is also wrong.  Two points.

1. You cannot have the +ve supply for the preamp directly connected to one of the balanced audio outputs.

2.  As drawn, the microphone capsule has no power. (They are at the same or almost same voltage.)

[electrovanga]

I might not explained well before. If I can't get it from the outputs, that means I need an additional power supply to give the 48V power. Then what is the advantage of phantom power. The phantom poewr gives 48V to the output of my FDO and my signal swings on the output. If I use this 48V and give it to my circuit's 48V supply which I shared at the first post, it seems that it will be OK. Power supply in Scarlett is constant voltage source right? Then I will always have 48V at the output and then I will not have dramatic voltage drops. That means my signal will swing  around the same range.

[wasedadoc]

No additional supply is necessary if you understand how it can work and do it properly. That is where you are failing.

On the internet you can find schematics of many commercial implementations. Study those until you understand the basics of how they extract power.

[wasedadoc]

Also, do you really mean a condenser microphone capsule (containing no electronics), an electret capsule (containing no electronics), an electret with integral FET or what?

[TimFox]

The original method for "phantom power" used transformer coupling for the balanced AC signal.
The DC voltage was applied to the center-tap of the "receiving" transformer with respect to shield ground.
A similar center-tapped transformer in the "transmitting" end then received the DC power from the center tap to ground.
Modern phantom power uses resistors to obtain a similar result without transformers.

[electrovanga]

Hello everyone,
I mean condenser microphone capsule(containing no electronics).

I made a little bit more reseach and I saw that I need to filter and regulate phantom power and then step it up again as dc signal. I think the reason why I can't use the +48V directly is when the sound signal sits on the phantom power it will be a noisy power supply. I will use hex schmitt inverter to make a charge pump. I think it will work this time.

[wasedadoc]

A condenser mic capsule is electrically a very low value capacitor. Tens of pF. (Yes picofarads.)

https://repforums.prosoundweb.com/index.php?topic=11961.0

You need very high input impedance amplifier and very high value resistor feeding the bias voltage into the capsule.  Hundreds of Megohms. Your proposed design is totally inadequate.

[wasedadoc]

You may not need to go to the measures you mention for the phantom powering but you do need sufficient isolation between the amplifier outputs and the signal wires which have the 48 volts on them. You cannot expect an amplifier to work properly if its output is tied to its power rail!

[electrovanga]

Hello Mr. Waseda,

I will try to get deeper into those feedbacks. Let me come with another circuit design to the discussion here.
Thanks for your support.

[Roehrenonkel]

Hi electrovanga,
 
please read:
https://www.ingwu.de/mikrofontechnik/mikrofonaufsaetze/26-12-elektrische-betriebstechnik-von-kondensatormikrofonen.html
https://www.ingwu.de/mikrofontechnik/mikrofonaufsaetze/27-13-die-48v-phantomspeisung-und-ihre-geister.html
....and then goto:
https://www.mikrocontroller.net/topic/220373

Good luck