Oktava MKE271 use with Phantom 48V any advice?

[ln76d]

Does anyone have an idea how to convert Oktava MKE271 electret microphone to use it with phantom 48V instead 3V battery?
I was thinking to use well known circuit of P48-T12 converter but with 3V zener diode instead 12V. 
I want to stay with original circuit, only change capacitors for new and KT361G for newer pnp type.

 

[ln76d]

Here's T-power converter schematic.

 

[ln76d]

Does something like this could work or this is totally stupid idea?

 

[ln76d]

Or like this?

 

[RuudNL]

I would do it like this:

 

[ln76d]

Really thanks for help

Does the 48v don't hit direct in T1 transformer?

 

[Gus]

I would do it like this:

I would figure out what the current needed is for the microphone preamp.  The use Ohms law to calculate the two resistors you added that look to be 2.2k each. 

I am assuming 2k21 is 2.21k?

6.8k phantoms and 2.2k are a 3.4k +1.1K = 4.5K load (48VDC-3VDC)/4.5K = 10ma

Quickly looking at the circuit
3K emitter resistor means under 1ma max current draw for that stage(3VDC/3K=1ma) and 10K in the first stage means under .3ma(3VDC/10k = .3ma) for that stage
so size the resistors for about 2ma, 1ma for the zener and 1ma for the circuit.
48VDC- 3VDC= 45VDC
45VDC/2ma = 22.5K
22.5k -3.4K = 19.1K
19.1k x2 =38.1K so two matched 39ks will be just under 2ma
I would also add a something maybe like 100 ohms after the zener and filter it again with a cap
So you might want a >3VDC zener or maybe even LED(s) or even a transistor zener/led circuit

Now to do this the most correct way calculate the resistors at the accepted range of phantom power you will find in the real world.  Do this for both min and max phantom voltages and select the resistors that will work.

This is some fast ohms law math you can fine tune the values or shunt regulator circuit to your liking.

 

[RuudNL]

I would also add a something maybe like 100 ohms after the zener and filter it again with a cap

Yes, that would be a good idea to reduce the zener noise.

 

[PRR]

> just under 2ma

It's easier than that.

Russian looks-like-"B" is Volts.

R5 has 3V-2.72V or 0.28V across it. Since R5 is 3K, we figure 0.28V/3K= 0.1mA.

Similar math around R2 gives 0.2mA. (Funny the 1st stage sucks more than the 2nd.)

So the total consumption is like 0.3mA.

> zener and filter it again with a cap
> reduce the zener noise.

_OR_..... eliminate Zener noise with.... a battery!

At 0.3mA, battery life should be years, even if left on.
___________________________________

I don't understand why you want to change the PNP. It isn't critical like the JFET. It is locked in NFB so it does what it is told to do. Silicon transistors were very mature when electret mike capsules became common. And working inside a mike is always risky.

 

[ln76d]

Hi guys

i'm really thankful for all, cause i've learned few new things  from your posts!

I would also add a something maybe like 100 ohms after the zener and filter it again with a cap
So you might want a >3VDC zener or maybe even LED(s) or even a transistor zener/led circuit

Do you mean low pass RC filter with 100R and for example 100uF electrolytic cap?

I did the simulation in multisim and with the RC filter voltage drops to 2,977V.
I will try to do that way first. I found an original schematic which shows 2,8V battery. Probably 2,8V-3V source should work well.
Best will be decrease amount of parts, because there's not many room inside the mike. Extra parts will be mounted without pcb.

I don't understand why you want to change the PNP. It isn't critical like the JFET. It is locked in NFB so it does what it is told to do. Silicon transistors were very mature when electret mike capsules became common. And working inside a mike is always risky.

My idea is put almost everywhere new parts. In original circuit i want to stay only with enclosure, capsule, trimmer pot, transformer and probably R1 resistor (which for now is mysterious part ) .
Why? For fun I want to check that it will improve sound (KT361G looks little bit crappy too )
I can always back to the KT361G.

Those are really good microphones, what i didn't expect, and i have four of them so i can play with them.
Probably i will not use them anyway,  but i want to do that from curiosity and to learn something new.
I could make new circuit like for example Scott's Helmke "Alice microphone", it would be easiest, but i think the better fun will be with the original circuit. 
For KT361G i found that the direct replacement should be 2N3905, but probably many of pnp should work here.
For KP303A, i found 2sk30A, j201 and probably BF245 will work too.
In both case still i need to look well into  the datasheets.
Mysterious R1 in two mikes is 68Mohm, then i have 82Mohm and 56Mohm.
On schematic is 560Mohm, so it's quite different value.