Primo EM273 with P48 phantom power supply

[MicUlli]

Hello All,

I want to contribute another fine solution for the Primo EM273 3pin electret omni capsule. With only 10 components attached you will get a nearly professional solution:

Frequency response: 20..20000 Hz (-1..+3,5 dB)
Sensitivity: 15,6 mV/Pa (-36 dBV)
Equivalent noise: 16 dBA
Max. SPL for 1% THD: 133 dB

Find attached: frequency response 0° incident, electronic circuit, picture of the mic. body

Have fun

 

[k brown]

Curious - why bias the capsule with 22k @ 5v, when Primo spec sheet shows 5.6k for 5v?

Does input impedance of transistor lower it to more like 5.6k?

 

[rogs]

You might like to consider making the diode a zener? ... At present i seems that C1 charges via the capsule drain when first powered.
That may well put a voltage in excess of 10v temporarily across the capsule FET, which may well destroy it.

 

[analogguru]

So has this board now degenerated to a competition field with the title:
"How to destroy the FET of a capsule with the smallest amount of external components ?"

I think such a competition has already be won - I only have to prepare the tech side of it. So stay tuned.

So much can already be said:

- even fewer components than the circuit above
- probably due to fewer components, better specifications

Here are the claimed specifications:

- Directivity: heart shaped
- Sensitivity: 11mV/Pa @ 1kHz
- Frequency response: 40Hz - 20 kHz
- Output Impedance: 25 Ohm
- Noise Level: 7dB (A)(IEC651)
- Sound Pressure Level: 146 dB (SPL)
- Power Supply: 48V

 

[MicUlli]

@analogguru
Why do you think the capsule FET will be destroyed? I am courios to see the "tech side" you mentioned

 

[MicUlli]

@k brown
Due to the Vbe cpamp through the pnp transistor the internal FET of the capsule is driven into the ohmic region. This means smaller drain current compared to the pinchoff region. Therefore 5K6 is not sufficient.

 

[k brown]

What opamp? No opamp in the schem.

 

[MicUlli]

Due to the Vbe clamp through the pnp transistor...
Sorry for the typo

 

[k brown]

Would the more readily-avallable 1N4148 diode also work?

 

[MicUlli]

Yes, 1N4148 is working. The purpose is to catch negative voltage in case of signal line shortage.

 

[analogguru]

@analogguru
Why do you think the capsule FET will be destroyed? I am courios to see the "tech side" you mentioned

I am not talking about your suggestion. This should be clear because it has too much components - there is already another winner for the "smallest amount of components". In short time I will lift the secret, how this is achieved.

Here is the winner of this competition with "the smallest amount of components" including the claimed specs:

 

[mhelin]

Encore has the FET in preamp (not in capsule) which I guess is pretty much similar than used in all Violet and JZ mics (got to trace my Black Knight some day).

 

[k brown]

Yes, 1N4148 is working. The purpose is to catch negative voltage in case of signal line shortage.

Great, thanks.

 

[analogguru]

Encore has the FET in preamp (not in capsule) which I guess is pretty much similar than used in all Violet and JZ mics (got to trace my Black Knight some day).

Is your claim based on hearsay (like from sales lies/pictures), on dreams, or on experience because you bought one or more like I did ?

If it is the third case you are one of the few lucky ones and I would appreciate to see pictures of the innards of the one(s) you got.

In an exchange I will show now the innards of the two I've got (in two seperate buys).

As you will know, the most important part of a microphone is..... the capsule.

In this case it is an omni-directional 9,7mm el-cheapo capsule marked with "SG".



This is very important because inside this very special capsule is the very-high-sought-after FET 2SK596S-B. This FET is specified with an absolute maximum drain-source-voltage of 20V and an Idss of 150-240 µA.

The next important part is a ring of foam and a red and a black wire which are soldered to the capsule in this way:




You may ask "How can this microphone be cardiod when there are no holes at the back of the capsule ?"

The answer will come together with the answer to the question how a 9,7mm capsule can become a 14mm capsule - as it is claimed in the ad:




Nobody has lifted the secret yet for the two questions above, but I assume that the secret lies in the foam ring.



If there are some special chemicals in this ring - like for growing flowers - then the capsule will start growing and with time it will reach the final diameter of 14mm. By growing, the sturdy backside of the capsule first will get cracks which later will become holes and voila, the capsule has transformed from omni to cardoid.

Now you may ask: "...and the rest of the electronics ?"

Oh, the anwer is an easy one:
Just wire the black wire to pin 1 of an XLR-jack, and the red one to pin 2 (pin 3 stays unconnected) and you've got it: The microphone for 48V-phantom-power with the smallest amount of components and incredible specs everybody dreams of.

Now you need only some patience to determine how long the FET in the capsule will last when connected to ~ 46V DC (48V - 1,6V [across one 6k8 resistor]):

 

[MicUlli]

Haha,
now it is clear why the encore 300 disappeared in the dark, not available any more (at least in germany).

 

[mhelin]

That must be some fake Encore from Aliexpress. Is the pin 3 floating, doesn't work well with tx-input mic pres.

 

[mhelin]

... or from Wish:
https://www.wish.com/search/condenser microphone/product/60a83b9bc33f10885427c54f

 

[analogguru]

They will not work well on transformerless inputs either.... at least not for a long time with 48V phantom-power.....

No, they were bought on evilbay, more than a year ago.... I mean the case is ok so far and worth the little money I paid for them...

And yes, the cheap 25mm electrets will fit inside, also the cheap small assembled pcb's one can buy in china - modifications recommended:




Alltogether less than € 30,-- (including shipping), so at the end not a bad deal IMHO.

 

[jean-luc brion]

Bonjour
sur la photo du début la capsule est légèrement en retrait, je suppose que c'est intentionnel,
cela a-t-il à voir avec le pic de 3 db à 8000 Hz ?

 

[MicUlli]

Bonjour
sur la photo du début la capsule est légèrement en retrait, je suppose que c'est intentionnel,
cela a-t-il à voir avec le pic de 3 db à 8000 Hz ?

Yes, a little bit. The intention of the 2,5mm let in flush was to rise the sensitivity at 20 kHz. The let in flush has a broadband behaviour, therefore lower frequencies (8 kHz or so) are affected too.