low noise transistor needed

[Ricren]

Hi folks,

I'm looking for the lowest noise PNP small signal transistor for a microphone circuit wiith a 50 V power supply. I've been searching and a candidate would be the 2N5087, but I wonder if there's something better.
Could anybody suggest a better unit?

Thanks a lot.

Ric

 

[kilowattski]

BC550C

 

[quasi]

kilowattski !!!????

It's ok .... kilowattski meant a BC560C the PNP version of the BC550C.

If there is 50v across this transistor then the BC560 may not do.

Whew ...hope I got here in time.

Cheers

 

[peranders]

BC550 , you are funny

Maybe SSM2220?
http://www.analog.com/UploadedFiles/Data_Sheets/196449167SSM2220_b.pdf
Those are SO08 but I have DIL08 for sale

or MAT03

http://www.analog.com/UploadedFiles/Data_Sheets/23265255MAT03_c.pdf

 

[quasi]

What voltage sits across the transistor in question? Is it 50v or something else? If you don't know and have a cct we can work it out.

Cheers

 

[Ricren]

Circuit

Folks,
Thanks a lot for the suggestions.
I'm attaching the schematic of the "electret mic to balanced phantom power adapter " that I need to build.
Pins labeled XLR 2 and XLR 3 goes to the typical balanced input circuit of a regular mixing board. In that circuit you have 48 V DC applied thru a couple of 6.8K resistors.

So I think the voltage across the transistor (Vce) is way less than 48v. Anyway is nice to have voltage headroom, right?


Ric

 

[kilowattski]

Quasi,

Unfortunately for me the 5 and 6 on the keyboard are next to each other. Thank you for catching that, but it looks like Per-Anders has won the prize for finding the lowest noise transistor I have ever seen.

 

[mandat]

There is another solution - THAT300 4xNPN, THAT320 4xPNP and THAT340 2xNPN. The main problem may be a low amplification coefficient.
http://www.profusionplc.com

 

[mandat]

Can you change your mind? What do you think about specialised opamp like INA103 or INA163?
Look at Tomasz Brodniewicz's homepage
http://www.proaudio.nwz.pl/konstr_ina103.htm
You can find gif with manufacturer's application
http://www.proaudio.nwz.pl/pre_ina103.gif
author's application
http://www.proaudio.nwz.pl/ina103nowe.gif
PCB
http://www.proaudio.nwz.pl/inaboard.gif
and the last two in EAGLE format.
Application and PCB were done for dynamic micro.
Another link
http://www.mindspring.com/~benbradley/pre.html

 

[Ricren]

the circuit is great, belive me.

Mandat: Thanks for the sugestion. I actually use those ICs and they sound very nice.

But in this case, this circuit posted fits really well for the job. Is a version of a very clever circuit that Schoeps uses in their multi thousend dollars mics. Is minimalistic and does the job. In combination with a preamplifier with clean phantom power, it rocks.

The key is to use low noise transistors. I built it with BC558 and is a non go.

I'll chech the dual one that peranders suggested.

Tks again.

Ric

 

[jackinnj]

Hi folks,

I'm looking for the lowest noise PNP small signal transistor for a microphone circuit wiith a 50 V power supply. I've been searching and a candidate would be the 2N5087, but I wonder if there's something better.
Could anybody suggest a better unit?

Thanks a lot.

Ric

put 2 transistors in parallel and the noise will be something like:

NOISEnew= NOISEinitial *(1/SQRT2)

 

[Ricren]

Bummer

Ahhhh...the duals suggested by Peranders aparently will not work, because the Vce max is only 36 V.

So I think my only solution to date is experiment with the BC560 and try the paralell configuration suggested above.

I'll try.

Ric

 

[peranders]

You can use a cascode together with BC550/560

 

[Ricren]

Good idea (electronicwise) but I can not keep adding parts.. This circuit mus fit in an XLR connector.

But I'll try it anyway

Ric

 

[jackinnj]

Good idea (electronicwise) but I can not keep adding parts.. This circuit mus fit in an XLR connector.

But I'll try it anyway

Ric

time for SOT-23, and check out Intersil's surface mount transistor array's -- really nice devices in SO8

 

[jackinnj]

here's one which looks like it would fit in an XLR shell -- the author is well-published.

http://users.rcn.com/rhcamp/mm2v1p1.pdf