low noise transistor needed

Ricren · 11th November 2004, 02:25 PM

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 · 12th November 2004, 07:06 AM

BC550C

quasi · 12th November 2004, 09:31 AM

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 · 12th November 2004, 10:01 AM

BC550 , you are funny

Maybe SSM2220?
http://www.analog.com/UploadedFiles/...7SSM2220_b.pdf
Those are SO08 but I have DIL08 for sale

or MAT03

http://www.analog.com/UploadedFiles/...255MAT03_c.pdf

quasi · 12th November 2004, 10:25 AM

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 · 12th November 2004, 01:04 PM

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 · 14th November 2004, 06:19 AM

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 · 14th November 2004, 07:52 AM

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 · 14th November 2004, 09:10 AM

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 · 14th November 2004, 10:52 PM

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

11th November 2004, 02:25 PM	#1
Ricren diyAudio Member Join Date: Nov 2001 Location: Buenos Aires	low noise transistor needed 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

12th November 2004, 07:06 AM	#2
kilowattski diyAudio Member Join Date: Aug 2003 Location: Long Island, New York	BC550C __________________ ----------------------------------------------- Kilowattski

12th November 2004, 09:31 AM	#3
quasi diyAudio Member Join Date: Sep 2004 Location: Adelaide, Australia	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 __________________ http://sites.google.com/site/quasisdiyaudiosite/

12th November 2004, 10:01 AM	#4
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	BC550 , you are funny Maybe SSM2220? http://www.analog.com/UploadedFiles/...7SSM2220_b.pdf Those are SO08 but I have DIL08 for sale or MAT03 http://www.analog.com/UploadedFiles/...255MAT03_c.pdf __________________ /Per-Anders (my first name) or P-A as my friends call me

12th November 2004, 10:25 AM	#5
quasi diyAudio Member Join Date: Sep 2004 Location: Adelaide, Australia	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 __________________ http://sites.google.com/site/quasisdiyaudiosite/


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14th November 2004, 06:19 AM	#7
kilowattski diyAudio Member Join Date: Aug 2003 Location: Long Island, New York	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. __________________ ----------------------------------------------- Kilowattski

14th November 2004, 07:52 AM	#8
mandat diyAudio Member Join Date: Oct 2003 Location: Gliwice	There is another solution - THAT300 4xNPN, THAT320 4xPNP and THAT340 2xNPN. The main problem may be a low amplification coefficient. http://www.profusionplc.com

14th November 2004, 09:10 AM	#9
mandat diyAudio Member Join Date: Oct 2003 Location: Gliwice	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

14th November 2004, 10:52 PM	#10
Ricren diyAudio Member Join Date: Nov 2001 Location: Buenos Aires	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

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