Lowest noise BJT transistor?

Joshua_G · 29th October 2012, 09:34 PM

Which are the lowest noise BJT transistors, both NPN and PNP, which are in current production, regardless of price?

MarcelvdG · 29th October 2012, 10:41 PM

Hi Joshua,

Are you interested in voltage noise, current noise or both? If the source impedance is extremely low you would normally be interested in voltage noise, if it is not, you would normally be interested in both.

Best regards,
Marcel

Joshua_G · 29th October 2012, 11:13 PM

I'm interested in both, but especially in voltage noise.

MarcelvdG · 30th October 2012, 08:49 PM

My favourites are 2SC2545/2SC2546/2SC2547 and their PNP complements (2SA1085 or something, I don't remember the exact type number). SSM2210/SSM2220 (cheap version of MAT02 and its complement) are also pretty good. I don't know if any of them are still in production, or maybe in production with a different package and a different type number.

For extremely low voltage noise, the Philips/NXP BFW16A used to be a good choice because of its low base resistance, but it is out of production. You could try a more modern low-noise wideband transistor, such as the BFU760F (RB=3.32 ohm according to its Spice model). It will be difficult to keep it stable due to its high transition frequency.

sreten · 30th October 2012, 08:58 PM

Hi,

Again as in the other zener thread, for low numbers parallel devices.

rgds, sreten.

MiiB · 30th October 2012, 09:03 PM

Does the BFU760F have a complement...??

MarcelvdG · 30th October 2012, 11:07 PM

Quote:

Originally Posted by MiiB

Does the BFU760F have a complement...??

None that I know about.

teleman · 6th December 2012, 12:24 AM

2SA 872A (Hitachi)!.....this is the pnp version. Noise is specified between 2-5 dB maximum! I'm no expert, but perhaps someone else could through some light on this.

MarcelvdG · 10th December 2012, 07:08 PM

Quote:

Originally Posted by teleman

2SA 872A (Hitachi)!.....this is the pnp version. Noise is specified between 2-5 dB maximum! I'm no expert, but perhaps someone else could through some light on this.

According to the last graph in the datasheet, the optimal noise figure is 2 dB related to 190 ohm at 1 mA collector current, 1 kHz. The noise contribution of the transistor is then equivalent to (10^(2/10)-1)*190 ohm ~= 111.1297 ohm. About 13 ohm of this is collector shot noise translated back to the input (half of kT/(qIc)). As 1 mA is the optimum according to the graph, the contribution of base shot noise must be roughly the same. That leaves some 85 ohm for base resistance thermal noise.

85 ohm is not bad at all for a discrete low-frequency transistor, but not exceptionally good either.

gentlevoice · 04:25 PM

Hi Marcel,

Interesting thread ... would you happen to have advices on current production low-noise complementary BJT's? I searched for the 2SC2545 on Mouser's pages but it doesn't appear to be in their catalog ... In my context can be low voltage/current/high fT as well.

Best regards,

Jesper

P.S.: is it correctly understood that the BFU760F only accepts 2.8 VDC between collector and emitter?

29th October 2012, 09:34 PM	#1
Joshua_G diyAudio Member Join Date: Nov 2008 Location: Israel	Lowest noise BJT transistor? Which are the lowest noise BJT transistors, both NPN and PNP, which are in current production, regardless of price?

30th October 2012, 08:58 PM	#5
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, Again as in the other zener thread, for low numbers parallel devices. rgds, sreten. __________________ There is nothing so practical as a really good theory - Ludwig Boltzmann When your only tool is a hammer, every problem looks like a nail - Abraham Maslow

30th October 2012, 09:03 PM	#6
MiiB diyAudio Member Join Date: May 2005 Location: Denmark	Does the BFU760F have a complement...?? __________________ http://www.linkedin.com/pub/michael-...esen/a/a55/544 http://www.raidho.dk/

11th December 2012, 04:04 PM	#10
gentlevoice diyAudio Member Join Date: Oct 2007 Location: Aarhus, Denmark	Hi Marcel, Interesting thread ... would you happen to have advices on current production low-noise complementary BJT's? I searched for the 2SC2545 on Mouser's pages but it doesn't appear to be in their catalog ... In my context can be low voltage/current/high fT as well. Best regards, Jesper P.S.: is it correctly understood that the BFU760F only accepts 2.8 VDC between collector and emitter? __________________ ... Being mindful about sustainability also in my audio endeavors matters to me ... paying CO2 - and a quite fair pollution - compensation helps create a good listening "energy" ... Last edited by gentlevoice; 11th December 2012 at 04:25 PM.

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29th October 2012, 10:41 PM	#2
MarcelvdG diyAudio Member Join Date: Mar 2003 Location: Haarlem, the Netherlands	Hi Joshua, Are you interested in voltage noise, current noise or both? If the source impedance is extremely low you would normally be interested in voltage noise, if it is not, you would normally be interested in both. Best regards, Marcel

29th October 2012, 11:13 PM	#3
Joshua_G diyAudio Member Join Date: Nov 2008 Location: Israel	I'm interested in both, but especially in voltage noise.

30th October 2012, 08:49 PM	#4
MarcelvdG diyAudio Member Join Date: Mar 2003 Location: Haarlem, the Netherlands	My favourites are 2SC2545/2SC2546/2SC2547 and their PNP complements (2SA1085 or something, I don't remember the exact type number). SSM2210/SSM2220 (cheap version of MAT02 and its complement) are also pretty good. I don't know if any of them are still in production, or maybe in production with a different package and a different type number. For extremely low voltage noise, the Philips/NXP BFW16A used to be a good choice because of its low base resistance, but it is out of production. You could try a more modern low-noise wideband transistor, such as the BFU760F (RB=3.32 ohm according to its Spice model). It will be difficult to keep it stable due to its high transition frequency.

6th December 2012, 12:24 AM	#8
teleman diyAudio Member Join Date: Jul 2008	2SA 872A (Hitachi)!.....this is the pnp version. Noise is specified between 2-5 dB maximum! I'm no expert, but perhaps someone else could through some light on this.

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