# Low-noise audio-frequency BJT? [closed]

I found myself looking for a low-noise PNP transistor the other day.

I couldn't find any parametric searches that listed noise performance. Even from the transistor manufacturers. You can search by beta, $V_{ceo}$, and $I_{c}MAX$. All these searches seem to return a table of every general-purpose part in the manufacturer's portfolio. Not helpful.

This circuit needs to have low-noise at audio frequencies. RF transistors seems to be better characterized for noise, but they aren't necessarily low-noise at audio frequencies.

The best I have found was a forum thread at DIYaudio, but the recommendations tended to be old-school, even obsolete parts. I'm looking for a mass produced transistor in SOT-23 or smaller.

So recommendations are welcome, but I'd really like to see a selection tool or parametric search that includes this information.

I found BC859/BC860 with a search on the NXP web site. They seem similar to the BC108 which used to be the low-noise device most people used to use.

This is an old post, but the question is still relevant -- cheap, low noise, mass produced PNP SOT-23 transistors.

The Toshiba 2SA1312 is in SOT-23 with published noise specs, although I'm not impressed by NF charts. Digikey supplies them (in quantity).

The Fairchild FJX992 looks to be a similar part with no noise specs. Mouser has singles stock at $0.294 The BC859 looks a little old in comparison, but is in current supply at Mouser. MPS4355 if RS (source resistance) is low — up to a few hundred ohms 2N4250 is RS a few K ohms http://www.thatcorp.com/THAT_IC_Selection_Guide.shtml#XsistorArrays • Could you explain what 'RS' means please. Your links seems irrelevant as it doesn't contain any of the products mentioned. – Trygve Laugstøl Nov 22 '12 at 13:51 • @TrygveLaugstøl Source resistance driving the base of the transistor. If it's very high, current noise dominates and you need to use an FET instead of a BJT – endolith Jul 22 '15 at 20:49 Look at what the ham radio guys use for their direct conversion receivers . since the sensitivity of the direct conversion receiver depends on the low noise audio amplifiers that follow the RF mixer that conversts the signal direct to audio . you may find some good recipes there cheers mike ZL1BTB For audio purposes I often use the IF3602. Its over$40 each and has a huge lead time, but is the lowest voltage noise FET I've ever seen: < 1 nV/rHz at audio frequencies and has a large input impedance.

A good BJT PNP is the SSM2210. With a few of these in parallel you can get an input referred noise of ~0.5 nV/sqrt(Hz) from 0.1-10000 Hz.

• SSM2210 is obsolete – markrages Sep 2 '14 at 0:12
• True! Shows my age... – Ru887321 Sep 3 '14 at 5:05
• but the SSM2212/2220 seems to be a good replacement for NPN/PNP. Balanced pairs and still comes in 8-pin DIP. – Ru887321 Sep 5 '14 at 11:09