Where have all the Low Noise Transistors Gone?

I have been having a bit of a problem trying to locate low noise transistors....

The threads that were suggested when I started this one have been followed and yielded some info, but nothing that I can really use.

2SB737 was discontinued years ago.

2SA1085 seems to have been discontinued in the past year or so.

What is going on in the world of electronics?
Why are these useful parts being discontinued?

What parts are being used in low-noise applications?
Does anyone have any suggestions for low Rb transistors?
Through-hole and surface-mount devices are both acceptable.

Typical applications are RIAA preamps, microphone amplifiers and summing amplifiers.

Any help or suggestions will be appreciated.

Thanks,

Gareth.
 
Hi
I recently had the same problem finding low noise and low capacitance transistors. I tried to replace;
-2sa872 and 2sa1085 for the input stage
-bf422 and bf423 as general transistors
- 2sc2238 and 2sa968 for the driver stage
All now not available.

I chose the following as my relacements;
-ksc1845 andksa992 for the input
-ksa1381 and ksc3503 as general purpose
-2sa1837 and 2sc4793 for the driver stage
these seem to work fine for me

Don
 
The SMT 2SC3324 and 2SA1312 are available and look good on paper
I need to make fixture to test them out and compare.
I do not think a992 is as good as a1085 or b737.
Maybe some 2sa1083,a1084 are available, if you can use the low V version of them. But definitely not something that is RFND.
To bad for Gareth, as I assume his pcb's are laid out for TO-92, thus will need to do it again to fit a SOT-23 and have to convince the customers soldering sot-23 is not hard to do.
Rick
 
Thanks for the replies! The day has been spent looking for parts and suppliers, sometimes successfully, more often unsuccessfully. It does seem that we are a unique group of people with a unique need for low noise devices.

Rick,
At this point I have adequate and matching stocks of 2SB737 transistors and PCBs for various purposes. The search for new parts is for new designs and new PCBs. ;)
Giving thought to the potential reluctance to soldering SOT23 devices, one solution would be to supply boards with the SOTs pre-mounted - this is possibly not too smart as there is a risk of damaging the SOTs during general board handling. Another solution is to do a small subcard with pins and the SOT pre-mounted on the subcard. The subcard pins could conveniently be arranged to line-up with an in-line TO92 pin-out.

Cheers,

Gareth.
 
Hi Gareth and others,

It is good to hear that you have ample supply of b737. Maybe this is why Elektor & Doug Self chose a1085 and not b737 for the 2012 pre-amp, so they would not deplete your valuable stock? :)
Knowing, that this Rohm part b737 is long obs, wise to have stocked up as you must have done.
It all depends on the volumes involved, if it is sustainable and for how long.
Above even applies to new designs although designing with obs. parts is never a wise choice to make from my experience. I try to design using parts that are 2nd sourced, but we all know it can't be done 100% of the time.
one solution would be to supply boards with the SOTs pre-mounted - this is possibly not too smart as there is a risk of damaging the SOTs during general board handling. Another solution is to do a small subcard with pins and the SOT pre-mounted on the subcard. The subcard pins could conveniently be arranged to line-up with an in-line TO92 pin-out.
I believe it is gross over-kill and a unneeded expense, but you know better than I, based on the feedback from your customer base.
Personally, i'd rather chose to educate the masses of the ease & technique of smt esp., something such as a sot-23. If is a DFN then I agree 100%, to use a carrier for diy purposes.

P.S. Good idea to make the pots have alternative footprints for the new pre-amp2. I did this a few years back when I noticed that Alps and Panasonic offered similar footprint duals.
and nice chatting with you, keep up the good work.

Regards
Rick
 
I use 2SA(KSA)992FB for PNP and 2SC(KSC)1845FTA for NPN they are both high voltage, high gain and very low noise.
Currently available from Mouser.uk, RS Components, Farnell and CPC plus many more suppliers like Maplin etc.

these are the devices being used by most of the major audio manufacturers these days.... they are plentiful and inexpensive. just be aware that KEC/KIA occasionally has difficulty with the purity of their silicon, and there are batches of these devices that have high failure rates from time to time.
 
these are the devices being used by most of the major audio manufacturers these days.... they are plentiful and inexpensive. just be aware that KEC/KIA occasionally has difficulty with the purity of their silicon, and there are batches of these devices that have high failure rates from time to time.

it'd be nice to find somewhere that even sells the KEC transistors !
 
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I use 2SA(KSA)992FB for PNP and 2SC(KSC)1845FTA for NPN they are both high voltage, high gain and very low noise.
Currently available from Mouser.uk, RS Components, Farnell and CPC plus many more suppliers like Maplin etc.
I think the prefixes KSC/A may be recalled by some as Korean sourced. I'ts clear from Mouser and Digi-key catalogs at least, that this is actually Fairchild product and the various prefix codes they use, like KSC/A etc. just avoid EIJA part numbering /licencing issues with the OEM 2SC/A prefixes. 'Nothing new there.
 
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Theses are 0.8A devices and not low noise.
The low noise BC series are mainly BC414/416 and 550/560
wich are 45V VCE , other parts like BC109/179 , 214 , 239
and so on are lower voltage parts.

The base spreading resistance of BC550 is more than 100ohms, the Rbb from BC327 is in the 30ohms, the BC327 has lower noise than BC550.
Some transistors from zetex, also have very low base spreading resistence. But they do not indicate noise parameters or Rbb values in the datasheet, I think the main reason is that the Market for low noise bjt is nowadays very small, but there are some threads about Rbb measurements in the forum.
I have buy some biss transistors from NXP to test. But as I said before I have very good results with BC327/337, very low noise, high linearity, high hfe, and also high current capable, and of course very cheap :)
 
The base spreading resistance of BC550 is more than 100ohms, the Rbb from BC327 is in the 30ohms, the BC327 has lower noise than BC550.
Some transistors from zetex, also have very low base spreading resistence. But they do not indicate noise parameters or Rbb values in the datasheet, I think the main reason is that the Market for low noise bjt is nowadays very small, but there are some threads about Rbb measurements in the forum.
I have buy some biss transistors from NXP to test. But as I said before I have very good results with BC327/337, very low noise, high linearity, high hfe, and also high current capable, and of course very cheap :)

And they should really NOT be called 0.8A devices :)
Their optimum current are 10mA as the hfe falls above 10mA and the maximum FT are also not far from 10mA.

Using a transistor in the region with both falling hfe and FT are not recommended.

As the BC327/337 are manufactured by several companies the data sheets have a 1:3 or 3:1 deviation. FT are 100MHz or 260MHz depending on witch data sheet from witch manufacturer.

If someone could buy BC327-40/BC337-40 from 3 - 4 of the manufacturers and measure the specs including noise it would be great as it may be a very good transistor for audio :D
 
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