Low Noise Small Signal Transistors

dlucy

dlucy67 (Doug)
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I've noticed a few posts where AK'ers were talking about using a BC550 in place of a KSC1845 when they were replacing original small signal transistors in spots where low noise was critical. It got me rethinking my "always use a KSC1845F" and I spent some time researching "what all the small signal, modern production, low noise transistors for audio frequency amplification". I ended up with more results than I expected.

Any of these not low noise AF amplifiers? Or any of these that should not be in this list? This is meant to be a starting point when looking for a low noise amp transistor, not a always-works replacement list. If I've missed a low noise device that is currently made and sold, please let me know.

Device Polarity Comp Vcbo Vceo Vebo Ic Pc NF Package Pinout hfe qty price Link

PN5133 NPN - 20 V 18 V 3 V 1 mA - - TO-92 EBC 60-1000 $0.62 https://www.mouser.com/ds/2/68/lssgp077-26985.pdf
SS9014 NPN SS9015 50 V 45 V 5 V 100 mA 450 mW 0.9 dB TO-92 EBC 60-150,200-600,400-1000 $0.06 https://www.mouser.com/ds/2/308/SS9014-1121741.pdf
BC549 NPN BC559 30 V 30 V 5 V 100 mA 500 mW 1.4 dB TO-92 CBE 110-220,200-450,420-800 $0.06 http://www.mouser.com/ds/2/149/BC550-888526.pdf
BC550 NPN BC560 50 V 45 V 6 V 100 mA 500 mW 1.4 dB TO-92 CBE 110-220,200-450,420-800 $0.06 http://www.mouser.com/ds/2/149/BC550-888526.pdf
2N5089 NPN - 25 V 30 V 4.5 V 100 mA 625 mW 2.0 dB TO-92 EBC 400-1200 $0.22 https://www.mouser.com/ds/2/68/2n5088_20series-1130989.pdf
KSC1845 NPN KSA992 120 V 120 V 5 V 50 mA 500 mW 25 mV TO-92 ECB 300-600 $0.06 https://www.mouser.com/ds/2/308/KSC1845-1295526.pdf
PN2484 NPN - 60 V 60 V 6 V 50 mA 625 mW 3.0 dB TO-92 EBC 30-900 $0.22 https://www.mouser.com/ds/2/68/pn2484-771451.pdf
2N5088 NPN - 30 V 35 V 4.5 V 100 mA 625 mW 3.0 dB TO-92 EBC 350-1400 $0.06 https://www.mouser.com/ds/2/308/2N5088-1118431.pdf
2N3707 NPN 2N4508 30 V 30 V 6 V 200 mA 625 mW 5.0 dB TO-92 ECB 100-550 $0.69 https://www.mouser.com/ds/2/68/2n3707-3711-15606.pdf


SS9015 PNP SS9014 50 V 45 V 5 V 100 mA 450 mW 0.7 dB TO-92 EBC 60-600 - http://eng.bu.ac.th/datasheet/transistor/SS9015.pdf
2N3799A PNP - 90 V 90 V 5 V 50 mA 360 mW 1.0 dB TO-18 EBC 300-900 $2.17 https://www.mouser.com/ds/2/68/2n3798-254342.pdf
BC559 PNP BC549 30 V 30 V 5 V 100 mA 500 mW 1.2 dB TO-92 CBE 200-450,420-800 $0.06 https://www.mouser.com/ds/2/308/BC560-1118766.pdf
BC560 PNP BC550 50 V 45 V 5 V 100 mA 500 mW 1.2 dB TO-92 CBE - - https://www.mouser.com/ds/2/308/BC560-1118766.pdf
2N3964 PNP - 45 V 45 V 6 V 1 mA - 2.0 dB TO-18 - 250-600 $2.47 https://www.centralsemi.com/get_document.php?cmp=1&mergetype=pd&mergepath=pd&pdf_id=LSSGP057.PDF
2N3799 PNP - 60 V 60 V 5 V 50 mA 360 mW 2.0 dB TO-18 EBC 75-900 $2.17 https://www.mouser.com/ds/2/68/2n3798-254342.pdf
PN4250A PNP - 60 V 60 V 5 V 500 mA 625 mW 2.0 dB TO-92 EBC 250-800 $0.21 https://www.mouser.com/ds/2/68/pn4250a-555534.pdf
KSA992 PNP KSC1845 120 V 120 V 5 V 50 mA 500 mW 25 mV TO-92 ECB 300-600 $0.06 https://www.fairchildsemi.com/datasheets/KS/KSA992.pdf
2N4058 PNP 2N3707 30 V 30 V 6 V 200 mA 625 mW 5.0 dB TO-92 ECB 100-550 $0.43 https://www.mouser.com/ds/2/68/2n4058-4062-740844.pdf
 
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FWIW, I had read allusions to, somewhere on this, that B-stuff should not be used in japanese audio. I have no idea what that means aside from BC/BD series, or why the prohibition...
 
That is probably because European type number transistors lag half a day behind, compared to Japanese ones. ;).

Now, the fact probably is there are not much European types for higher voltages made especially for audio industry.


Some of the low noise were BC413 to BC416 made by Telefunken, but browsing I only see other manufacturers knockoffs of these obsoletes at the moment.
 
FWIW, I had read allusions to, somewhere on this, that B-stuff should not be used in japanese audio. I have no idea what that means aside from BC/BD series, or why the prohibition...

If you come across those mentions again, please post here.
 
:lurk: Timely thread, as I'm building a parts list for the Adcom GFA-1, and I plan to replace the 2SA789's and 2SC1583's.
KSC1845's and KSA992's were what I was thinking about, but since I know little about this hoping to learn something!
 
:lurk: Timely thread, as I'm building a parts list for the Adcom GFA-1, and I plan to replace the 2SA789's and 2SC1583's.
KSC1845's and KSA992's were what I was thinking about, but since I know little about this hoping to learn something!
Collector current for the 1845/992 is only 50 mA and it's 100 mA for the 789/1583.
 
Collector current for the 1845/992 is only 50 mA and it's 100 mA for the 789/1583.

Spot on! That is the exact reason I put together this list. There are places where the KSC1845 seems like a good choice, but its Ic is too low... so I needed a go-to list of truly low noise small signal transistors that I could reference in these situations.
 
Thanks! - So BC550/BC560 would seem to be better - right?
I see some have lower noise numbers than those though. Is there a good way for a beginner to choose between them?
Aside from just asking for advice here;)
 
Asking questions here helps you get answers... and the rest of us get to learn, too. So, please ask questions.
 
Starting off with your first transistor-to-be-replaced the 2SA789. What I could find on the net for specs were these:

2SA789
  • Polarity PNP
  • Material Silicon
  • Package X19
  • Vcbo 25V
  • Vceo 20V
  • Ved MAX 5V
  • Ic 30mA
  • Pd 150mW
  • fT 100MHz
  • hFE 150 typical
  • hFE bias 10mA
  • Pinout BCE
These are different than what @fernarias was quoting, so you'll need to double-check my specs. The process will be the same, though:


Narrow the above list in post #1 to just the PNP devices, then start weeding them out by each spec:

PNP: SS9015, 2N3799A, BC559, BC560, 2N3964, 2N3799, PN4250A, KSA992, 2N4058

All of them have a Vcbo equal to or higher than the 25V of the 2SA789, so the list stays the same.

All of them have a Vceo equal to or higher than the 20V of the 2SA789, so the list stays the same.

All of them have a Vebo equal to or higher than the 5V of the 2SA789, so the list stays the same.

The 2N3964 as only 1 mA of Ic, but the rest exceed the Ic of 30 mA on the 2SA789, so the potential candidates list drops to just:

SS9015, 2N3799A, BC559, BC560, 2N3799, PN4250A, KSA992, 2N4058

All of those exceed the Pd dissipation needs of 150 mW, so the list stays the same.

The specs I found say you want a hfe somewhere in the 150 range, but I'd check with a cheap component tester to see what you're getting right now from the installed devices. Regardless, you can use that range to narrow the list a bit more.

You may end up having to buy a sizable number of transistors if they are sold with a overly-broad range. That's OK when they are priced at $0.06 each in qty of 100.

Then look at the pinouts. You can always twist the legs around and insulate them against touching with short lengths of sleeve or heat sink.

If my specs are right and match your devices, I'd say you're looking at either the KSA992 or the 2N4058. But that's only if my 2SA789 specs are right. If @fernarias 100 mA spec for Ic is right, then the KSA992 isn't strong enough.
 
When I look up 2SC1583, all I get is a dual transistor. Is that right?
 
There are some Zetex devices that are very low noise such as ZTX1051A. It is a Vce 40V part, for a power amp it will need a cascode.
 
Yes - both of these are dual transistors. The 798 is on the 10 most wanted list though, and I know that this amp has had a lot of damage in the past.
More info on the unit in the Adcom GFA-1 thread here in Solid State.

Reading threads on these dual transistors here, and the Tuning Fork articles is educating me somewhat. I know that combining two units of matched hfe is the best bet for replacement.

As to the Zetex, I'm not smart enough to know what a "cascode" is.:crazy: That one I'll have to search.
 
There are some Zetex devices that are very low noise such as ZTX1051A. It is a Vce 40V part, for a power amp it will need a cascode.
That is an interesting part.

I refurbished an old Pioneer SA900 amp, it has a 2SC871 single transistor in the moving coil preamp. It was audibly noisy. I just wanted to put in another transistor.
Without any more knowledge I just "guessed" and put in a KSC2690, thinking about some J.L.Hood simple preamp I copied in my youth where a medium power transistor was used (just found it on google when I searched Paul Kemble Hood preamp).
Anyway, the noise was gone but having no TT at the moment I did not rally test it.

This MC amp is a single transistor common base design,
I wonder, would such Zetex transistor be a good choice there? The transistor has 2.6 Volts over C to E and a 1k emitter resistor (where the input connects) so it consumes some 2.6 milliamps. So it is low resistances everywhere.
Unfortunately, apart from reading articles, I am not good at math so I always have to guess about what to use, the noise theories a way above my understanding....
I would like to see your comment!
 
certainly would not hurt to try the ZTX1051A. using a KSC2690 is another option. You can make a little fixture and mesaure/test them out.
In the old days, folks used the low rbb' types such as Rohm, 2sd786/b737
Yes something to look u,p a cascode circuit configuration, should be lots of info about it.. It is used in a few amp designs to enhance performance.
 
OK thanks, I think about it and dig some internet info, no hobbying recently due temporary having only one eye avail and the other one on surgery, easier to chat on AK than soldering and refurbishing my pile of vintage stuff !
 
I wonder why the big legit sellers like RS and Mouser do not have that one. I am pretty sure Reichelt has no quality control. Will their buyers dept be alert on fakes? At least, they are not alert on quality of drilling stuff of the "Donau" brand which is that unusable it is a joke.
 
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