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Ian Finch 7th September 2010 07:22 PM

Complementary Questions
Hi folks
A FAQ about complementary transistors is: Are are they really complementary or just close enough for some tasks? Mullti-sourcing of small-signal types makes it difficult to compare datasheets since they can vary in data format and depth. I'm sure there are experienced professionals and amateurs who have a clearer understanding of what is fact and not in silicon matters.

The economical NPN series BC546,7,8,9,50 and PNP BC556,7,8.9, 60 have long been cited as complementary. eg BC546 + BC556 or BC549 +BC559.
Are they really? When Philips, Siemens and only a few other Europeans produced them they certainly were not considered so. One recommended audio complement for BC549 in a Wien oscillator circuit was actually 2N or PN4250!

Are the later BC550/560 indeed considered complementary? Reading ON Semi data sheets might lead you to agree, since some graphs appear to be just copies! Not all manufacturer specs are actually like that and I wish to stay with this series as it is...(ahem)..was..widely available.

Do you have any thoughts or an opinion on whether to trust these TO92 types as compllementary for use in audio preamps or buffers for example? :confused:

lineup 7th September 2010 11:38 PM

Those you mention from BC-series are as complementary as small signal transistors usually are.
Term COMPLEMENTARY does not mean they are same in HFE or VBE
but they are similar in many ways.
So, they are good to use together.

To make one NPN and one PNP with perfect match is close to impossible.
What I know it has never been done and I doubt it ever will be.

If you use BC546/556 or BC550/560 it is a fair match.
Gain, hFE and VBE, BE-voltage will be different.
How much different is from case to case.
Depends on the production.
Sometimes is a bit better match, other times less.

Ian Finch 8th September 2010 05:25 AM

Thanks for the reply, Linie. I consider it a compliment. I suspected that the newer types you show in bold type were considered better complements than some of the earlier types.

I plan to make a low power amp with basic mirror image input stage, like Rotel, Electrocompaniet and many others have done. Without CCS or Current Mirrors, I only guess that match may be a little more important.

east electronics 8th September 2010 10:01 AM

Ian's coment and post make absolute sense from many aspects

----now days we dont know any more what exactly we buy ....
got my shelf 200 pcs of BC549 made by philips all of them same batch but hfe varied from 180 to 450 ... makes no sense

got myshelf 100pcs BC557 from siemens ( ?? ) had no batch number onthem only the number 341 ....99% of them had hfe of 341 !!!!!!probably military specs that fell of in the market by accidednt

---- now days it seems that market is full with many diferent parts and especially small things need to be extensivelly tested before used in high quality applications

obviously even in the most simple audio application that uses a diferential LTP or any other similar tranistor application transitor matching is mantatory and will result to better performance

even in the most simple application the P3A using carefully matched transisitors increased tightness of the bass made it more punchy and the all amlifier behaved by far better ( of course in my version of the P3A the LTP stages features beyond matched LTP pair a thermal junction . )

a living example of the importance of complementary is the TITAN amplifier from the ELEKTOR circuits that anybody that builded found out that was a machine impossible to stabilize and make operate properly unless used tranistors that had the specific data and performance of the simulation and then againo those needed to be matched with the oposite pairs on the other side ...

regards sakis

( hello Ian !!!! how are you ??? any news ???)

Ian Finch 9th September 2010 10:43 AM

Hi Sakis
Those BC557 will take some time to use. I would think twice about that supplier next time. Still, you now know the tester is accurate, eh?

There are other parameters like Noise Figure, Ft, Cob etc. that are a problem. Just when you think you have a pair, some have PNP with 4 times the NPN figure or vice versa. Greg Erskine's recent transistor listing on his website seems like an impossible task when you think about High-end demands.

O/T..... Yes, apologies for slow progress, my friend. I will email.

CBS240 10th September 2010 06:05 AM

IMHO, if 'high end' is the goal, why not fork out a few extra bucks for some matched pairs, like THAT 3XX, MAT, or ALD matched mosfet devices?
Then you don't have to worry about it.:)

The THAT 3XX transistors have very good NF and Ft, Hfe is typically 80 - 100. But you don't need much current gain for a line input stage anyway. They make great mirrors, no degeneration required.;)

knutn 10th September 2010 09:47 AM

I don't know who said the following: "PNP and NPN transistors are as complementary as men and women".

It's true!! :)

lineup 10th September 2010 09:53 AM

That one was good, knutn

Ian Finch 10th September 2010 06:36 PM

If I remember correctly, Doug Self credited NAIM designer Julian Verekher with that phrase. It was used to explain his choice of quasi-complementary OP stages. Somehow, it seems to give a different meaning in that context. I won't go any further with that!

Hi CBS, thanks for the suggestion. I should not have referred to Hi-end really. Guys building it would probably not even consider BC series parts.

Greg Erskine 10th September 2010 08:16 PM


Originally Posted by knutn (
I don't know who said the following: "PNP and NPN transistors are as complementary as men and women".

It's true!! :)

Hi knutn,

Is that a reference to the different majority carriers, electrons and holes? ;)

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