BC547 to BC550: What to chose?

[Coriolis]

These BC prefix transistors are common and cheap over here en Euroland, and so I see them used a lot in different schems, especially synth stuff. Now, reading the datasheets, I see that BC547 takes higher voltages than BC 550, but that BC550 is low noise and still takes 30V of Vce, so could be used with bipolar 15V supplies, which is pretty much standard for synth apps and a lot of other audio gear. Other than that, I see no differences in the datasheets. So why not just use 550's (and pnp equivs 560's) for everything? Also I've seen schems of discrete opamps using 550's with +/-24V rails, so they should just about go anywhere (in audio)?

Or what?

C

[TheBigMan]

BC549C (NPN) and BC559 (PNP) are generally what I use as the standard parts where I can't get hold of the specified one.  E.g. 2N5088/5089 aren't easy to find in Europe so BC549 is what I usually use.  BC559 is the PNP complement so equivalent to a 2N5087.  If the 550 and 560 are pretty much the same then they'll do for just about any general purpose circuit using transistors.

[Coriolis]

Yeah, I had a feeling they might be pretty all round devices. I'm building mostly synth circuits right now, and I need to do a fair bit of matching of transistors for stuff like ladder filters, expo pairs, etc, and most of the circuits I want to build use BC54X for something. I get a feeling it's not critical in these designs whether BC547 or BC550, it's rather a question of matching, the right gain figure, and what the designer had in the parts drawer that day. I'd like to just buy a big batch of, say, BC550's and their pnp equivs 560's, so I can measure and match from these. 546 through 550 cost the same from my supplier, so it would great to just stock up on one type, if it really isn't critical...

C

[puretube]

the `47 & `48 are noisier than the `49 and the `50
same (`7 & `8) goals for the PNP equivalents (`59 & `60).

[Coriolis]

Yep, I know ! So why use anything else but 550/560's for small signal audio? Assuming you can get them? Just wondering...

C

[puretube]

for new designs I only use `50/`60 now...
(still got a few k old `49 & `59 in stock, though)

[Coriolis]

Well sir, that's good enough for me! I'm think I'm going to stock up on those then...

C