Mon Dec 6 02:47:38 EST 2010
Picking a staple transistor (BC549-BC559)
EDIT: Starting from futurlec transistor value pack and what I find
commented on http://www.diyaudio.com and http://www.diystompboxes.com
What I want: to pick a single NPN-PNP transistor pair that's cheap and
good enough for non-power audio apps. Needs high current gain (for
input impedance), low noise for small signals/preamps. Not so
important: bandwidth, max current/voltage/power.
Transistor selection is still a bit of a mistery to me. What I do
(think I) understand is this:
- Bandwidth, not so important for audio
- Noise, important for small signals
- Current gain, important for input impedance of emitter follower
- Max voltages, max power only really relevant for power amps.
What I don't get:
- Difference between switching, small signal, general purpose.
- @Ic, collector cutoff current? (probably only for switching)
- price: why is there such a huge difference (factor 50).
This is what's in the value pack which contains the most popular
10 BC327 PNP 500mA 100-600
10 BC547 NPN 100mA 110-800
10 BC548 NPN 100mA 110-800
5 BC549 NPN 100mA LN 200-800
10 BC338 NPN 500mA 100-600
10 BC337 NPN 500mA 100-600
5 BC107 NPN 100mA 110-450
10 2N2222 NPN SW
5 2N2907 PNP SW
5 C1815 NPN
5 C9013 NPN SS
5 C9012 PNP SS
My summary of on-line search is this: (PNP / NPN)
2N5087 / 2N5089 for low-noise, general purpose
BC560 / BC550 for low noise.
C9012 / C9013 for small signal
The latter are cheapest.
I need to look at the datasheets to check these out. It's probably
best to stick to one staple transistor and leave component
optimization for a later stage.
Sheets (internal refs)
These are pretty thin. Cheap, current gain: 64-250
C9012 PNP md5://2a5fbc943ff0fd700f9db3501ca54cb7
C9013 NPN md5://0dcb0103571f86d446f01d20b5589683
More current gain: 400-1200
2N5087 PNP md5://6bc41770417204ff4953c15ec2fee282
2N5089 NPN md5://41bab55c79bf466d87189edd8e920003
BC560 PNP md5://a4fb0b631e6d9a9016785126a73fce07
BC550 NPN md5://0a781a7c276c53cc2c1e77cac77f26ed
Looks like BC559 / BC549 would also be ok, but 30V instead of 50V.
They can probably take the place of anything I want to do so let's
drop the the C9012/13 and 2N5087/89.