# BC550C



## burger-patty-and-bacon (Sep 4, 2021)

Anyone have an extra BC550C or know where to source one without crazy shipping or quantity?   Or can I sub it with something?   Doing the ISOCELES bom now


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## benny_profane (Sep 4, 2021)

https://forum.pedalpcb.com/threads/transistor-question.907/post-5637


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## burger-patty-and-bacon (Sep 4, 2021)

"BC550C are low-noise, high gain NPN silicon transistors in a TO-92 package. 2N5088, 2N5089 & 2N5210 are all good replacements. The BC550C is rated for 45V, 2N5210 is rated for 50V, the others are rated for 35V. Should make no difference in 99% of the pedals we would build. One other thing to keep in mind when substituting transistors: sometime the pinouts are different. Such is the case here. The pinout for 2N5088, 2N5089, 2N5210 and most other TO-92 transistors is shown below. The BC550 has C & E swapped. If you sub a 2N transistor for the BC550, you have to put it in "backwards."



So I can source and use any of these instead as long as I put them in backwards:  2N5088, 2N5089 & 2N5210

Which one is the highest gain of those 3 - how would I determine that?


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## benny_profane (Sep 5, 2021)

All of the information you need is provided in the parts’ data sheets. The relevant information is the pinout and the DC current gain (hFE). This is given as a range (min, max, and typical) given certain operating conditions. The only way you’d know what the individual part’s hFE is to measure the actual device.

Note that you don’t necessarily want the highest gain part—circuits are typically designed such that they will function with the parts as characterized. You may need to alter other parts of the circuit if you change an active component.

That circuit uses a charge pump circuit to increase the input voltage (9V) to about 32V. (_Someone confirm that, please._) You’ll want to ensure that whichever device you use is rated accordingly.


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## caiofilipini (Sep 5, 2021)

burger-patty-and-bacon said:


> Which one is the highest gain of those 3 - how would I determine that?



As Benny said, the datasheet will give you a pretty good idea. Of those three, it looks like 2N5089 would give you the highest gain.


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## burger-patty-and-bacon (Sep 5, 2021)

Alright.. I will go with a 2N5089 vs. the BC550C.  Seems the BC550C is an older one and is no longer made and harder to find.  I will socket the thing so I can mess around with others.  This ISOCELES is proving hard to find a few parts for.  I ordered 5 new PCB's and am making a motherlode shopping list for all of the components!


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## fig (Sep 5, 2021)

I would suggest you socket the transistor and if it is not to your liking you can audition others.
I can send you a few options to try if you'd like.


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## burger-patty-and-bacon (Sep 5, 2021)

fig said:


> I would suggest you socket the transistor and if it is not to your liking you can audition others.
> I can send you a few options to try if you'd like.


Hehe. Yes, sir.  I edited my post after posting to add that I would be socketing.  I am nerding out on some specs and see on DIGI KEY some very easy to read "GAIN" info.

BC550C says

DC Current Gain (hFE) (Min) @ Ic, Vce420 @ 2mA, 5V

BC547B says

DC Current Gain (hFE) (Min) @ Ic, Vce200 @ 2mA, 5V

So my newbie pedal building brain (and big time metalhead, high gain guy mentality) says to me that the BC550C has more than twice the gain of the BC547B aka would have more OUTPUT when the knobs are spun?  I could be very wrong on this of course.

And yes!  I WOULD LOVE TO TRY SOME DIFF ONES.  Do you happen to have any BC550C?  When possible I try to use the *exact* parts defined in the PCB build list.  It was not until after buying the ISCOCELES that I hit the BC550C conundrum.  I am also building a sprit box reverb and thankfully was able to find the Belton BTDR-2H - Reverb IC LONG at stompboxparts.


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## fig (Sep 5, 2021)

I don't have a 550C, but they can be had here;



			https://www.tubesandmore.com/products/transistor-bc550-b-92-case-npn
		


They also have 5089s. 

And/Or, I would be happy to send you a couple alternates just to hear. Shoot me your address in DM.


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## burger-patty-and-bacon (Sep 5, 2021)

fig said:


> I don't have a 550C, but they can be had here;
> 
> 
> 
> ...


Sweet.,,  I will send you my addy!  And that link you sent is for a BC550B which I can find - it is the BC550*C* that I cannot find except for eBay in larger quantities and high ship.


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## fig (Sep 5, 2021)

oh yeah...my bad. 









						BC550C High Gain NPN Fuzz Silicon Transistor
					

BC550C High Gain NPN Fuzz Silicon Transistor



					www.pedalhackerelectronics.com


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## mnemonic (Sep 6, 2021)

Maybe doesn’t help but my real tc integrated preamp has a bc413c for that transistor.

it also has a bc547b for the constant current source (schematic specs bc548b) but that part is excluded from the isocoles schematic. Apparently that part was wired incorrectly in the original 33 pedal (and therefore in the Triangulum also) and thus just left off for the isocoles.

not sure if the integral / Tc preamp have it wired correctly (or even what it is supposed to do!)


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## burger-patty-and-bacon (Sep 6, 2021)

mnemonic said:


> Maybe doesn’t help but my real tc integrated preamp has a bc413c for that transistor.
> 
> it also has a bc547b for the constant current source (schematic specs bc548b) but that part is excluded from the isocoles schematic. Apparently that part was wired incorrectly in the original 33 pedal (and therefore in the Triangulum also) and thus just left off for the isocoles.
> 
> not sure if the integral / Tc preamp have it wired correctly (or even what it is supposed to do!)


Interesting...   Bc413c looks to have similar if not more "gain" than bc550c.  I'm still a noob to pedal builds so my amateur guess is that this specific transistor would have a pretty huge impact on how the ISOCELES sounds, yes? I read in the ISOCELES review some dude said his output was low....  Perhaps he used a low gain BCxxxx IC??

I am a huge fan of boosts into high gain amps and right now I am using my own PLUMES build to goose my Mark 5 25 head which is in the iic mode.   I like very very very tight start/stop metal tones.  I have never used a real 33 or a real TC intepre.  I have used software emulations but we won't get into the real vs sim debate.


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## mnemonic (Sep 6, 2021)

burger-patty-and-bacon said:


> Interesting...   Bc413c looks to have similar if not more "gain" than bc550c.  I'm still a noob to pedal builds so my amateur guess is that this specific transistor would have a pretty huge impact on how the ISOCELES sounds, yes? I read in the ISOCELES review some dude said his output was low....  Perhaps he used a low gain BCxxxx IC??
> 
> I am a huge fan of boosts into high gain amps and right now I am using my own PLUMES build to goose my Mark 5 25 head which is in the iic mode.   I like very very very tight start/stop metal tones.  I have never used a real 33 or a real TC intepre.  I have used software emulations but we won't get into the real vs sim debate.



I’m not sure how much of a sound difference it would make, I don’t have the isocoles but I did build the integral pre as it has an on/off switch unlike the original integrated preamp. They pretty much sound the same (allowing for pot taper differences), the integral being maybe slightly higher output when volume is on maximum. The integral I’m pretty sure I built with the bc548c spec’d in the build docs.

I did do some op-amp swapping, tl071, lm741, and the burr brown opa604, I didn’t hear any difference, even there. Though it’s run totally clean so not too surprising. It’s not like a Rat where the op amp clips significantly.

I’ve got a ton of boosts, I’ve always been a big recto fan and recto’s take overdrives and boosts very well. I was super into the meshuggah chaosphere/DEI type tone for a long time, which the integrated preamp does very well. Though lately I’ve really been digging just a stock ts9 for a looser but chuggier tone.


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## benny_profane (Sep 6, 2021)

I think that increased hFE will give you diminishing results. The topology is a bit difficult for me to parse here since it interacts with the op amp feedback loop, but I think if you increase the hFE, you’ll get more prominent high freqs more than anything else. Just be mindful of the pinout and the voltage rating. Socket the part and try out different devices.


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## bowanderror (Sep 6, 2021)

I've been using BC549C as my high gain NPN of choice for a while and it's a good general purpose replacement. It was tough to get 2N5089 for a bit, and the BC549C slotted in nicely. It's widely available, even from cheap vendors, and the specs have been quite close between lots.

I believe BC548, 549, & 550 are just binned versions of the same die. BC546/547 may be as well. 549/550 are selected for lowest noise bins, 546 high voltage, and 547/550 medium voltage: https://www.mouser.com/datasheet/2/149/BC549-888525.pdf


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## burger-patty-and-bacon (Sep 6, 2021)

bowanderror said:


> I've been using BC549C as my high gain NPN of choice for a while and it's a good general purpose replacement. It was tough to get 2N5089 for a bit, and the BC549C slotted in nicely. It's widely available, even from cheap vendors, and the specs have been quite close between lots.
> 
> I believe BC548, 549, & 550 are just binned versions of the same die. BC546/547 may be as well. 549/550 are selected for lowest noise bins, 546 high voltage, and 547/550 medium voltage: https://www.mouser.com/datasheet/2/149/BC549-888525.pdf


Thanks for all the feedback


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## Chuck D. Bones (Sep 7, 2021)

benny_profane said:


> I think that increased hFE will give you diminishing results. The topology is a bit difficult for me to parse here since it interacts with the op amp feedback loop, but I think if you increase the hFE, you’ll get more prominent high freqs more than anything else. Just be mindful of the pinout and the voltage rating. Socket the part and try out different devices.


TC Electronics put that transistor in front of the opamp because they used 741's in their original production units.  Among all of their other shortcomings, 741s are noisy and putting a transistor there the way they did goes a long way to solving that problem.  It's like a 3rd nipple now that everyone uses TL072s.  The HFE of that transistor affects the biasing and that's all.  Higher HFE is better, but once you have enough, more doesn't make it better.  As long as the opamp's output is somewhere around 14 or 15V you're good.  MPSA18, 2N5210, 2N5089, BC549C are all low-noise and have sufficient HFE.  That transistor is inside a high-gain feedback loop; the Rs and Cs in that loop determine the freq response.


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## fig (Sep 7, 2021)

I've put you a sample pack together to audition. Some have lower hFE than you are after but I included a few just so you'd have them. 

In no particular order;

BC550-293
BC319B-275
2N5089-501
2N2N24-203
BC549C-503
2N5088-561
2N3565-296
BC109C-624
BC108C-687
MPSA14-641
MPSA18-32000
MPSA13-31900


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## burger-patty-and-bacon (Sep 7, 2021)

fig said:


> I've put you a sample pack together to audition. Some have lower hFE than you are after but I included a few just so you'd have them.
> 
> In no particular order;
> 
> ...


Holy wow.  Thank u!!!


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## Feral Feline (Sep 7, 2021)

I always wondered what Santa does in his off season: he builds pedals while masquerading online under the pseudonym "Fig".

C'mon Fig, stop mucking about with pedals and start prepping for Christmas — my niece and nephew will each be six (twins), and have been good, well the niece for sure and the nephew mostly... For myself, well the usual coal in stocking will suffice. At least this coming season I can use it to keep warm...


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## Mcknib (Sep 7, 2021)

Feral Feline said:


> I always wondered what Santa does in his off season: he builds pedals while masquerading online under the pseudonym "Fig".


And don't forget my bike one of these will do





But in lake placid blue if you can manage it Santa...I mean @fig With a skull gear stick please

You should maybe change yer username to Fanta the Fig version of Saint Figolas

Obviously wear an orange santa suit


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## fig (Sep 7, 2021)

I can only see a bit of the sissy bar and handlebar at the top, but I am guessing it's an Schwinn Orange Crate?


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## Chuck D. Bones (Sep 7, 2021)

fig said:


> I've put you a sample pack together to audition. Some have lower hFE than you are after but I included a few just so you'd have them.
> 
> In no particular order;
> 
> ...


I think you have the HFE switched between the MPSA14 and MPSA18.


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## fig (Sep 7, 2021)

Thank you sir!


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## Feral Feline (Sep 7, 2021)

fig said:


> I can only see a bit of the sissy bar and handlebar at the top, but I am guessing it's an Schwinn Orange Crate?
> 
> View attachment 15772



STOP SQUINTING, and put on your reading glasses.


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## fig (Sep 7, 2021)

That's not a bicycle. That's a chopper, baby!


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## Mcknib (Sep 7, 2021)

fig said:


> That's not a bicycle. That's a chopper, baby!


Raleigh 3 speed no less the excalibur of bikes 

Mine had dodgy brakes not too kind on yer crown jewels when you flew over the handlebars and left them behind


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## Feral Feline (Sep 7, 2021)

My brother's Raleigh Chopper was Purple. 

I had to make do with that saddle aftermarket along with the sissy bar and handlebars. Alas, my bike was later stolen, or I'd be one of those adults riding his "lowrider" bike around car shows...


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## HamishR (Sep 9, 2021)

My bike was the other way around. Classic "dragster" frame ala Schwinn, 20" rear wheel and a 26" front wheel. Made it out of parts over a few months and rode it everywhere. Sprayed it matt black, it had a low rise sissy bar and handlebars - never cared for ape-hangers.

Now all these years later I have a Triumph Bonneville in matt black and M-bars.  Some things never change!

And for what it's worth I've used BC550Cs and BC549Cs as subs for each other and never really noticed any difference. Same with 2N5088s and 2N5089s.  I bought stacks of the BCs from Mouser - they may still have them.


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## burger-patty-and-bacon (Sep 11, 2021)

fig said:


> I've put you a sample pack together to audition. Some have lower hFE than you are after but I included a few just so you'd have them.
> 
> In no particular order;
> 
> ...


Huge huge mega thanks to Fig for sending me all of these chips!!   So cool and kind.   I just got my 5 PCB from PedalPcb yesterday along with my big $100 tayda order.   I paid for FedEx and got my tayda package IN TWO DAYS!!!   THANKS AGAIN FIG.  SO COOL OF U.


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## bowanderror (Sep 11, 2021)

HamishR said:


> My bike was the other way around. Classic "dragster" frame ala Schwinn, 20" rear wheel and a 26" front wheel. Made it out of parts over a few months and rode it everywhere. Sprayed it matt black, it had a low rise sissy bar and handlebars - never cared for ape-hangers.
> 
> Now all these years later I have a Triumph Bonneville in matt black and M-bars.  Some things never change!
> 
> And for what it's worth I've used BC550Cs and BC549Cs as subs for each other and never really noticed any difference. Same with 2N5088s and 2N5089s.  I bought stacks of the BCs from Mouser - they may still have them.


BC550 & 549 are both selected for low-noise, so you won't notice a difference, especially with a guitar pedal. Where you are more likely to notice a difference is between A/B/C hFE (gain) classification, and it would only affect circuits that rely on that particular gain range.





In general, BC546/547/548/549/550 are all interchangeable as long as the A/B/C gain bin is the same. The exceptions would be:

*High voltage* (>30V Collector to Emitter) - BC546 up to 65V, or BC547/550 up to 45V
*Need lowest noise* - BC550 is lowest noise, BC549 second lowest (all others higher)
This kind of question gets easier to answer once you know what to look for. The datasheet is the place to go, and looks a bit intimidating, but actually isn't that bad. I usually look for the differences between different part numbers or A/B/C ratings.

The max voltage rating can be found in the Absolute Maximum Ratings table (Vceo = voltage between Collector & Emitter pins):




Info on in-circuit voltages, noise performance, gain bandwidth and hFE (gain) is in the Electrical Characteristics table (hFE is directly below this):




Usually if BJT transistors are on the same datasheet (same series), they are "binned" components, meaning they are the same components that have been tested after manufacturing to select the best performing parts. Binned BJTs are often sorted for things like hFE, voltage ratings, & noise performance.


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## burger-patty-and-bacon (Sep 13, 2021)

Thank you.  Much to learn - very helpful!


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