BC550C

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
 
"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?
 

benny_profane

Well-known member
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.
 
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!
 

fig

Well-known member
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.
 
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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mnemonic

Active member
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!)
 
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.
 

mnemonic

Active member
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

Well-known member
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.
 

bowanderror

Active member
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
 
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
 

Chuck D. Bones

Well-known member
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.
 

fig

Well-known member
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
 
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
Holy wow. Thank u!!!
 
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