burger-patty-and-bacon
Active member
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
Which one is the highest gain of those 3 - how would I determine that?
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.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.
DC Current Gain (hFE) (Min) @ Ic, Vce | 420 @ 2mA, 5V |
DC Current Gain (hFE) (Min) @ Ic, Vce | 200 @ 2mA, 5V |
Sweet.,, I will send you my addy! And that link you sent is for a BC550B which I can find - it is the BC550C that I cannot find except for eBay in larger quantities and high ship.I don't have a 550C, but they can be had here;
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.
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??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.
Thanks for all the feedbackI'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
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.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.
Holy wow. Thank u!!!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