BC549B vs BC549C

[Giorfida]

I’m seeing the Kudzu uses BC549B as buffer transistors, and the Mystery Machine uses BC549C
In my lack of attention to detail, I bought a bunch of BC549C, and no BC549B. I know I can use the C in the Kidzu, but will it net any unexpected result? I know they are cheap enough, but I’d hate to eat the shipping on less than $0.50 worth of parts if I can get by with the BC549C with no noticeable problems

 

[BuddytheReow]

If it’s just as a buffer you can pretty much use any BJT.

 

[Giorfida]

If it’s just as a buffer you can pretty much use any BJT.

The maths are above my pay grade lol but it does look like a classic but buffer to me: emitter direct to to main power rail, base tied to Vref with resistor and output directly off of collector (which goes to ground through 10k resistor.

I know I could just buy the right BJTs, as they are only like $0.20-$0.30 each… I just hate shipping on something that small… not like I couldn’t find other parts/knobs/enclosures/wire etc to fill out an order lol

 

[giovanni]

The maths are above my pay grade lol but it does look like a classic but buffer to me: emitter direct to to main power rail, base tied to Vref with resistor and output directly off of collector (which goes to ground through 10k resistor.

I know I could just buy the right BJTs, as they are only like $0.20-$0.30 each… I just hate shipping on something that small… not like I couldn’t find other parts/knobs/enclosures/wire etc to fill out an order lol

Uhm that’s not a buffer. Usually in a buffer the output is at the emitter (emitter follower).

If the emitter is grounded there is no feedback, so the gain value is important. If there is a resistor on the emitter, it’s using feedback and the gain value won’t matter as much.

 

[Giorfida]

Uhm that’s not a buffer. Usually in a buffer the output is at the emitter (emitter follower).

If the emitter is grounded there is no feedback, so the gain value is important. If there is a resistor on the emitter, it’s using feedback and the gain value won’t matter as much.

Ack. I take it back. It’s collector to voltage rail, emitter to ground though 10k (and output off of emitter).
Sorry was sorting through some PNP geraniums earlier and my mind was in PNP land not NPN lol

 

[Feral Feline]

Have you a way of measuring the

Uhm that’s not a buffer. Usually in a buffer the output is at the emitter (emitter follower).

If the emitter is grounded there is no feedback, so the gain value is important. If there is a resistor on the emitter, it’s using feedback and the gain value won’t matter as much.

He's got his nomenclature mixed up. The BC569 trans are indeed buffers in the Kudzu.



AT Giorfida — do you have a way of measuring the hFE? (with your DMM or a TC-1 or similar)?

Just select some of the lowest gain "C"s you have and it should be fine. Probably fine with whatever gain BC549 you use, if you don't have a way to measure them.


Here's what I'd do: socket the suckers, and use what I have. Next time ordering something chuck in a few "B"s with the order and then I'm not out shipping fees for a piddly order. Swap 'm out easy peasy, see if there's a discernible difference with my own ears.


Also, you should note if you're building the Kudzu, MichaelW and Music6000 have some notes:

MichaelW says ( #13 ) it benefits from some mods:
Level: A100k (stock)
Gain: A1M (sub for B1M)
Tone: C25k (sub for B25K)
Presence: C10k (sub B10k)


MUSIC6000: https://forum.pedalpcb.com/threads/kudzu-overdrive-potentiometer-taper-changes.19738/
MUSIC6000: https://forum.pedalpcb.com/threads/kudzu-overdrive-pedal.19809/

 

[Giorfida]

Good idea on socketing! May do just that. Even if I don’t, I’ll just make sure to solder from the top so I can swap w/o pulling the board

I can test transistors with a tester I have. Not a high end atlas, but it should do just fine (I use it all the time for validating pinout on NOS germanium’s etc)

I did take note of the c taper pots, and have a few. I bet they would also make the zen drive and others like it a little easier to dial in

 

[giovanni]

As buffers, the gain won’t matter at all so either should work.