Transistor Substitution

[Jer]

Hello,

I have a Madbean Freeloader Octave Fuzz on the bench. The EHX lizard queen is based off this circuit (see what I did there).

Q4 in the BOM is a 2n3906 transistor.

I dont have one. I believe this is a PNP Transistor. But I have some spicy PNP oddities in my stash.

I believe I can sub in a PNP transistor. My options:

P416B PNP Germanium - i have one with gain of 40-50 or one with 60-70 hFE

Or

BC178C telefunken antique with an hFE of 414.

So either too high gain or too low gain - either way lots of mojo.

I am working my way through a batch of Madbean builds. They are stellar. This PCB was an impulse click during checkout so I am not super fussed if it turns out on the wild side. Its a fuzz pedal after all.

Before you tell me to socket it and see what i like, its great advice. I dont have sockets. If i put this off until my next parts order i may as well follow the BOM and whats the fun in that.

Looking for confirmation and recommendations,

Also - hopefully this is the right thread.

Thank you

 

[jwin615]

416b is germanium, may work fine depending on leakage.
If it's just the one transistor, just stick them in there, minding the pinout, and try to get enough of a friction for to audition them. Assuming there's clearance around them, it's nothing to solder in transistors from the top side if needed.

 

[Jer]

Oh cool. Didnt realize i could do that, but that makes sense, i can absolutely solder from the top.

 

[Feral Feline]

2N3906 is PNP, max hFE up to 300
Subbing it out, I'd suggest trying a similar hFE, but don't limit yourself to that, just use whatever sounds good.

If you have any of the following you could try (Si)...
Transistor hFE
2N2907A 300 Complement to the 2N2222
2N4125 300
2N4208 120
2N4402 250
2N4403 500
2N5087 800 Complement to NPNs 2N5088 & 5089
2N5401 240
AC125 45 avg
AC128 50 avg
BC516 30k DARLINGTON
BC557B 450
BC558 800 Compliment to NPN BC548
BC559
BC560 450
BC640 250
MPSA64 10k–20k
PN2907A 300
...



(Ge)
2N404 hFE?
GT309G hFE avg 87.7, 88, 89.5, 92.1, 93.7
GT402B 90–125
OC44 Ge
OC71 Ge
...

 

[PedalBuilder]

If I recall correctly, the PNP transistor is part of the octave generator, which in turn is a copy of Tim Escobedo’s Push Me Pull You octaver. Someone else used a PNP germanium transistor in their Push Me Pull You and I think that it sounded pretty cool:

 

[Jer]

Thank you all for your insights. The results are in:

It sounds like a hornet with diarrhea and I love it.

Ended up going with a 2N527 Germanium in Q4. My build skills are primitive so I crossed my fingers and one-shotted it. It works.

Madbean has an alternate diode on a switch so I flipped it to let it shine.

This was my first build from left over parts so it’s living up to its freeloader and mr mojo rising monickers. I dont have the technology to provide a sound bite.

Cheers

 

[Feral Feline]

...

It sounds like a hornet with diarrhea and I love it.

...

Awesome!
Very happy for you. Need to have a graphic of that put on it some how...




Pity about the sound-bite, would love to hear what Hornet Diarrhoea sounds like.

 

[Jer]

Awesome!
Very happy for you. Need to have a graphic of that put on it some how...

View attachment 93996


Pity about the sound-bite, would love to hear what Hornet Diarrhoea sounds like.

Hahaha - thank you for the image! I will try and figure out a way to get that on this thing, if i can get my shit together

I just noticed when the clipping LED is engaged it brightens when the signal is active and dims when its not. This is probably not new info for this crowd and makes sense for its purpose but a cool little novelty to discover on my own.

 

[Feral Feline]

Hahaha - thank you for the image! I will try and figure out a way to get that on this thing, if i can get my shit together

I just noticed when the clipping LED is engaged it brightens when the signal is active and dims when its not. This is probably not new info for this crowd and makes sense for its purpose but a cool little novelty to discover on my own.

It's a popular thing to make the eyes/pupils in a graphic the clipping LEDs, such as in a Turbo Rat...


NOT MY BUILD! Just something I found online to illustrate the point. Note the bypass LED, so the "eyes" are definitely the clipping LEDs (sometimes "eyes" are used just for bypass).

 

[gonzo]

If I recall correctly, the PNP transistor is part of the octave generator, which in turn is a copy of Tim Escobedo’s Push Me Pull You octaver. Someone else used a PNP germanium transistor in their Push Me Pull You and I think that it sounded pretty cool:

Ha that was me years ago. Honestly I hear less of a difference between the silicone and germanium now