Help sourcing Transistors for Twin Face.

[giovanni]

I prefer matching gains in a Silicon FF. hFE is all that matters and parts numbers are irrelevant.

Typically, matching hFE gives smoother fuzz while asymmetrical hFE gives more characteristic square wave distortion and a more aggressive character.

The asymmetrical hFE thing as a general rule in Fuzz Faces is pure myth though with respect to Ge or Si Fuzzes. At least as it’s bandied about for matching devices or achieving “that” sound.

I can’t quite understand why matching hfe would do that, does it have to do with the feedback loop?

 

[Big Monk]

Is there a general rule of thumb as to what constitutes matched vs asymmetrical? I’m assuming that matched doesn’t literally mean exactly the same.

Matched to me is +/- 10% hFE.

Asymmetrical to me is where Q2, at least in silicon, is over 100 hFE higher.

 

[Big Monk]

I can’t quite understand why matching hfe would do that, does it have to do with the feedback loop?

I won’t BS you by saying I know exactly why either.

That’s what my ears tell me though.

That answer is in the relationship between Q2 hFE and how it’s coupled to Q1 through the feedback resistor. I imagine there are important relationships between the flow of current between them depending on the hFE value of Q2 and that informs the differences in distortion characteristics.

 

[giovanni]

I won’t BS you by saying I know exactly why either.

That’s what my ears tell me though.

That answer is in the relationship between Q2 hFE and how it’s coupled to Q1 through the feedback resistor. I imagine there are important relationships between the flow of current between them depending on the hFE value of Q2 and that informs the differences in distortion characteristics.

Maybe a simulation is in order…

 

[Coda]

Maybe a simulation is in order…

I thought we were already living in one, no? We are all just on a breadboard in Chuck’s Boneyard…