BD139, BD140 - which brand?

[lordearl]

I notice STIMicro, Multicomp, ON Semi and Fairchild all currently manufacture these transistors - which is preferable for a headphone amp?

 

[amc184]

ST, ON and Fairchild should all be okay. Multicomp is not actually a brand at all, it's the label under which Farnell sells generic, no-brand stuff. For semiconductors in critical places, I'd avoid Multicomp.

Pressed to make a choice, I'd go with ON.