which one more hi gain?

[teddybear]

2n7000 or bs170?
for metal head

thx

[Mark Hammer]

Neither.  The gain is set by how it is configured, not by the transistor itself.  What is inherent in the transistor is how much gain you can ask it to provide...via the configuration.  Same with op-amps.

[teddybear]

ok. which one more low noise? bs250, bs170 dan 2n7000?

[brett]

You might not want to hear this...

But noise is also affected by configuration, especially for JFETs and CMOS. I'm fairly sure that both goups are noisier than BJTs, and the noise is strongly related to current flow.  I wish I could remember whether it's a positive or negative relationship!  Anyway, it'll be on the datasheets.