BSIAB2 FET question

[Sock Puppet]

Can anyone shed any light on why two J201 FETs have been used in the second stage - i.e. what makes these more suitable than the 2N5457s used in the first stage?

And vice versa?

S.

[km-r]

the second mu-amp?? j201's clip earlier that 5457 so therefore it will provide more distortion...

[brett]

Hi
J201s have more transconductance, and in a mu amp, higher gain.  They also bias quite differently.
cheers

[erick4x4]

Just socket them and try both (you will have to rebias), as it can make a big difference.

Me personally, I don't need all the gain, and like the sound of all 2n5457's in the BSIAB. Slightly brighter, and a little less gainy, but still plenty to crank.

[Jobet]

During the time when there was no local importer of J201s where I am, I was forced to DIY these emulator pedals (JCM800 and English channel) using 2N5457's.

They were a bitch to maintain, with the bias voltage always drifting and causing the pedal to sputter. Needless to say, it required constant readjusting of the bias trimmers.

And worse, the volume output was lower than unity. So I shelved them for a while.

Now that J201s are readilly available here, I can now revisit them and stick in the appropriate semiconductors

[Sock Puppet]

Thanks for the replies.

The main reason I asked is because I'm half way through populating a board and I've got a pokefull of 2N5457s but 0 J201s.

But you've given me plenty of food for thought.

Cheers,

S.