Introducing... the UberBooster (discrete op-amp, sorta)

[earthtonesaudio]

Everything I personally could want in a booster.  High Zin, low Zout, doesn't invert the signal, and delivers a good range of clean-to-mean with a 100k gain pot.  Lots of output.
Started as just common drain/common gate/common drain buffer stages in series, but ended up looking a bit like a discrete op-amp in non-inverting configuration.

Note the middle transistor is a BS170.

[OnLyTNT]

Can we replace BS170 with j201 too? All j201 design I mean. Is it possible? Thanks for the schematic.

[earthtonesaudio]

I tried that also.  It does pass sound, but it doesn't really boost much.

[Purple People Eater]

That's really cool.

Jay Doyle designed a DISCRETE BOOST a while back, but it's quite a bit different. More parts, and a slight bit more complicated than yours. Still fairly simple and sounds good though.

I'll have to build yours soon. You may want to add some static protection for the BS170 though. See the AMZ Mosfet Boost or the SHO for examples.

Nice work !

(Oh, BTW: Did you try using a high gain BJT like a MPSA18 in place of the top J201 ? It would make for a nice low z out as well)

[earthtonesaudio]

Thanks for posting the link to the Doyle Discrete Boost.  I hadn't seen that before, it looks good.
MPSA18, that's a Darlington, right?  That would be a good idea.  I don't have any of those, but I'll have to try a high gain NPN there.

You could put in static protection, but I personally don't think it's necessary.

The thing I like about this circuit is that each of the trannys are doing a different job, yet they all help bias each other.  I'd personify it as a cooperative circuit.   

[Purple People Eater]

I hope that you don't mind my posting this layout. It should be correct. Let me know if you find any errors.

[earthtonesaudio]

No problem.  Looks good!  Thanks for drawing that up. 

Like most circuits with a really low parts count, this one is really responsive to parts values.  Right now I'm liking a .047uF cap for C1 a bit more than the .1uF I originally wrote.  Feel free to deviate from the values shown.