Adding DI out into Alembic tube pre

[Marko Ursin]

Hi all,
let me first introduce myself. I'm a Finnish teacher and free time bass builder. So far my highlights are  carbon fiber headless bass neck and 10-coil Wal-style pickups.
I've also made an Alembic tube bass preamp clone
http://music-electronics-forum.com/attachments/5388d1204940568-alembic_f2b_preamp.gif
I have a mosfet cathode follower in it to drop output impedance
http://i274.photobucket.com/albums/jj257/paintrdude/BassPREschem-1.jpg
Now I'd like to add DI output parallel to amp output. How would I do that? I guess some sort of tranformer would be needed but which one? Is there something else that needs to be done? I'm all thumbs when it comes to designing this kind of things so I'd be grateful if someone could help me out.

 

[okgb]

There are common 1:1 line transformers usually 10k or 600 ohm impedance , you can search the Jensen app notes on their site
I'm guessing with the mosfet device you don't need to use the actual " d.i. "  transformer for lower impedance as it would also
produce a mic level output,  you could also simply use another mosfet device to invert the polarity of the signal to give you the - part of
the + / - polarity of a balanced signal [ hot , cold & ground on xlr 3 pin ]  nice work btw !

 

[Marko Ursin]

So would something like Lundahl LL1527 work?
http://www.lundahl.se/wp-content/uploads/2013/05/1527_7xl.pdf

 

[okgb]

According to his spec sheet it looks like a pretty good all arounder
send the circuit to them and ask [ double check ] his opinion.

I like Lundahl and would buy them more but they become expensive in
North America

 

[Beachcoma]

I've built the same preamp, but without the MOSFET follower. With the output coming off the 12ax7 plate, the output impedance is roughly 40k.

What type of transformer would be necessary to produce a balanced D.I out, and what would be needed for a line level balanced out?

Robert