Help - Tube Preamp Balanced Opamp Line Out

[ncusack]

Hello,

I'm wondering if anyone here has experience adding a balanced opamp line driver to a tube preamp. I know that typically a transformer would be the choice for this kind of setup but im curious what results could be had with an opamp instead. I'm wondering if it could be added to something like an Alembic F2B in order to drive the signal to a mixing board.

Let me know what might be possible.

Cheers,

Neill

[GibsonGM]

It is possible. I think you might find the tone crappy, though, without the effects of the OT and speaker(s).  A lot of the magic of a tube amp comes from power tube distortion and how the OT and speakers color the sound.

At any rate, Merlinb is very good at coming up with this sort of thing....maybe we can lure him in here to answer your question!  I believe you'd need to use a trafo to do it right, but I don't have a ton of line-out experience....I limit those excursions to a couple of resistors to drop the level and away we go....

[ncusack]

Since this would be mated with a standalone tube preamp I'm not concerned with the OT and speaker options. I just want to add a balanced line out to run the preamp direct to a soundboard and hopefully drive a decent length cable. I found an example of the NEVE 1272 preamp herehttp://fivefish.net/diy/balanced/default.htm that will take unbalanced to balanced out. Could this be used to take the output from a tube preamp with something as simple as a voltage divider off the output?

[peterc]

http://twin-x.com/groupdiy/displayimage.php?album=487&pos=0

This is a balanced line driver project I have used many times.

Hope it works for you

Peter

[merlinb]

At any rate, Merlinb is very good at coming up with this sort of thing....maybe we can lure him in here to answer your question!

Something like this is what you're after. You just need to add a potential divider from the last tube stage, to make sure you can't send damaging voltages to the opamp (input protection diodes are advised). As shown this circuit needs a bipolar supply, but you could modify it for single rail, depdnding on your needs.

I found an example of the NEVE 1272 preamp herehttp://fivefish.net/diy/balanced/default.htm

Having worked on the 1272 I can tell you, whatever that is, it ain't it!  

[BubbaFet]

Jensen Transformers has a nice application note ...... http://www.jensen-transformers.com/an/an003.pdf
On the top of page 3, figure 2-4 is an interesting simple transformerless single-opamp stage balanced-output circuit diagram.