Line-DI.. Bo Hansens?

Hi there.

I need to do a 8ch DI box, for a live keyboard setup.
I've previously used 8 x OEP A262A2E as a "quick-fix" - as 1:1 just connected directly between jack, and XLR.

But now i would like to re-do it more correctly.
Since i already have the A2E's, i would like to use them again

Would it be possible to adapt Bo Hansens DI to the A2E, instead of the A3E?
Since its a keyboard setup, i assume the signals will be quite strong.
Some signals will come from delay-, or chorus-pedals. Some directly from modern keyboards

Do you think the level from the keys will be to high for the active Bo Hansen design?
Should I consider a passive setup instead ?

There will be a mains inlet in the box anyway, so it would be possible to have "normal" power-rails, instead of phantom-power..

I hope you guys can help me a little here 

I think it should work even with phantom power. Check with the others if second emitter follower would drive this kind of transformer and how it should be wired for best frequency response.

Eicen,

If this transformer is connected in the highest primary impedance, it becomes too low impedance to be driven by the emitter follower in my DI box with good headroom. Best result is 5k and up, the 26A2E have only the half impedance of this.

--Bo

Hi, thanks for reply, this is interesting because line out makes a lot of sense. Don't really know why modern DI's aren't mostly built this way, guess phantom doesn't have enough power or people don't want to take this step...
Would you suggest changing 2nd follower to something else, or change transistor and give it more current?

Thanks for your replies.
Maybe it would be best, just to use a TL072 to drive the transformer as 1:1?

..or wouldn't it be possible to adapt the output stage of the G1176?
I can't quite figure out, what the sensitivity is at "C10"..

You will have to choose transformer driver depending on the inputs (loads) it will drive. If they are lower than 2000 ohms you need NE5534 or another op amp that can drive this kind of loads. I guess your line inputs have 10k ohms or more, so TL071 or dual version TL072 should drive 1:1 transformer into them.
Here is good explanation of TL071 driving transformer:
http://www.audioasylum.com/audio/tweaks/messages/10/105872.html
As you are making proper psu i would rather buy another op amp or even THAT 1646 line driver to drive any kind of load. Check this forum for good examples with 1646 into 600 ohms:
http://www.proaudiodesignforum.com/forum/php/viewtopic.php?f=6&t=140
1176 output stage is a bit complicated for this simple task. C10 blocks DC current and sets lowest frequency, so you could wire your outputs into R27 potentiometer and take away C10 because there shouldn't be no DC from outputs.
Another thread about driving transformers directly from opamp is here:
http://groupdiy.com/index.php?topic=44520.0
And another about headphone drivers which are pretty similar to what you need. Maybe check fig.9b by PRR, it adds voltage driver IC and has class A mosfet source follower. This is even simpler and might sound better than class A/B  symetric emitter followers:
http://headwize.com/?page_id=147

So let us know if you might ever encounter 600 ohms inputs (1176, LA2A, Pultec...). Based on this we can give you better answer. I had good results with THAT 1646 into Edcor transformer, unfortunately Farnell only carries SMD version instead of DIP.

Thanks for your reply.

I'll will mostly be facing modern live-mixing desks, with relatively high input impedance.

I was looking at the output of the LA4, and thought that might work..
Not sure if i need a buffered unbal out, or if it would be enough to do a normal direct "thru" output..

LA4 output should work for your needs, is there any particular reason you want it? If it is for sound you might not get it with this transformers and it is also more complicated than other solutions.
Bo's DI buffers unbal. out because of impedance. I'm not sure how schematic you show works, especially part where it splits to unbal. out and trafo driver. Check this with others.
I would do 1646 driver for 8 channels because it is well documented, costs very little and you can try a few things. Even NE5534 would do for your impedances, or BUF634 with voltage opamp in front if you want more drive and avoid output transistors.
This kind of simple circuits are cheap enough to try several version. They are also so simple that you could try several versions on veroboard, and choose which one you like best.

Sorry to wake up this old topic, but it just became relevant again..

I've tried a new approach (just copied the input-stage from GSSL4000)
Do you think that the NE5534 is powerfull enough to drive a OEP A262A2E (backwards)

Thanks! 

Hello,

Just to let you know, on a tour earlier this year I used a pair of Bo Hansen's with Cinemags for the main keyboard patch that was coming out of a MOTU I/O at line level and it worked great. I don't have first hand experience with the transformer you want to use, but I can attest that the circuit in it's standard configuration can handle line level.

Thanks!

Paul