Problem with DI box

[Coolhat]

Hi,

I´m building a passive DI box for my bass rig, using the Lundahl LL1935-transformer. I´ve wired it using a diagram from the vendor´s site:

Now, with my active bass guitar sound is coming through fine, but with a passive bass there is a significant treble roll-off. I´m guessing this has something to do with impedance? Any ideas on how to fix this?

 

[epicyclic]

Microphone inputs are generally low impedance do have line inputs you can try .

 

[JonSnell Electronic]

Connect 1 & 3 together, centre tap.

Connect 2 to ground/screen of guitar jack.
Connect 4 to signal guitar jack tip.
Connect 7 & 5 together.
Connect 8 to preamp signal jack tip.
Connect 6 to E and screen to preamp jack.
That will give you line level output.
For Mic level, wire the outputs;
8 & 5 together, +
7 & 6 together -
E is screen.

 

[turk 182]

JonSnell's advice is spot on, only thing i noticed in the original wiring scheme was the two primaries where out of phase/polarity.

 

[Coolhat]

Hi again and thanks for the replies!

I re-wired the transformer the way Jon suggested (the mic level version) but unfortunately there is no noticeable change. The sound is still very dark. I am starting to wonder if there is something wrong with the trafo?

 

[klingo]

Hi, may be wrong, but aren't you using it as a stepping up transfo, which mean 25 or 100 time less reflected Z to your instrument (1/5 or 1/10) ?

 

[dotneck335]

If the diagram is as posted in #6, it seems to me that the instrument should go to the HIGH impedance side----between 8 and 6, with 5 & 7 tied. The input to the mixer should come from the LOW impedance side---1 & 4 tied together, 2 & 3 tied together, the output from 1 &4 (HOT side) and 2&3 (COLD side). This will provide the guitar pickup with the highest load, and the mixer will see a low impedance, like a microphone.

 

[Coolhat]

If the diagram is as posted in #6, it seems to me that the instrument should go to the HIGH impedance side----between 8 and 6, with 5 & 7 tied. The input to the mixer should come from the LOW impedance side---1 & 4 tied together, 2 & 3 tied together, the output from 1 &4 (HOT side) and 2&3 (COLD side). This will provide the guitar pickup with the highest load, and the mixer will see a low impedance, like a microphone.

OMG, I think you are right! I checked out the datasheet and it had these diagrams:

I might be wrong, but aren´t these the exact wiring schemes Jon proposed, just inverted?

 

[turk 182]

yup!