lundahl LL1935

[willie68]

Hi,
this is my first thread (beside the introduction), so please excuse, if i posted this into the wrong sub forum.

Beside the electronics, i play bass in a band. And for my board i need i good di box. So i bought a cheap one, Millenium DI-P (Millenium DI-P Passive DI-Box) just to have a prepared case.

Next step was to change the transformer. Because of some reasons, my choice fell on the well-available Lundahl LL1935. (https://www.lundahltransformers.com/wp-content/uploads/datasheets/1935.pdf)
After some research i found this nice schematics



on the disttrubutors web site. But now i'm really confused. Nomally i would say that the low impedanz side should be connected to the mic input. But if you look into the datasheet you will find that the side with the shielding pin is the high impedanz side (pins 5..8). So in this schematic, the high impedanz side is connected to the Mic and the low one is connected to the instrument. Is there something i have missed?
My actual schematic looks like this:

 

[volker]

Hi Willie! Yes your schematic is correct, the labels in the Don Audio drawing should be switched.

 

[willie68]

thanks for your opinion. Then I am reassured.

 

[chopkinsbassist]

Hi All,

I've bought a LL1935 for a passive DI box that I'm designing to attenuate the output from the preamp of my Ibanez bass by 30db as it's very hot when it hits my MOTU 8Pre interface, even with the onboard pad engaged and the gain turned all the way down. I've got an ART active direct box with two 20db pad switches. 20db isn't enough attenuation and 40db is too much, hence why I want 30db.

I would like the option to have switchable 20/30db attenuation so am I correct in assuming that R1 and R2 form a voltage divider to set the attenuation? Would I also be correct to assume that the input impedance of the 1935 is 650ohms? I used the equations on this page (L Pad Calculator + Speaker Attenuation Guide) and it suggests an R1 value of 629 ohms and R2 value of 21 ohms for 20db attenuation....are these practical values for a DI box? When I plugged the R1 and R2 values in the formula then I got an attenuation of 33db.

Sorry if I sound confused but the last time I had to seriously think about voltage dividers and stuff like that was approx 25 years ago in school!