line to mic level pad

[MLM]

hi there! just have a quick question i could do with some help - much obliged for any assistance offered...
I'm putting together a passive attenuator out of two 33k resistors with a 150ohm resistor across the two of them (to simulate a 150ohm load to the preamp) so that i can feed line level keys/rhodes etc into my seventh circle N72 neve-type preamp.... i was just wondering if i would get any problems feeding an unbalanced output into this arrangement? i.e the -ve side would be linked to earth.. also wanted to double check the resistor values i'm using would this be suitable for bass guitar/fender rhodes type outputs also? i know i should really use a passive DI box but budget is zero!!
thanks in advance!!

 

[Handcrafted Tone]

Here is some info you can research.

http://www.uneeda-audio.com/pads/

http://beradio.com/notebook/passive_attenuators/

The resistor values will be different if balanced or unbalanced. I built the resistors right into an xlr cable. I suggest a few different cables, some for your balanced line stuff, and others for your unbalanced instruments. Use the calculator in the second link to figure out R values for attenuation and impedance. You may want less attenuation on a guitar compared to a bass or keyboard.

 

[PRR]

> wondering if i would get any problems feeding an unbalanced output into this arrangement?

If the mike input is very good (that one is), then it will work just fine.

Especially transformer-input won't care.

If it is a transformerless input, it gets a common-mode voltage equal to half the line-level signal voltage. Some junky inputs can't stand more than a volt of common mode signal before they distort real bad. In that case, you should use 66K (75K) and 150 as an unbalanced pad, with one Mike input pin grounded.

Do be careful about Phantom voltage getting back into your Line Output. Some gear won't mind, but some gear will get very upset, maybe blow the output caps.