[airtech]

I have some racked 312's and would like to add a line input.   I'm using the 1538xl for the input transformer and was wondering if there was anyway to put some sort of inline pad before the preamp to accept the line impedance.  The signal distorts without any pad so I'm thinking that the level is a lot hotter.  Maybe like a 40 to 50 db pad.  

The box is a little to tight for me to do any modification on the 312 cards.

Any ideas what would work here?  Thanks.

Like this DI mod from Bo Hansen?
http://web.telia.com/~u31617586/#API%20312%20mic%20amp%20with%20DI%20input%20modification

[mattmoogus]

Make a U pad with 2x 470ohm resistors and a 120ohm shunt.  Thatll give you roughly 20db which will allow your 1538 to accept nearly +30 (off the top of my head) before clipping.  If the 312 circuit's min gain is more than unity then you might need to increase the pad value.

You could also build a higher impedance pad if you dont think your line source can drive 600ohms.

You can build it with a DPDT switch inside your box or into a female to male inline XLR adapter which you just plug between your line output and the mic in.  



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[gar381]

Hi airtech

Check out how Fabio does it.

http://www.thediypill.phx.com.br/forumfiles/R312sch_rev3.pdf

Works well

GARY

Here's a cool pad calculator. http://www.rapco.com/catalog/tpad.html

Choose console output (600 ohms) for the input. Choose mic (150 ohms) as the output and choose the level of attenuation. Typical is 40 dB.

You'll want the H-pad values.

Cheers,

elco

[kato]

This is a newbie question I know but, looking at Fabio's schematic, is this all that is required to add a line in to a 312?



(and the 2 leads at the right just go into the input transformer pos. and neg.)

Once I subtract all the pad and polarity stuff, this seems to be all that is required.
Will this work?

Thanks, Kato

[mattmoogus]

Thats all ya need!


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