Passive guitar signal pad circuit

[deiseldave]

Hello everyone. I’m trying to find a simple circuit scheme that would allow me to attenuate a guitar signal before going into an audio interface.
The problem I’m trying to fix is a design shortcoming in a Presonus audio interface where even a passive guitar plugged directly into the instrument input clips bad even with input turned all the way down.
The Presonus also has an input Z of 500k, which sounds a little dark to me. In my head, I am imagining sole thing like a little box with a quarter inch female jack on each end, 1M input impedance, a voltage divider with a volume knob, and an output that would line up ok with the Presonus 500k in.
Even a guitar cable with some strategically soldered resistors seems like it could work. If I could knock the signal down about 9 to 12 DB, it would be in the ballpark.
Spent a good while looking for a design that would work. No luck.
Thanks in advance for any help.

[martin manning]

I think a buffer would be the best bet. Something like this, with a 1M to ground on the input and a level pot on output 2 (see middle of page). http://www.muzique.com/schem/mosfet.htm

[deiseldave]

Thank you, Martin.

[Stevem]

Sonething is way wrong here!
That input that you're using even though it's marked for instrument must be set for mic input if it's clipping that hard.

Is this input you're using a XLR or a 1/4" jack?

The hottest passive guitar output level I have ever seen is about .250 vac.

Zero dB line level is .775 vac and even active type guitars do not output that much.

Mic level starts at around 34 dB which is .006 vac.
This is a long ways from the .250 vac output of a hot guitar pickup!!!

I also can understand why you can't simply use the guitar's volume control since it's 100% the same as if you had made up a resistive attenuator.

[Reeltarded]

VERY wrong. Have you tried a direct box on a mic input?

I think you might have a gain cranked in the software setup for your device?