[LAU] checking passive input frequencies on non Hi-Z connection

[Dominique Michel]

Le Fri, 26 May 2017 21:30:59 -0400,
"Wayne DePrince Jr." <waynedpj at ingiro.xyz> a écrit :

> ahoy all,
> 
> however, as
> i mentioned, some of these interfaces i am also testing out (e.g.
> Edirol FA-66, Zoom U-44) have a Hi-Z button on an input which
> supposedly allows direct inputing of a passive signal.  is this Hi-Z
> button just enabling some internal DI box or preamp?  are there
> drawbacks to using it instead of using an actual DI box, preamp,
> etc?  seems like just another way to match that signal to something
> expected by the input, but again i am still wading my way through all
> this.

It depend how it is done in the hardware. A typical guitar amp input
have an impedance around 1MEG ohms and a very high sensibility (1.2
to 1.5 mV for full output at full volume). 

The high sensibility give the ability to saturate all the stages in the
guitar amp, but when using a computer, you will make that saturation in
software. A typical passive guitar microphone can output peaks around 1
volt, some will goes up to 2 volts peak. This imply the input of your
device must not only have an high impedance, but must also be able to
handle such peaks. For the impedance, a typical passive guitar
microphone impedance range between 10 to 15 k ohms, sometime less,
sometime more (higher impedance implies more turns in the microphone's
coil, which imply more signal amplitude). The input stage impedance must
be at least 10 times more than the microphone impedance. As a good
guitar mic is around 15 k ohms or more, the input impedance must be 150
k ohms or more.

Cheers,
Dominique

> 
> 	OK, thanks again for all your advice and help.
> 
> peace, w
>