Re: LF: Sound Card Impedance

["Clemens Paul" <cpaul@gmx.net>]

Rik,

 

>I have measured a significant C (up to some nF) in parallel to R at the input of some soundcards.

I can confirm this.

I've digged out a VNA plot (starting at 5kHz) of my onboard soundcard.

You can see that at 10kHz  Z is around 3kOhm, R 2,5kOhm 

and parallel C around 2,9nF.

The 4kOhm Z-number I've mentioned in my previous posting was

measured (IIRC) around 1kHz using the 6dB method with a pot

and a sig gen. 

 

73
Clemens
DL4RAJ

 

 

----- Original Message -----

From: "Rik Strobbe" <Rik.Strobbe@fys.kuleuven.be>

To: <rsgb_lf_group@blacksheep.org>

Sent: Thursday, December 16, 2010 2:13 PM

Subject: RE: LF: Sound Card Impedance

Johan,

at what frequency did you measure.
I have measured a 
significant C (up to some nF) in parallel to R at the input of some 
soundcards.

73, Rik  ON7YD - 
OR7T


________________________________________
Van: owner-rsgb_lf_group@blacksheep.org 
[owner-rsgb_lf_group@blacksheep.org] namens Johan H. Bodin 
[jh.bodin@telia.com]
Verzonden: donderdag 16 december 2010 13:26
Aan: 
rsgb_lf_group@blacksheep.org
Onderwerp: Re: LF: Sound Card Impedance

I measured the input 
impedance of the mic input on a Dell laptop:

AC input impedance: 4.3 
kOhms (-6dB with 4k3 resistor in series)
Mic bias voltage: +3.8V (open 
circuit)
Output current: 809uA (shorted to GND)

This suggest that 
there is a 4k7 pull-up resistor to +3.8V for mic DC bias.

It may vary 
somewhat between different brands and models of course but all
soundcard mic 
inputs that I have seen so far puts out some DC bias for 
electret
microphones.

73
Johan SM6LKM

----

Ken 
wrote:
> Hello all.
> Does anyone know the approximate impedance of 
the mic input jack on a pc sound card.
>
> 73.
> Ken
> 
M0KHW

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