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Re: LF: Sound Card Impedance

To: <[email protected]>
Subject: Re: LF: Sound Card Impedance
From: "Clemens Paul" <[email protected]>
Date: Thu, 16 Dec 2010 21:05:55 +0100
References: <5BB571709EEB4C2084239E924B0EACEE@lindavideo>,<[email protected]> <BF4A524700075746A6467658DFC7102C88715AE9A2@ICTS-S-EXC2-CA.luna.kuleuven.be>
Reply-to: [email protected]
Sender: [email protected]
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" <[email protected]>
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:
[email protected] [[email protected]] namens Johan H. Bodin [[email protected]]
Verzonden: donderdag 16 december 2010 13:26
Aan:
[email protected]
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

Attachment: Soundcard_impedance.JPG
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