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References: <5BB571709EEB4C2084239E924B0EACEE@lindavideo> <4D0A058E.4010103@telia.com> <4D0A182E.7050900@iup.uni-heidelberg.de>
Date: Thu, 16 Dec 2010 05:59:00 -0800 (PST)
From: Daniele Tincani <danieletincani@yahoo.com>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: Sound Card Impedance
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Hi LF,

very interesting info. However, often the line input of a sound card is us=
ed to=20
connect a pre-amp (rather than the mic input which is more prone to overlo=
ad).=20
Am I wrong?

Best regards
Daniele



________________________________
From: Stefan Sch=E4fer <Stefan.Schaefer@iup.uni-heidelberg.de>
To: rsgb_lf_group@blacksheep.org
Sent: Thu, December 16, 2010 2:46:22 PM
Subject: Re: LF: Sound Card Impedance

Johan,

Am 16.12.2010 13:26, schrieb Johan H. Bodin:
> 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 bi=
as.
>
> 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=
=20
electret
> microphones.
>
> 73
> Johan SM6LKM
>

Interesting! Thank you for this information.

Maybe one should think about this when designing a sensitive preamp=20
output stage. I will keep it in mind.

73, Stefan/DK7FC


     =20

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<html><head><style type=3D"text/css"><!-- DIV {margin:0px;} --></style></h=
ead><body><div style=3D"font-family:arial, helvetica, sans-serif;font-size=
:10pt"><DIV>Hi LF,</DIV>
<DIV>&nbsp;</DIV>
<DIV>very interesting info. However, often the line input of a sound card=
 is used to connect a pre-amp (rather than the mic input which is more pro=
ne to overload). Am I wrong?</DIV>
<DIV><BR>Best regards</DIV>
<DIV>Daniele</DIV>
<DIV style=3D"FONT-SIZE: 10pt; FONT-FAMILY: arial, helvetica, sans-serif">=
<BR>
<DIV style=3D"FONT-SIZE: 13px; FONT-FAMILY: arial, helvetica, sans-serif">=
<FONT face=3DTahoma size=3D2>
<HR SIZE=3D1>
<B><SPAN style=3D"FONT-WEIGHT: bold">From:</SPAN></B> Stefan Sch=E4fer &lt=
;Stefan.Schaefer@iup.uni-heidelberg.de&gt;<BR><B><SPAN style=3D"FONT-WEIGH=
T: bold">To:</SPAN></B> rsgb_lf_group@blacksheep.org<BR><B><SPAN style=3D"=
FONT-WEIGHT: bold">Sent:</SPAN></B> Thu, December 16, 2010 2:46:22 PM<BR><=
B><SPAN style=3D"FONT-WEIGHT: bold">Subject:</SPAN></B> Re: LF: Sound Card=
 Impedance<BR></FONT><BR>Johan,<BR><BR>Am 16.12.2010 13:26, schrieb Johan=
 H. Bodin:<BR>&gt; I measured the input impedance of the mic input on a De=
ll laptop:<BR>&gt;<BR>&gt; AC input impedance: 4.3 kOhms (-6dB with 4k3 re=
sistor in series)<BR>&gt; Mic bias voltage: +3.8V (open circuit)<BR>&gt;=
 Output current: 809uA (shorted to GND)<BR>&gt;<BR>&gt; This suggest that=
 there is a 4k7 pull-up resistor to +3.8V for mic DC bias.<BR>&gt;<BR>&gt;=
 It may vary somewhat between different brands and models of course but al=
l<BR>&gt; soundcard mic inputs that I have seen so far puts out some DC bi=
as for
 electret<BR>&gt; microphones.<BR>&gt;<BR>&gt; 73<BR>&gt; Johan SM6LKM<BR>=
&gt;<BR><BR>Interesting! Thank you for this information.<BR><BR>Maybe one=
 should think about this when designing a sensitive preamp <BR>output stag=
e. I will keep it in mind.<BR><BR>73, Stefan/DK7FC<BR><BR></DIV></DIV></di=
v><br>

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