Return-Path: Received: from mtain-dc07.r1000.mx.aol.com (mtain-dc07.r1000.mx.aol.com [172.29.64.135]) by air-de07.mail.aol.com (v129.4) with ESMTP id MAILINDE071-5eba4d0a192b22c; Thu, 16 Dec 2010 08:50:35 -0500 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-dc07.r1000.mx.aol.com (Internet Inbound) with ESMTP id 7FB72380001BC; Thu, 16 Dec 2010 08:50:33 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1PTED7-0005RJ-6U for rs_out_1@blacksheep.org; Thu, 16 Dec 2010 13:49:33 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1PTED6-0005RA-R6 for rsgb_lf_group@blacksheep.org; Thu, 16 Dec 2010 13:49:32 +0000 Received: from relay2.uni-heidelberg.de ([129.206.210.211]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1PTED5-00054X-1Z for rsgb_lf_group@blacksheep.org; Thu, 16 Dec 2010 13:49:32 +0000 Received: from freitag.iup.uni-heidelberg.de (freitag.iup.uni-heidelberg.de [129.206.29.204]) by relay2.uni-heidelberg.de (8.13.8/8.13.8) with ESMTP id oBGDnUMj002772 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Thu, 16 Dec 2010 14:49:30 +0100 Received: from [129.206.22.206] (pc206.iup.uni-heidelberg.de [129.206.22.206]) by freitag.iup.uni-heidelberg.de (8.12.11.20060308/8.11.2) with ESMTP id oBGDnUeS031881 for ; Thu, 16 Dec 2010 14:49:30 +0100 Message-ID: <4D0A182E.7050900@iup.uni-heidelberg.de> Date: Thu, 16 Dec 2010 14:46:22 +0100 From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; de; rv:1.9.1.8) Gecko/20100227 Thunderbird/3.0.3 MIME-Version: 1.0 To: rsgb_lf_group@blacksheep.org References: <5BB571709EEB4C2084239E924B0EACEE@lindavideo> <4D0A058E.4010103@telia.com> In-Reply-To: <4D0A058E.4010103@telia.com> X-Spam-Score: 1.4 (+) X-Spam-Report: autolearn=disabled,RATWARE_GECKO_BUILD=1.426 Subject: Re: LF: Sound Card Impedance Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=none autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false x-aol-global-disposition: G x-aol-sid: 3039ac1d40874d0a19294d57 X-AOL-IP: 195.171.43.25 X-Mailer: Unknown (No Version) 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 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 > Interesting! Thank you for this information. Maybe one should think about this when designing a sensitive preamp output stage. I will keep it in mind. 73, Stefan/DK7FC