Return-Path: Received: from mtain-dg08.r1000.mx.aol.com (mtain-dg08.r1000.mx.aol.com [172.29.65.16]) by air-dd01.mail.aol.com (v129.4) with ESMTP id MAILINDD011-86074d0a05cdb1; Thu, 16 Dec 2010 07:27:57 -0500 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-dg08.r1000.mx.aol.com (Internet Inbound) with ESMTP id 8472F38000178; Thu, 16 Dec 2010 07:27:51 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1PTCvF-0004P3-9q for rs_out_1@blacksheep.org; Thu, 16 Dec 2010 12:27:01 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1PTCvE-0004Ou-Ur for rsgb_lf_group@blacksheep.org; Thu, 16 Dec 2010 12:27:00 +0000 Received: from smtp-out21.han.skanova.net ([195.67.226.208]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1PTCvC-0004T5-Bt for rsgb_lf_group@blacksheep.org; Thu, 16 Dec 2010 12:27:00 +0000 Received: from [127.0.0.1] (81.235.167.68) by smtp-out21.han.skanova.net (8.5.133) (authenticated as u33233109) id 4D075171000FAA6A for rsgb_lf_group@blacksheep.org; Thu, 16 Dec 2010 13:26:52 +0100 Message-ID: <4D0A058E.4010103@telia.com> Date: Thu, 16 Dec 2010 13:26:54 +0100 From: "Johan H. Bodin" User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; sv-SE; rv:1.9.2.13) Gecko/20101207 Thunderbird/3.1.7 MIME-Version: 1.0 To: rsgb_lf_group@blacksheep.org References: <5BB571709EEB4C2084239E924B0EACEE@lindavideo> In-Reply-To: <5BB571709EEB4C2084239E924B0EACEE@lindavideo> 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 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-sid: 3039ac1d41104d0a05c70c33 X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none X-Mailer: Unknown (No Version) 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