Return-Path: Received: from mtain-da12.r1000.mx.aol.com (mtain-da12.r1000.mx.aol.com [172.29.64.84]) by air-dd03.mail.aol.com (v129.4) with ESMTP id MAILINDD031-86094c6a7dff1ac; Tue, 17 Aug 2010 08:18:07 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-da12.r1000.mx.aol.com (Internet Inbound) with ESMTP id 4B20E38000081; Tue, 17 Aug 2010 08:18:06 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1OlL53-0003Zm-VA for rs_out_1@blacksheep.org; Tue, 17 Aug 2010 13:15:49 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1OlL51-0003YQ-K5 for rsgb_lf_group@blacksheep.org; Tue, 17 Aug 2010 13:15:47 +0100 Received: from smtp-out11.han.skanova.net ([195.67.226.200]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1OlL4y-0006UL-Ds for rsgb_lf_group@blacksheep.org; Tue, 17 Aug 2010 13:15:47 +0100 Received: from [127.0.0.1] (81.235.167.68) by smtp-out11.han.skanova.net (8.5.114) (authenticated as u33233109) id 4BC6D1B3028D2B76 for rsgb_lf_group@blacksheep.org; Tue, 17 Aug 2010 14:15:30 +0200 Message-ID: <4C6A7D63.5080106@telia.com> Date: Tue, 17 Aug 2010 14:15:31 +0200 From: "Johan H. Bodin" User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; sv-SE; rv:1.9.1.11) Gecko/20100711 Thunderbird/3.0.6 MIME-Version: 1.0 To: rsgb_lf_group@blacksheep.org References: <002e01cb3dfb$0bd364c0$0301a8c0@your91hoehfy9g> In-Reply-To: <002e01cb3dfb$0bd364c0$0301a8c0@your91hoehfy9g> X-Spam-Score: 1.4 (+) X-Spam-Report: autolearn=disabled,RATWARE_GECKO_BUILD=1.426 Subject: Re: LF: audio amps 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-global-disposition: G x-aol-sid: 3039ac1d40544c6a7dfd6bf2 X-AOL-IP: 193.82.116.20 X-AOL-SPF: domain : blacksheep.org SPF : none X-Mailer: Unknown (No Version) Yes, a DC blocking capacitor is a good idea in some cases. For example, between the audio amp's output and the primary of a matching transformer. Otherwise, a large DC current may flow due to a small DC offset from the amplifier since the winding resistance is close to zero. This is not the case with a loudspeaker which has many ohms of DC resistance. 73 de Johan SM6LKM mal hamilton wrote: > It has been suggested in the past to use a 15 to 20 uF capacitor in > series with the amp output to the antenna, but the transformer method > might be better or use nothing and match the low Z to the antenna. > de mal/g3kev >