X-GM-THRID: 1235289960733538477 X-Gmail-Labels: rsgb lf Delivered-To: daveyxm@gmail.com Received: by 10.35.12.7 with SMTP id p7cs67646pyi; Thu, 3 May 2007 17:24:10 -0700 (PDT) Received: by 10.66.244.10 with SMTP id r10mr2292919ugh.1178238250006; Thu, 03 May 2007 17:24:10 -0700 (PDT) Return-Path: Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mx.google.com with ESMTP id e33si4403864ugd.2007.05.03.17.24.07; Thu, 03 May 2007 17:24:10 -0700 (PDT) Received-SPF: neutral (google.com: 193.82.116.20 is neither permitted nor denied by best guess record for domain of owner-rsgb_lf_group@blacksheep.org) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1HjlXr-0005Tr-Cf for rs_out_1@blacksheep.org; Fri, 04 May 2007 01:21:11 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1HjlXq-0005Ti-UK for rsgb_lf_group@blacksheep.org; Fri, 04 May 2007 01:21:10 +0100 Received: from imo-m12.mx.aol.com ([64.12.136.171] helo=imo-m12.mail.aol.com) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1HjlXp-00076T-S6 for rsgb_lf_group@blacksheep.org; Fri, 04 May 2007 01:21:10 +0100 Received: from WarmSpgs@aol.com by imo-m12.mx.aol.com (mail_out_v38_r9.2.) id l.ca6.f901fac (52354) for ; Thu, 3 May 2007 20:20:55 -0400 (EDT) Received: from FWM-D26 (fwm-d26.webmail.aol.com [205.188.162.2]) by ciaaol-r02.mx.aol.com (v115.11) with ESMTP id MAILCIAAOLR028-cc82463a7c661a4; Thu, 03 May 2007 20:20:54 -0400 References: <004d01c78c3a$48757ec0$0b01a8c0@server> <003501c78c4d$0d68f060$0300a8c0@lark> <006a01c78d17$440b3d60$0b01a8c0@server> <8C95BC9DABC7512-1190-E1D2@FWM-M30.sysops.aol.com> <009101c78dc0$c1836700$0b01a8c0@server> To: rsgb_lf_group@blacksheep.org Date: Thu, 03 May 2007 20:20:54 -0400 In-Reply-To: <009101c78dc0$c1836700$0b01a8c0@server> X-MB-Message-Source: WebUI MIME-Version: 1.0 From: warmspgs@aol.com X-MB-Message-Type: User X-Mailer: AOL WebMail 25698 Received: from 71.50.20.225 by FWM-D26.sysops.aol.com (205.188.162.2) with HTTP (WebMailUI); Thu, 03 May 2007 20:20:54 -0400 Message-Id: <8C95BF936ED4AEE-1BD8-EEA3@FWM-D26.sysops.aol.com> X-AOL-IP: 205.188.162.2 X-Spam-Flag: NO X-Spam-Score: 0.6 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001,NO_REAL_NAME=0.55,UNPARSEABLE_RELAY=0.001 Subject: Re: LF: Re: Passive high-pass filter circuits? Content-Type: multipart/alternative; boundary="--------MB_8C95BF936ED4AEE_1BD8_1BE13_FWM-D26.sysops.aol.com" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.8 required=5.0 tests=HTML_20_30,HTML_MESSAGE, NO_REAL_NAME 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 Status: O X-Status: X-Keywords: X-UID: 1693 ----------MB_8C95BF936ED4AEE_1BD8_1BE13_FWM-D26.sysops.aol.com Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii" > The source and load Z are both 600 ohms. >From your description, the source might be close to that over the range of interest, but can you be sure about the impedance seen by the telco "repeater coil" into the mic input? It will make quite a difference to a simple passive filter. Assuming the figures are reasonably close and the load is mostly resistive in nature, a turnover at 1 kHz and 6 dB down by 250 Hz can easily be exceeded by a single series capacitor (actually two in this case, since it's a balanced line). A .27uF in series with each side of the line will do the trick. If it turns out either impedance is actually lower than you are figuring, you might need a higher value of cap to prevent excess rolloff of lows. And, if either is higher, you might need smaller caps to attain adequate hum suppression. Some experimentation may be needed, in other words. John ________________________________________________________________________ AOL now offers free email to everyone. Find out more about what's free from AOL at AOL.com. ----------MB_8C95BF936ED4AEE_1BD8_1BE13_FWM-D26.sysops.aol.com Content-Transfer-Encoding: 7bit Content-Type: text/html; charset="us-ascii"
> The source and load Z are both 600 ohms.
 
From your description, the source might be close to that over the range of interest, but can you be sure about the impedance seen by the telco "repeater coil" into the mic input?  It will make quite a difference to a simple passive filter.
 
Assuming the figures are reasonably close and the load is mostly resistive in nature, a turnover at 1 kHz and 6 dB down by 250 Hz can easily be exceeded by a single series capacitor (actually two in this case, since it's a balanced line).  A .27uF in series with each side of the line will do the trick.
 
If it turns out either impedance is actually lower than you are figuring, you might need a higher value of cap to prevent excess rolloff of lows.  And, if either is higher, you might need smaller caps to attain adequate hum suppression.  Some experimentation may be needed, in other words.
 
John
 
 
 
 
 
AOL now offers free email to everyone. Find out more about what's free from AOL at AOL.com.
----------MB_8C95BF936ED4AEE_1BD8_1BE13_FWM-D26.sysops.aol.com--