Return-Path: Received: from mtain-di02.r1000.mx.aol.com (mtain-di02.r1000.mx.aol.com [172.29.64.6]) by air-dc05.mail.aol.com (v129.4) with ESMTP id MAILINDC054-86a34d0a8f24283; Thu, 16 Dec 2010 17:13:56 -0500 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-di02.r1000.mx.aol.com (Internet Inbound) with ESMTP id AEABB380000BA; Thu, 16 Dec 2010 17:13:54 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1PTM4X-0002JX-9A for rs_out_1@blacksheep.org; Thu, 16 Dec 2010 22:13:13 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1PTM4W-0002JO-OP for rsgb_lf_group@blacksheep.org; Thu, 16 Dec 2010 22:13:12 +0000 Received: from mail-iy0-f171.google.com ([209.85.210.171]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1PTM4U-0000CD-69 for rsgb_lf_group@blacksheep.org; Thu, 16 Dec 2010 22:13:12 +0000 Received: by iyj21 with SMTP id 21so9521iyj.16 for ; Thu, 16 Dec 2010 14:13:03 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:received:in-reply-to :references:date:message-id:subject:from:to:content-type; bh=JkwhI7XvhJ8YDRmLPkftspW/lSKXeqFHVddxIUxDJ4g=; b=mxMHjZUcG+ZoZGK+mAfIi1pJBO44gAWoVAQxKdVyDt4m3Ngp/jVDJvJeWgEh8mkyF5 viIpWAbXMJaqGb+ohiN3oQsX2YQTz/p6EMuzT3KX2i8fI803/G5U+ynECF4mVw1wvJJ1 yBi0C2QiEs4YZz9U29B3DTWs2M5pKVYMVp2bk= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=tQiIlRaJ8IpALo3HptqyF+aX0Qg4ykGe4pw+f6FFHCzscGeqFkPyENWvWn2LLZq0eo XTLPHdxJrAPbfaiKBycUpdHAazK37YMm0vjGLuEcfoqmVtKRMQofXCOYCjUBy6mALWsT nRoDxq+Q1i16P962YUMktWgd9qPlGuKHF5RZM= MIME-Version: 1.0 Received: by 10.231.35.131 with SMTP id p3mr44515ibd.87.1292537583178; Thu, 16 Dec 2010 14:13:03 -0800 (PST) Received: by 10.231.200.211 with HTTP; Thu, 16 Dec 2010 14:13:03 -0800 (PST) In-Reply-To: References: Date: Thu, 16 Dec 2010 22:13:03 +0000 Message-ID: From: Andy Talbot To: rsgb_lf_group@blacksheep.org DomainKey-Status: good (testing) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: Re: LF: Sound Card mic Impedance Content-Type: multipart/alternative; boundary=00032557a2ba811bd604978e5b01 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.6 required=5.0 tests=HTML_20_30, HTML_FONTCOLOR_UNSAFE,HTML_MESSAGE 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-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-m217.2 ; domain : gmail.com DKIM : pass x-aol-sid: 3039ac1d40064d0a8f2206e4 X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none X-Mailer: Unknown (No Version) --00032557a2ba811bd604978e5b01 Content-Type: text/plain; charset=ISO-8859-1 Have just being playing with AADE, to try to see why it pretends to be able to do low pass filters with unequal impedances. All it appears to do is choose a set of values that maintains the specified passband response when terminated with the specified Rin/Rout values - it does not actually attempt to match them so there is an actual resistive power loss in such unequal terminated filters. Which all seems totally and utterly pointless. Might just as well slug one of the unequal impedances with an auxilliary R to make them equal, then design an equally terminated filter. Andy www.g4jnt.com On 16 December 2010 20:58, Andy Talbot wrote: > Very good point... > of course it can't... > - just saw the option in the design S/W and didn't actually try it out. > > OOPs !!!!!!! > > I've done this quite often with bandpass filters, where it does work very > well indeed, and can sometimes be used to improve the shape over an equally > terminated design. Particularly for top coupled designs > > Andy > > > > > On 16 December 2010 20:49, James Moritz wrote: > >> Dear Andy, LF Group, >> >> Unfortunately, this doesn't quite work... If you think about it, at very >> low frequencies, any low-pass filter will just be a "straight through" >> connection, so in your example will just give whatever voltage the 50ohm >> source delivers to a 500ohm load with no filter present. The filter >> synthesis algorithm then makes a circuit that extends a more-or less flat >> response at this level up to somewhere near the cut-off frequency. You >> could, however, design a "peaked low-pass" circuit that would give voltage >> gain over a relatively narrow frequency range just below the cut-off >> frequency, falling to unity at DC - a pi matching network does this, for >> example. >> >> Cheers, Jim Moritz >> 73 de M0BMU >> >> ----- Original Message ----- From: "Andy Talbot" >> To: >> Sent: Thursday, December 16, 2010 8:25 PM >> Subject: Re: LF: Sound Card mic Impedance >> >> >> >> If its a passive L/C filter, why not do a version with unequal Zin and >>> Zout >>> and take advantage of the voltage gain in going from 50ohms to, say, 500 >>> ohms? That will give you an apparant 10dB without trying. >>> >>> >> >> > --00032557a2ba811bd604978e5b01 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
Have just being playing with AADE, to try to see why it pretends to= be able to do low pass filters with unequal impedances.
=A0
All it appears to do is choose a set of values that maintains the spe= cified=A0passband response when terminated with the specified Rin/Rout=A0v= alues - it does not actually attempt to match them so there is an actual= resistive=A0power loss in such unequal terminated filters.=A0=A0
=A0
Which all seems=A0totally and utterly pointless.=A0=A0 Might just as= well slug=A0one of=A0the unequal=A0impedances with an auxilliary R to mak= e them equal, then design an equally terminated filter.
=A0
Andy
=A0


=A0
On 16 December 2010 20:58, Andy Talbot <andy.g4jnt@gmail.com= > wrote:
Very good point...
of course it can't...
=A0- just saw the option in the design S/W and didn't actually tr= y it out.
=A0
OOPs !!!!!!!
=A0
I've done this quite often with bandpass filters, where it does= work very well indeed, and can sometimes be used to improve the shape ove= r an equally terminated design.=A0=A0 Particularly for top coupled designs=
=A0
Andy
=A0


=A0
On 16 December 2010 20:49, James Moritz <james.moritz@btopenworld.com> wrote:
Dear Andy, LF Group,

Un= fortunately, this doesn't quite work... If you think about it, at very= low frequencies, any low-pass filter will just be a "straight throug= h" connection, so in your example will just give whatever voltage the= 50ohm source delivers to a 500ohm load with no filter present. The filter= synthesis algorithm then makes a circuit that extends a more-or less flat= response at this level up to somewhere near the cut-off frequency. You co= uld, however, design a "peaked low-pass" circuit that would give= voltage gain over a relatively narrow frequency range just below the cut-= off frequency, falling to unity at DC - a pi matching network does this,= for example.

Cheers, Jim Moritz
73 de M0BMU

----- Original Message -----= From: "Andy Talbot" <andy.g4jnt@gmail.com>
To: <rsgb_lf_group@blackshee= p.org>
Sent: Thursday, December 16, 2010 8:25 PM
Subject: Re: LF: Sound Card= mic Impedance=20



If its a passive L/C filter,= why not do a version with unequal Zin and Zout
and take advantage of= the voltage gain in going from 50ohms to, say, 500
ohms? =A0 That will give you an apparant 10dB without trying.





--00032557a2ba811bd604978e5b01--