Return-Path: Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-mp06.r1000.mx.aol.com (Internet Inbound) with ESMTP id 74CE43800015B; Fri, 16 Dec 2011 13:56:03 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Rbcvg-0005i9-0V for rs_out_1@blacksheep.org; Fri, 16 Dec 2011 18:54:48 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Rbcvf-0005i0-HG for rsgb_lf_group@blacksheep.org; Fri, 16 Dec 2011 18:54:47 +0000 Received: from mail-gy0-f171.google.com ([209.85.160.171]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1Rbcvd-00046y-FB for rsgb_lf_group@blacksheep.org; Fri, 16 Dec 2011 18:54:47 +0000 Received: by ghy10 with SMTP id 10so2186271ghy.16 for ; Fri, 16 Dec 2011 10:54:38 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type:content-transfer-encoding; bh=Kpe5sBFOdSyXH5y9LlJEuOioDVFyV2OIYumfO3Esy5o=; b=uKX5fHixfuCLSAeJ9SIUKWJkX5bk9FZhEHV1Vjsd15Y/QbLw3GAl0kGG45pcvYRVF5 sKiafhr77khuH8PXefVxQt7UH7VCszvHHMsP06wmq0FRrnkAOFdsgie0bJu4cuKZVeGD b9tA+53hDakeJmAgYBMplGP50H4jIF2Cpqgg8= MIME-Version: 1.0 Received: by 10.50.236.40 with SMTP id ur8mr9873072igc.91.1324061678349; Fri, 16 Dec 2011 10:54:38 -0800 (PST) Received: by 10.231.66.5 with HTTP; Fri, 16 Dec 2011 10:54:38 -0800 (PST) In-Reply-To: <9147461.1324046122200.JavaMail.root@wamui-bucket.atl.sa.earthlink.net> References: <9147461.1324046122200.JavaMail.root@wamui-bucket.atl.sa.earthlink.net> Date: Fri, 16 Dec 2011 18:54:38 +0000 Message-ID: From: Andy Talbot To: rsgb_lf_group@blacksheep.org X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,none Subject: Re: LF: RE: Wellbrook Loop Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable 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-SCOLL-SCORE: 0:2:419197632:93952408 X-AOL-SCOLL-URL_COUNT: 0 X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-d231.2 ; domain : gmail.com DKIM : pass x-aol-sid: 3039ac1dc14a4eeb9443173e X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none A very interesting circuit concept - I hadn't heard the term "augmentation" before. (It looks to have something in common - and completely turned upside down - with the bootstrapping technique used to increase the input resistance of emitter follower stages) But, looking at the circuit of the preamp in Figure 6, I'm wondering if, instead of what is virtually two independent input stages, with their own separate transformers, you considered a differential push-pull feedback as a single entity. Have a centre tapped secondary in the bases (with the centre tap to AC ground), but with the primary connected between the two emitters, ie directly across the loop input. The two input transistors now operate in true differential mode, rather than as mostly-independent amplifier stages, and with only one feedback transformer, complexity and wire losses are reduced. This will give even more decoupling of the loop from ground. Andy www.g4jnt.com On 16 December 2011 14:35, Chris Trask wrote: >> >> This one from Chris has an input stage similar to the design >> I did those years ago, but with added feedback and more. >> The common base push-pull running open-loop, if memory serves, >> gave about 0.5 ohms input impedance running the devices at >> 100mA (on heat sinks !) >> > > =A0 =A0 Using the augmentation gives you a similar input impedance at far= less current. =A0It gives you the opportunity to operate the transistor at= it's best NF. > > Chris > > >