Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83 v7 ucbtopaz-1.8; site ucbtopaz.CC.Berkeley.ARPA Path: utzoo!watmath!clyde!burl!mgnetp!ihnp4!zehntel!dual!amd!decwrl!decvax!ucbvax!ucbtopaz!newton2 From: newton2@ucbtopaz.CC.Berkeley.ARPA Newsgroups: net.audio Subject: Re: Re: Wiring Your House for Sound (pt 2 of 2) Message-ID: <520@ucbtopaz.CC.Berkeley.ARPA> Date: Fri, 10-Aug-84 01:26:40 EDT Article-I.D.: ucbtopaz.520 Posted: Fri Aug 10 01:26:40 1984 Date-Received: Sun, 5-Aug-84 05:49:21 EDT References: <90@whuxl.UUCP>, <522@clyde.UUCP> Organization: Univ. of Calif., Berkeley CA USA Lines: 53 I agree (since I was one of those who proposed it) that the most sensible solution is to run low-level audio everywhere and have locally sited power amps drive nearby speakers. HOWEVER, well-intentioned mythology isn't limited to insisting on stranded bus-bars (bifilar niobium-tin braid, helium-cooled?). While so-called low-impedance lines (low source impedance, that is) are a necessity, this is largely to avoid high-frequency roll-off due to the shunt capacitance of long lines. For interference rejection, low impedance is most resisant to capacitively-coupled crosstalk. Balanced lines, however, are usually overkill, although an indispensible marketing ploy, particularly in semi-pro gear- likewise the use of "Cannon" or XLR-type connectors. Believe me, no one needs or will long tolerate XLRs at home- they seem neat when you're a hobbyist pretending to be Captain Video, but if you really are a professional audio drudge and have a living room cluttered with that fabled "professional" gear, it gets old fast. By and large, consumer stuff is as good or better *in performance* as just about any commercial or recording studio stuff- the difference is in ruggedness, serviceability, conformance to interface standards and other costly features you can't hear. And consider how one would distribute "balanced" audio: unless you resort to transformers, which are *VERY* expensive at the quality levels which bear mentioning on net.audio, you will have to set up some variety of kludged differential input at each amp, and will also consider how to derive an allegedly "balanced" *output* to drive the line. I say allegedly because the concept of "balanced" is ill-defined (or underdetermined) in audio parlance- sometimes one means "floating", i.e. both signal conductors exhibit a high impedance to ground; sometimes "balanced to ground", meaning equal but not large impedances to ground. Sometimes the source is single-ended but the load is differential, and so endlessly on. Each configuration has its applications in interference-rejection or particular measurement applications (consider the power-amp as measuring the signal-plus-noise presnted to it and trying to derive the best estimate of the signal alone). In most domestic installations, low source- impedance single-ended circuits will prove adequately immune (if shielded!) to *induced* noise; the more likely source of problems is from ground-loop hum, and possibly RFI. As much thought will be necessary to eliminate this with all but the floating transformer-to-floating transformer setup regardless of whether single-ended or differential circuits are used. I'm not disparaging differential approaches, just trying to keep effort/benefit ratios in perspective. The first thing to try is lifting the AC power grounds of one or more units of widely dispersed systems. By the way, I don't know what to make of the prescription "common mode rejection should be 100 dB or more". Is this like saying everyone should be healthy, wealthy and wise? Just the twisted-pair *cable* is likely to have worse than 100 dB CMRR over DC-20 kHz, and that's only a tiny slice of the spectrum of interest to *real* audiophiles, eh?