Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/5/84; site angband.UUCP Path: utzoo!watmath!clyde!burl!ulysses!allegra!bellcore!decvax!genrad!teddy!panda!talcott!harvard!seismo!ut-sally!mordor!angband!sjc From: sjc@angband.UUCP (Steve Correll) Newsgroups: net.audio Subject: Re: Adding a buffer amp Message-ID: <38@angband.UUCP> Date: Fri, 11-Jan-85 13:34:08 EST Article-I.D.: angband.38 Posted: Fri Jan 11 13:34:08 1985 Date-Received: Sun, 13-Jan-85 08:11:12 EST Distribution: net Organization: S-1 Project, LLNL Lines: 29 If 10k ohm output impedance is typical, I guess the audiophile agitation about cables may have a technical foundation. A few years back, IHF added to its preamp-testing standard a test-load designed to weed out products with high output impedances; apparently many manufacturers are ignoring it. At any rate, one article about putting a buffer between a preamp output and your cables appears in issue 4 of the 1977 Audio Amateur magazine. Unfortunately, you must buy the entire year of 4 back issues for $10 (Box 176, Peterborough, NH 03458, USA). The same people, wearing a different hat, also sell for $17.50 a kit KH-8 called the "Morrey Super Buffer", including parts and board, but not the instructions, which appear only in the original magazine article (Old Colony Kits, Box 243, Peterborough, NH 03458; VISA, MC 603 924-6526). That's kind of expensive for such a simple circuit, particularly if you want to make several copies of it; an alternative would be to get the National Semiconductor Audio/Radio Handbook (About $6 from National Semiconductor, 2900 Semiconductor Drive, Santa Clara, CA 95051 (408) 737-5000), and hunt up your own parts. In addition to discussing RIAA preamps, tone controls, graphic equalizers, mixers, etc. this book has one appendix on power supply design and another appendix with basic op-amp configurations and the equations pertaining to them. Section 2.19 of the 1980 edition talks about driving low-impedance lines, but it's wild overkill; a simple non-inverting buffer (circuit A4.4 on page 6-12 of my edition) ought to suffice. Enjoy. -- --Steve Correll sjc@s1-c.ARPA, ...!decvax!decwrl!mordor!sjc, or ...!ucbvax!dual!mordor!sjc