Path: utzoo!mnetor!uunet!husc6!mailrus!nrl-cmf!ames!pasteur!trinity!max From: max@trinity.uucp (Max Hauser) Newsgroups: sci.electronics Subject: Re: E-Bow (how it works) Message-ID: <1567@pasteur.Berkeley.Edu> Date: 15 Mar 88 20:17:10 GMT References: <1752@c3pe.UUCP> Sender: news@pasteur.Berkeley.Edu Reply-To: max@trinity.UUCP (Max Hauser) Organization: UC Berkeley Lines: 32 Summary: negative resistance In article <1752@c3pe.UUCP> maugorn@c3pe.UUCP (Steve "Maugorn" Haug) writes: > >... Is this thing JUST a battery powered electromagnet? Or is >it, as I suspect, an oscillator hooked up to the current going through the >electromagnet? What frequency(ies) of oscillation might we be talking about? >I have made this effect by holding a small speaker with the output of the >guitar coming out of it up to the pickups. This is easy, the guitar will >feed back and resonate on it's own peaks and the frequencies to which the >strings are tuned/fretted. How does this thing induce resonance without >being dependent on the output or knowing how your guitar is tuned or what >note you are about to play? Very easily, presumably; the same way that variable-frequency oscillators work without knowing in advance what tuned circuit will be connected to them. Negative resistance: you need only overcome the built-in loss in the resonant element (be it LC circuit, crystal, or guitar string) in order to get it oscillating steadily. Indeed, Steve was doing this too in a roundabout way with the feedback configuration, although the coupling there may have been acoustic rather than electromagnetic. But it's no big deal to build a circuit with a pair of electrodes that will oscillate when any of a wide range of resonant devices is connected across the pair (I've done it countless times, and not always deliberately); doing the same thing with magnetic coupling would be only slightly more complicated. After all, if the resonant string is magnetically active and placed near a coil, it will induce a resonant component in the coil's impedance, just as it would induce a resonant component in the impedance of an acoustic transducer as well. As Jack Palance says, "Believe it -- or not!" Max Hauser / max@eros.berkeley.edu / ...{!decvax}!ucbvax!eros!max