Path: utzoo!attcan!telly!problem!compus!lethe!yunexus!ists!helios.physics.utoronto.ca!news-server.csri.toronto.edu!bonnie.concordia.ca!nstn.ns.ca!news.cs.indiana.edu!att!linac!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!casbah.acns.nwu.edu!nucsrl!telecom-request From: jeh@dcs.simpact.com (Jamie Hanrahan) Newsgroups: comp.dcom.telecom Subject: Re: How do You Hook up a Phone For a Play? Message-ID: Date: 22 Feb 91 22:44:07 GMT Sender: news@casbah.acns.nwu.edu Organization: Simpact Associates, San Diego CA Lines: 37 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 151, Message 8 of 8 Originator: telecom@delta.eecs.nwu.edu In article , Barton.Bruce@camb.com (Barton F. Bruce) writes: > [you really need to be close to 20 or 30 Hz to do this right] How about: Connect an audio function generator to a line-level input on a reasonably-powered (say 30 W) audio amp. Connect speaker-level output of amp to the 8-ohm side of a 70-volt-to-8-ohm transformer, such as is used in PA systems. Connect 70-volt side of transformer to phone. Or, try any audio output transformer you happen to have lying around. You will have to experiment a bit with the gain on the amp to get the right voltage into the phone. (As always, start low and work up, not the other way around!) Using an audio amp and a function generator is an old laboratory trick for getting variable-frequency power, rather than just waveforms, at voltages and currents much higher than any function generator can provide. Typically it's used when you want something approximating an AC power supply (=> low source impedance) so a good transistor amp with high power and a very high speaker damping factor (50:1 is good) is used, with no output transformer. An old favorite (mostly because it seems to be indestructible) is the Crown DC-300A, so named because of its flat freq response at full- power from (near) DC to 300 KHz. If you don't have one of those, any brute-force amp with a hefty transformer and lots of output transistors should do. (Don't try this with Carver or other amps with trick power supplies) Jamie Hanrahan, Simpact Associates, San Diego CA Internet: jeh@dcs.simpact.com, or if that fails, jeh@crash.cts.com Uucp: ...{crash,scubed,decwrl}!simpact!jeh