The problem is mismatched impedance. The headphone output of the Discman is 8 to 32 ohms: most of the sound energy is in current, with very low voltage. The MOH input of a phone system is line level - about 600 ohm, so the MOH is expecting a little more voltage. Radio Shack used to and may still sell an 8 ohm to 600 ohm audio transformer, or you could use a 70 volt P.A. transformer with the MOH connected to the 5 watt tap, which is about 600 ohm. (It shouldn't overload the MOH because the Discman output level is nowhere near that of a P.A. amplifier.) One other thing: with this setup, it also helps to put a 100 ohm resistor across the Discman output, in parallel with the transformer.
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Together We Prosper [This message has been edited by Baron-B (edited August 02, 2005).]