BRUCE@ccavax.camb.com (Barton F. Bruce) (10/29/90)
In article <14092@accuvax.nwu.edu>, Andy Jacobson <IZZYAS1@oac.ucla. edu> writes: > Would it be possible to simply put a high Z or > xformer isolated source across it and create your own music on hold > circuit? You should use transformer isolation, and that is exactly what the ITT K-403A music-on-hold card did. It had to be plugged into a k259 panel (that gave you wrap tails to use as needed, rather than be prewired for normal card use). There probably is a FAT cap in there to block DC fron the xfmr's secondary. There is 1 input xfmr, and 6 output ones on the k-403 card. One normally used it with the k-400E cards that had a jumper option to put pin 18 to the RING side of the resistor (was 120 ohms on those cards). That side was the one that got switched. The TIP end of the resistor was directly connected to TIP, so the MOH xfmr was connected from pin 14 to pin 18. Any wire to pin 18 (and 3) was normally for A battery for 401 manual intercoms or 415s or anything needing quiet 'TALK BATTERY'. If these were multipled or even connected to A battery and ground, the existing wires have to be removed first. In the case the 501 KSUs, 18 and 3 were brought out and punched down seperately for each card slot so there was no problem. On some of the really newer KSUs that used 20 pin connectors, 18, 3, 0, 19 were ALL brought out seperately for whatever options needed them. Rather than muck with the KSU, you could instead tack solder a pair of wires to the ends of the resistor, and bring the wire out to a cheap connector or something similar for easy servicing. If you get a k403, here are the connections. Jumper ABC is for input impedance. For 500 ohm in, jumper plugs BC, for 8000 ohm, use AB. output pins for 6 ckts: 1,2/3,4/5,6/13,14/15,16/17,18 input pair pins 7,8 power (filtered A battery) 9=A-bat, 11=A-gnd It is designed to have at least 45 db isolation between any two lines connected and getting 'music' (or quiet). Someone else once made such a unit with one output xfmr with several windings. I assume and crostalk isolation was done with pads after the xfmr.