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#607016 01/14/17 04:22 PM
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davetel Offline OP
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my customer bought an xblue from amazon. they didnt know it didnt have a paging port. xblue tells me i can use a co line port with our existing bogen amp if i give it 24vdc in parallel. does the transformer go in ahead of the amp or behind the amp. thanks, dave.

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I highly recommend that you obtain a Viking Electronics FXI-1 Paging port to CO Line interface.

From the way you asked the question, I would hesitate to try and describe how to PROPERLY design a simple circuit to provide the DC talk voltage while maintaining the proper impedance of 600 ohms for the CO trunk port.

Please don't think I am talking down to you, but you should not try and just "parallel" on DC talk voltage and expect things to work.

The FXI-1 will resolve all your problems in a nice, neat unit priced at under $100.

Rcaman

Last edited by Rcaman; 01/15/17 04:54 PM. Reason: Impedance Mistake

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yes save yourself a lot of grief, this requires a filtered battery not just 24vdc


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Isn't the c.o. port 600 ohms?


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Yep, John, you are correct. CO trunk ports in the United States and North America are 600 Ohms real. In the rest of the world, they are 900 Ohms complex.

The point is the Viking Electronics unit will match and provide the filtered talk voltage needed for this situation.

Rcaman


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I've never used that unit so I guess it's switchable 600 or 900 to match?
Thanks


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I guess it's switchable 600 or 900 to match?

Doesn't have to match. If you want to know more look HERE and click on the manual link to read the manual.

-Hal


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Looks to me that it is a 600 ohm matching device. Says so twice in the spec.'s my guess is it is for US and North American applications.


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Impedance matching really is an issue when your source is 600 or 900 ohms and your amplifier is 10K Ohms. The matching is done to reduce hum and get the signal as close to intelligible as possible.

Since the OP is using a Bogen amp, it is likely there is a Telephone paging port that would match.

Rcaman


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Impedance matching really is an issue when your source is 600 or 900 ohms and your amplifier is 10K Ohms. The matching is done to reduce hum and get the signal as close to intelligible as possible.

I disagree. Gone are the days when we matched the source impedance to the load. Today it's a low impedance into a high impedance and that's both for an unbalanced and balanced line. It matters little what the source impedance is as long as it's lower than the load, all that matters is that it is at a suitable level that the particular amp input wants to see.

BUT for long balanced lines it is best to use transformers at each end that will provide good balance and an impedance match to each other. Then, yes, you do that to minimize or eliminate hum pickup and other common mode noise.

The 600 ohm impedance is for audio out of the FXI that gets connected to the paging amp input which is generally something like 10k. Nothing to do with the phone line.

-Hal



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