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#607340 - 01/22/17 10:55 PM Re: co port paging voltage [Re: hbiss]  
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Originally Posted By: hbiss
Ask an IT wienie how to connect to a paging system and see what answers you get.

-Hal


Well, I'm kinda of an IT weenie and I can do most paging hooks ups.

Last edited by Mercenary Roadie; 01/22/17 10:56 PM.

Patrick T. Caezza
Santa Paula, CA 93060
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#607404 - 01/25/17 05:52 PM Re: co port paging voltage [Re: davetel]  
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Hal,

I respect your comments and opinions, however, I stand by my original comments.

To prove the point, I sent a 1 KHz sine wave audio signal through a telephone and connected an oscilloscope to the phone system paging port. The level was -10 db. The trace was clean of distortion.

I connected the telephone system paging port to a Bogen TPU-100 telephone input port. The scope view showed about a .05% distortion that was added. I looked at the output of the Bogen and, as expected, the amplitude was clean except for the small distortion noted at the input.

I took the same telephone system output and connected it to the Bogen AUX input. There was about a .1% distortion added by that input. The amplified output had a 10% distortion in it. It was audibly noticeable. I inserted a WMT-1 between the telephone system input and the AUX on the amplifier. There was no distortion at the input. The amplifier output was clean and only registered a .05% distortion. This was not audibly noticeable.

I took that same telephone system output and connected it to a mic input. With no transformer, the sine wave was greatly distorted at the input and the output did not resemble a sine wave. Even limiting the input level to -60 db, the sine wave was noticeably distorted. Using a mic to line level transformer, which matched the 600 ohm telephone system output to the balanced 150 ohm mic input produced a clean sine wave with about .01% distortion. The distortion increased as the level increased, however, within the normal paging range, the distortion was not noticeable.

When I install a telephone system to a paging amplifier, unless the amplifier has a "telephone input" of 600 ohms, I ALWAYS use a matching transformer. My hearing isn't what it used to be, the "Scope don't lie."

Rcaman


Americom, Inc.
Where The Art And Science Of Communications Meet
#607411 - 01/25/17 08:05 PM Re: co port paging voltage [Re: davetel]  
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Facts don't lie, and my only argument is as I stated above: phone systems aren't audio gear. Phone lines should be balanced 600 ohms and if the designer made the page port the same as a station port then you may or may not need a balun, depending on how he did it. I think your tests prove that with that particular system the WMT1 is needed, but there are others that won't. Read the manual and see what it says. In this case there is definitely something about the connection to the amp that the page port doesn't like. Should you always use a WMT1? If you know what you are doing and can understand what's going on like Ralph does I certainly would carry one in my truck. Try it without first and if that's no good see if the WMT1 makes it better. But either way make sure you know how to connect to the amplifier first so that an improper connection or input isn't really to blame.

-Hal


CALIFORNIA PROPOSITION 65 WARNING: Some comments made by me are known to the State of California to cause irreversible brain damage and serious mental disorders leading to confinement.
#607418 - 01/26/17 05:38 AM Re: co port paging voltage [Re: davetel]  
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Thinking some more about this, my experience is mainly with Partner and any paging I provided with it was almost always through a Bogen TPU amp. I always used the 600 ohm paging input for no other reason than it was there and provided ducking of the music on page. I do however remember using a PA amp in one installation and with that I went directly into an aux input from the Partner page port with absolutely no problem. The page output on the ACS is 600 ohms according to the manual.

I also did many Panasonic KX-T61610 systems before Partner. As I remember they had an RCA jack for the page output that I connected directly to a PA aux input with a shielded audio cable. It too was 600 ohms according to the manual.

So this kind of problem seems to be very much dependent on the system manufacture and from my experience of having no problems is surprising to me.

-Hal

#607420 - 01/26/17 03:56 PM Re: co port paging voltage [Re: davetel]  
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I go back a little. Back when I was installing crossbar PBX, the page port was always a station port of 900 ohms. The amplifiers were all tube type and, fresh out of the box, they had 5-10% distortion. They usually had one "input" and it was between 10K and 15K ohms. A matching transformer had to be used, no exceptions.

With the advent of electronic systems, Key and PBX, the output is usually provided to match a 600 ohm amplifier input. Some dinky systems have an 8 ohm output and they, usually, require a matching transformer.

We have paging systems in chemical plants and coal mine offices. The voice quality has to be absolutely clear as specific emergency instructions are announced via PA system when an emergency occurs. They will not tolerate ANY distortion, so it has been a pet project of mine to make sure everything matches and the distortion is kept as low as possible. That is why we have Tektronix scopes, distortion meters and spectrum analyzers. That is why I am obsessive about matching impedance parameters. Hal is correct in stating the situation is system specific. As he suggested, hook it up and if it sounds good, walk away. If you have hum and/or distortion, find the correct matching transformer that will resolve the issue and ALWAYS keep the level below overload which is the primary cause of distortion in most PA systems.

Rcaman


Americom, Inc.
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#607421 - 01/26/17 05:35 PM Re: co port paging voltage [Re: davetel]  
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Ralph, I assume you did this test on an ESI KSU. I find it interesting that, with the scope still connected to the page out, as soon as you connect it to the amp you see waveform distortion. I would think that even .05% occurring when connected to a 600 ohm input is indicative of poor design. Just for giggles did you ever try putting various resistive loads on the page output while looking at the waveform? Starting with maybe less than 600 and working up to 10k to see what happens?

-Hal


CALIFORNIA PROPOSITION 65 WARNING: Some comments made by me are known to the State of California to cause irreversible brain damage and serious mental disorders leading to confinement.
#607444 - 01/27/17 03:01 PM Re: co port paging voltage [Re: davetel]  
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Hal,

I expect to always see some distortion added unless the input pre-amp circuits of the amplifier are exactly matched. It does occur, but not as often as I would like. This circuit unbalance is the cause of the distortion. I have run these tests on Mitel, ESI, Comdial and X-Blue systems and the results are close.

As an exercise in futility, I took the pre-amp ICs of an out of the box Bogen that was adding a bit of distortion. I matched two input pre-amp ICs and changed one feedback loop resistor and I was able to achieve less than .001% added distortion. That's about the limit of my equipment, and, at that percentage, it is not audible.

I did play around with matching transformers and impedance. Adding resistors and matching the balance of baluns will, occasionally, improve performance. However, you made the statement: "poor design" is the normal with telephone system paging circuits which, more often than not, nothing more than a cheap transformer and, occasionally, in a real stroke of genius, a real matching circuit that delivers an actual 600 ohm impedance.

I count it a win when the output is clean and without noticeable distortion.

Rcaman


Americom, Inc.
Where The Art And Science Of Communications Meet
#608223 - 02/24/17 07:28 AM Re: co port paging voltage [Re: davetel]  
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Yes, you’ll are right. In America and North America we use 600 ohms.

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