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
