Scott McDonnell wrote:

Hello,

My father owns a few resturaunts and these use 70V commercial sound
systems for the background music. In one of his stores, the speakers
are making a crackling or popping sound all of a sudden. He asked me
to change 3 speakers (they were in quiet areas where it was most
noticeable so he thought that was all it was) and the problem is
still there, even in the new speakers. I started suspecting the 70V
amplifier. He had a spare one, though it was used and about as old,
so I installed that one to see if there was a difference. The
crackling was still present. Anyone have any ideas what to check
for?

So far, I have tried:
replacing a few speakers
tried a different, but not new, 70V amplifier
tried different wattage settings at the speakers
tried to adjust the volumes on both amp and source
balanced bass and treble

None of this seems to work. I do have an oscilloscope
and know how to use it, but have not had a chance to
bring that with me and look at the signals. Any suggestions?

Scott

First, what brand and model of unit are you using?
And i hope your not going to say radio shack.
It pays to get a high quality commercial unit.

The total number of all the taps must not exceed the amplifiers rated
outputs. Many non knowing people hang a 8 ohm speaker on to a 70 volt
line and wonder why the system went to hell. You can measure this system
load at the amp, but you need an impedance meter. A DVM will NOT do
this. Something like a TOA ZM 104 will. How many speakers?
what are there taps? do they ALL have line transformers on them?

Now, i have run into a situation like yours with a satellite receiver.
There was a grounding issue between the two units. The units needed
transformerisolation between them to float the audio grounds to solve
the problem.

Bob


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