Anatomy of a Service Call

Even the most basic sound reinforcement systems can have problems.  The system at a chapel in a local retirement home is one of them. Distortion, poor gain before feedback and intermittent operation can be some of the troubles. 2 lavs that distort easily are the first offenders.  Although easily replaced by 2 wired mics there are no mic jacks and the owners do not want any visible cables. In determining possible solutions it is best to start at the input and work your way to the output of a system. First were the wireless mic connections. A balanced TRS output was present but a test with the TS-1 handset proved there was signal only on the tip , making it an unbalanced connection.  The mics sounded ok so they were ruled out as the source of distortion. The amplifier present was not appropriate for the application. It was low on power and had only 1 input channel that the installer summed both mics to. It also lacked the proper outputs to feed the auxiliary systems in the facility. The unit used to replace it had two balanced mic level inputs, an aux bus, and a line out.  Problems interfacing the receiver with the amp/mixer arose when the inputs were found to be labeled “low Z”. A quick check revealed the impedance was appropriate at 8kΩ but the level was unknown and presence of phantom power was suspected which was not good. This was the perfect situation for a step down transformer. One that would step down the output voltage of the receiver and would also block the DC voltage from the phantom power. The next factor down the line was the ceiling loudspeakers. Tests revealed high resistance coming from the loudspeakers, in a typical situation a high voltage amp output would be needed but this being a place where a lower level than usual is required the amp would be fine. It worked, the loudspeaker system provided adequate level while limiting when a speaker spoke too loud.  Driving the balanced input of the hearing assist systems also proved the system was functioning properly. A quick look at the wiring diagram showed it to be wired for a low voltage amp but being driven by a high voltage amp. The distortion created by that setup rendered the system useless. Lastly was the wireless mic reception.  1 of them worked fine across the whole area but the other had a few dropouts. The receivers lived in an adjacent room which blocked signal and with no other way to wire them in the main room the only solution was to leave the door open during service. These all proved simple and easy solutions to entry level systems. The perfect solution to many of these problems was to begin with adequate equipment. Consumers often go with low budget systems which later haunt them with problems.

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