There is only one input channel, and the installer had “Y’d” both wireless mics into it.
The output power was too low, and it lacked the proper outputs to drive the auxiliary systems in the facility.
I found a unit in the shop to provide as a substitute. It has two balanced mic level inputs, plus an aux bus and line out.
There is no provision for driving a high impedance loudspeaker system, but one can always add a transformer to get that. I decided to go with it.
Now, interfacing the wireless mics to the mixer/amplifier would seem pretty straight forward, but wait a minute. The inputs are labeled “Low-Z” – not likely in a modern mic input.
A quick check with the ZM-104 showed the input impedance to be about 8 kilohms – a fairly high value for a mic input, and fortunately high enough to not load the wireless receivers.
The impedance is appropriate, but how about the level? The TS-1 revealed that the receiver outputs are pretty hot, probably too hot for a mic level input.
Also, the inputs on the mixer/amplifier are balanced XL, which opens the possibility of the presence of phantom power. A line level unbalanced output to a mic level input with the potential of phantom power? It’s not looking good.
Since it is not a good idea to send phantom power to an entry level unbalanced receiver, I thought that I had better check. The TS-1 delivered a significant “click” when connected between pin 1 and each of the other pins on the mixer’s input XL connector. This indicates the presence of DC.
A quick test with a volt-ohmmeter revealed 24 volts DC phantom power (with no labeling on the input to indicate its presence). I determined that the inputs were mic level by using the handset as a mic by connecting it across pins 2 and 3.
A simple “Check 1,2” produced plenty of level, so the input had to be mic level. This was not going to be a simple “adapt-the-jack” interface job, but it is a made-to-order situation for a transformer.
I had a couple of small ones in the shop that I hoped would work. What I really needed was a “step-down” transformer to drop the output voltage of the receiver and block the phantom power from reaching it.
The units that I had were labeled as being “bridging” transformers, which leaves room for doubt regarding what they are actually doing. After all, a 1:1 transformer would present a high (bridg-ing) impedance to an output if its sec-ondary is connected to a high impedance input.
There’s no need to guess, since the tools in Case A could quickly determine the turns ratio of these units.
The 3:1 transformer turns ratio would be adequate for dropping the receiver output voltage to drive the mic level inputs. I installed the transformers and set the mixer input levels to their mid (12 o’clock) setting.
A quick listen with the handset at the mixer/amplifier’s output revealed that things were loud and clear.
On To The Output
It was now time to address how to drive the ceiling loudspeakers.