I understand that a 70-volt transformer is used in a commercial environment, to connect several 70-volt speakers to a 70-volt amplifier. But why does a 70-volt transformer have all of those different colored wires coming from it? What do they connect to, and what are they for? How would I connect a 70-volt transformer to an amplifier, and where I connect the cable that goes to the speakers? Please explain this to me in an easy to understand way, because I was curious about this for a long time.
Briefly, the reason for the multiple wires is so that a given transformer provides the option to select any of a variety of output watts, depending on its application. In other words, instead of a system installer having 1/2W transformers for classrooms, 1/16W transformers for tiny study rooms, and 2W transformers for hallway speakers, they use mostly ONE type of transformer for the majority of the installation, and select appropriate “tap” settings for each speaker's application. These selection possibilities may or may not be marked on the transformer, however! I used to use transformers that had center-tapped dual primaries that could be connected either in various series or parallel combinations, providing a whole range of wattage possibilities. This was done by looking at the spec. sheet and using any of 8 or so different wattage hook-ups by interconnecting the appropriately colored wires. Not all were used, depending on the desired wattage. There were NO markings on the transformer itself, other than the part number! I don't know your situation (or your transformer), but in general: The 70-volt line output covers the distance to the transformer-plus-speaker location, the transformer wire taps are selected for the desired output wattage to the selected speaker, and the sum of all the speaker wattages must be less than that of the amplifier rating. However, knowing the matching transformer's capability and wattage selection scheme is a key element. With luck, the secondary is marked for the speaker impedance (“common”, 4-ohm, 8-ohm, etc.) and the primary is marked for wattage (“common”, 1/4W, 1/2W, 1W, 2W, 5W, etc.). With that type of transformer, the amplifier might connect between C and 5W, and the speaker between C and 8 for example but as I said, that's if you're lucky!
