70-Volt Tests and Measurements
The best way to test / measure 70-Volt system components and speaker lines is to use a capable Impedance Meter. The Goldline ZM1P is one of the best, and most utilized Impedance Meters by Audio Technicians. Older Analog types of Impedance Meters were very good as well, but you had to calculate the math once you took a reading. The Goldline ZM1P does all the math for you – no need to get out your calculator to figure out the wattage. If you are working on, or installing 70-Volt systems it would be very beneficial to have one of these meters on hand. It will save you lots of time and grief during troubleshooting, but most of all ensure a “quality” installation.
How to Test a 70-Volt Speakers
Again, the fastest way to test a 70-Volt speaker would be to disconnect the speaker and try it on a different Line / Amplifier. This will also tell you if there’s a line or amplifier issue as well. But, if you are pretty sure that the issue is with the speaker, here are some tests you can try to verify whether or not the speaker is defective or not?
Using an Impedance Meter to test a 70-Volt Transformer (Watts Test)
The test below includes an 8-ohm speaker and 70-Volt transformer tapped at 8 watts. The first step is to always disconnect the speaker line from the back of the amplifier. Then, connect the 8-watt tap (Yellow wire) to the Red lead of the meter, then the transformer common (black wire) to the black lead of the meter. Set the Meters Function to Watts, Range to 20 Watts, Frequency to 1K tone, and the Voltage to the 70V setting. Turn the meter on. You should hear an audible tone coming out of the speaker, and get a wattage reading on the meter (see below).
In the example (shown below) we have the Impedance Meter leads on the 8-Watt tap wires, and we get a reading of 8.06 Watts, which is very close.
Using a Multimeter to test a 70-Volt Transformer
If you do not have access to an Impedance Meter here is a quick test you can perform using a Multimeter. Note: Understand that when testing 70-Volt Systems, using an Impedance Meter is always preferred. The test below (right) has a 70-Volt transformer that has been disconnected from the amplifier and the speaker. This is not a “Wattage” test – This test lets you know if the transformer is Open, has a Short, or how much Resistance is on the different taps. In the first measurement we will test the 2-watt tap (the orange wire). First, connect the Red lead of the meter to the orange wire, then the transformer common (black wire) to the black lead of the meter. Set the meter to 200 Ohms. We get a reading of 47.8-ohms on the 2-watt tap. Next, we will test the 8-watt tap (yellow / black wires on transformer) and we get a reading of 21.9-ohms. These would be “normal” readings for this transformer. Notice that as the tap wattages get higher, the ohms reading gets lower. If this is still the case when you measure the remaining taps – it’s a good sign that the transformer is working. A quick test without using an Impedance meter.
Note: As you are measuring the taps on the transformer you should document the readings (as you go) so you can verify the measurements, and also save the info for any future measurements. If any of your measurements indicate an “Open or a Short” – there is likely an issue with the transformer.
Testing 70-Volt Speakers – Ohms Setting
Ex: 1 Has the Impedance meter using the “Ohms” setting. The 8-ohm speaker connected to a 70-Volt transformer, tapped at 8-Watts. With the “Ohms” setting – the meter will read the speakers impedance through the transformer – which is 8.06-ohms (which is very close to the speakers 8-ohm rating).
Ex: 2 If using a multimeter, you cannot read the speakers impedance with it connected to the 70-Volt transformer – disconnect the speaker, and test the speaker’s impedance directly. The meter reads 8.1-ohms which is about the same as the impedance meter (and very close to the speakers 8-ohm rating).
Tech Note: Testing 70-Volt transformers and speakers is somewhat tricky in a sense, and it’s best to use an Impedance Meter. If you don’t have an Impedance Meter, then a regular Multimeter can assist with some aspects of troubleshooting. With that being said – when troubleshooting a 70-Volt speaker (with built-in transformer) you will need an Impedance Meter!
How to Test a 70Volt Speaker Line
In order to properly test a 70-Volt speaker line you will need an Impedance Meter like the Goldline ZM1P (pictured right). This meter will display calculated impedances and power for constant voltage systems. Basically, this meter will apply a constant voltage to the line (load) and automatically calculate the wattage without the technician having to do any math!
