70V vs 100V Line Systems: A Complete Guide to Constant-Voltage PA

If you are installing public address in a large building or across a campus, a constant-voltage (70V or 100V) line system is almost always the right choice. Here is how it works and why it matters.

What is a constant-voltage system?

In a traditional low-impedance system, the amplifier drives speakers directly at 4Ω or 8Ω. Over long distances this loses power to cable resistance and limits how many speakers you can connect. A 70V or 100V line system instead steps the audio up to a higher voltage using a transformer at the amplifier, then each speaker steps it back down with its own small transformer.

Why it matters for large installations

• Long cable runs with minimal power loss.
• Many speakers on one line — simply add speakers until you reach the amplifier’s wattage.
• Easy design — each speaker has a wattage tap (e.g. 5W, 10W, 20W); add up the taps and stay under the amplifier rating.
• Consistent volume across every speaker regardless of distance.

70V or 100V — which should you choose?

Electrically they are the same idea at different voltages. 100V allows longer cable runs and more speakers for a given wire gauge, and is the global standard for large installs. 70V is common where shorter distances or specific safety codes apply. Every World Tone amplifier provides both 70V and 100V taps, so you are never locked in.

How to size the amplifier

Add up the wattage taps of every speaker, then choose an amplifier with at least that much power plus 20% headroom. For example, forty 10W ceiling speakers total 400W — a WTX-5001 M (500W RMS) covers it comfortably. For bigger campuses, step up to the WTX-10000 DP.

Best World Tone amplifiers for line systems

For distributed PA, look at the single-channel range — every model offers 70V/100V outputs. For multi-area buildings, a two-zone amplifier like the TZA-10000 DP lets you run two independent 100V lines from one chassis.