A Guide To 100V Line Amplifiers

A specialist audio amplifier, used to distribute sound efficiently over long distances. Unlike standard low-impedance (4Ω or 8Ω) audio systems, which require careful impedance matching of speakers and amplifiers to prevent overloads and damage, a 100V line system allows multiple speakers to be connected to the amplifier without issue.

They operate using a high-voltage output (100V RMS max) which is approximately double that which a standard Hi-Fi style amp would be producing. This raised output voltage lowers the operating current, allowing the amplifier to run more efficiently and transfer power over long distances with minimal loss.

The amplifier works in conjunction with speakers designed specifically for 100V, which can accept the high voltage/low current signal and convert it back to the low voltage and higher current required to move the speaker’s low impedance driver.

The key points to a 100V Line amplifier and system are:

Amplification:

The same as any integrated audio amp, the incoming source signal is filtered through a built-in preamp first, allowing tone settings and signal gain adjustments. The amplifiers usually accept any audio signal at standard line level, so that could be a CD player, Bluetooth connection, Aux input etc. That preamplified signal is then fed through to the unit's power stage where its voltage and amplitude are enlarged considerably.

Channel Selection:

On single-channel 100V amplifiers you won't have this option, but for multi-channel output amps or matrix amps, you will usually have push buttons that allow the output zones to be selected, adjusted, and muted, independently of one another. On matrix units, you will also have switching and output channel assign options for the input channels.

Mono Summing:

100V amplifiers take a standard stereo line level input from your audio source and correctly combine the left, right, and ground elements into a full-range mono signal. This allows single speakers to produce a full output and avoids any odd phasing effects that would occur when trying to implement stereo in a multi-speaker installation. This is standard for commercial audio, including nightclubs and arenas, meaning you don't have to worry about ‘left and right’ when locating speakers.

Step-Up Transformer:

The output signal at the amps speaker terminals is raised from the normal 5V to 30V level of a Hi-Fi amp, up to 60V+ (100V RMS max), through a custom transformer. This large voltage rise reduces current (Ohms Law), and greatly increases the impedance, helping prevent power loss over long cable runs.

Step-Down Transformer:

Though physically not part of the amplifier, each 100V specific loudspeaker has a built-in transformer that reverses the step-up process, bringing the high voltage signal back down to a level the speaker can make use of. It's only the transformer that’s 100V, the speaker itself is still just a standard low-impedance type so needs a higher current, lower voltage signal to work.

Power Tappings:

Also part of the speaker's step-down transformer, the ability to ‘tap’ 100V speakers at different power levels is one of the most important parts of these systems. For example, a 30W RMS speaker may have taps from its transformer at 25W, 15W, 7W, 3W, and 1.5W. Wiring the positive line to one of these taps dictates the maximum current that the speaker will be able to pull from the amplifier.

Parallel Speaker Connections:

The use of stepping transformers also makes these high-voltage systems high-impedance, with the speaker's low-impedance voice coil being isolated electrically making it ‘invisible’ to the amplifier. This allows multiple speakers to be connected to the amplifier in parallel without impedance loading or mismatch concerns.

This setup ensures consistent audio quality and performance, no matter how far the speakers are from the amplifier, the number of speakers used, or the type of speaker. It allows for a single amplifier to operate ceiling speakers, wall speakers, and pendant speakers for example, all at the same time, on the same cable run, which is simply not possible with conventional, low-impedance audio equipment.

Having the ability to manually select and limit the speaker's current draw is a huge part of the 100V system. It allows you to accurately calculate the size of the amplifier and the thickness/type of speaker cable required for systems of any size, as the power usage of the speakers is always a controlled factor.

A ‘standard’ 100V Line amplifier is designed with a single output channel, meaning all connected speakers receive the same audio signal, and pull power from the amps power section at a fixed maximum wattage per speaker. The overall system is controlled by a single volume, and the speakers are connected in parallel to a single set of output terminals.

This is also known as a Single-Zone amplifier. You can still take multiple speaker cable runs to more than one room or area from these amps, but all will play the same music, and share the same single volume control. You only have a single set of speaker connections on the amplifier though, so would usually make use of an external terminal block to make wiring easier.

This setup works well for background music in shops, offices, and hospitality settings, and for most situations will be perfectly suited for the task, keeping things simple to operate and easy to connect. However, it may not offer the level of power or versatility that larger or more complex installations require, especially those that need an independent selection of music and volume to different areas.

This is where Multi-Zone amplifiers come into play. These more advanced amplifiers expand on the 100V line concept, enabling separate audio zones to be controlled from one central unit. This is particularly beneficial in buildings with multiple floors or distinct areas, such as campuses, hotels, or large commercial spaces, where different sections may need their own independent audio feed, separate volume control, or the ability to mute certain zones when required.

There are two distinct types of multi-zone 100V amplifiers, these being Single Input Source to Multi-Zone Output, and Multi-Input Source to Multi-Zone Output (Matrix):

Single Input Source to Multi-Zone Output

These work similarly to a standard single-channel 100V amplifier, taking a single audio feed from your chosen device and sending it out. The difference this time is that it will have between 2 to 6 output channels or ‘zones’ available. Think of it as a single input going to a splitter box, with each of those output channels playing back the same audio feed.

Single input is a slight misnomer, as most 100V amps will actually have more than one audio input available, so you may have a line-level RCA, a built-in media player with USB, a 3.5mm AUX, and one or several microphone inputs. What they mean by single input is the amp can only amplify one of these, so you select between them and that's what goes out to the system.

Each output channel will have its own volume control and will usually have a mute switch to quickly kill that zone. Some may also allow a paging microphone input to be directed to each specific zone, while emergency announcements will take priority over any music playing or any volume setting, playing across the whole system at full volume.

With single-input to multiple output amplifiers, each channel will have its own set of Common and 100V speaker terminals, which will either be spade connections or Pheonix/Euroblock connectors. These amplifiers will usually have only one step-up transformer, meaning the outputs share the available wattage with no restrictions, so load distribution across the zones is up to you.

IMAGE A shows a single source, multi-zone amplifier. It has 4 input source connections and built-in Bluetooth, USB Mp3, and Internet radio available under its ‘AUX’ section. It can only playback one of these sources to its 6 available output zones.

Multi-Input Source to Multi-Zone Output (Matrix)

A Matrix amplifier includes multiple inputs and outputs, each corresponding to a different zone, allowing independent volume adjustment and audio management. Effectively, it functions as both an amplifier and a built-in mixer, making it possible to output different music sources in different areas simultaneously.

As an example, a Matrix amplifier could have 4 audio input channels (plus mic input) and 6 output channels, with its inputs being built-in Bluetooth, an FM/DAB radio, RCA line-level inputs for CD players or laptop audio feeds, and an XLR for a paging microphone.

The 6 output channels will each feature push buttons to select which of the 4 input channels you wish that output to use, meaning you could have a Bluetooth stream playing in say 2 areas while you listen to a CD in another, and the radio in the remaining 3. Each output channel will also feature a mute switch, volume control and tone controls.

As with the single input design, the rear of these amplifiers will have connections for each output zone (so 6 in our example), making wiring easy to identify, which is especially useful when troubleshooting any issues with particular zones that may arise.

Matrix amplifiers are often more powerful than other 100V amps, as it's generally expected you will be running a larger system from them. One important factor to understand with Matrix amps is how they can differ in their power distribution methods:

• Output Type 1: As mentioned with single-input amplifier types, on many Matrix amps the output power is shared. So say it's 600W total and it has 6 output channels, you can load each channel however you wish, eg, 200W on channel 1, 100W on channel 2, 50W on channel 3 etc. The amp won't care, just as long as they all come in below 600W total. (we are ignoring the recommended 20-50% power buffer for these examples)
• Output Type 2: With other Matrix amps, however, the outputs are isolated (so six step-up transformers in place of just one), meaning the 600W is split equally, with 100W available to each of the 6 output channels. The total capability is the same, but this obviously can limit how many speakers, or the tappings on speakers, can be placed on each of the output channels or zones.

IMAGE B shows a multi-source, multi-zone amplifier. It has 4 input source channels with 3-band EQ and has a 5th channel for the built-in Bluetooth. The input assign buttons mean it can playback any of these inputs to any of its 4 output zones at the same time.

Taking the information we have just covered, choosing the right 100V line amplifier will depend on several factors you need to consider. These will include:

• The Type of Install: Where is the amp going? what number of rooms/zones or floors are there if it’s a larger installation? Is it even possible to run cables back to that one amplifier from all those areas? It may well be that some bigger installations require more than one amplifier.
• Audio Sources: Will you be playing MP3 files on a loop from a USB drive, listening to the radio?, or playing music from a CD player? Or will you want Bluetooth streaming from mobile devices to be available? Maybe you want to stream to the system from a service such as Spotify.
• Playback Options: Will all areas be playing the same music, or will the system be required to supply different input sources to different areas of the installation at the same time? If it’s to be a multi-room system, will there be a need for local volume controls? Will playback be accessible to a chosen few, or multiple staff members?
• Performance: Is the system purely for background music at an ambient volume, or will it be required to perform at higher levels in all or selected areas? Generally, 100V systems are intended for lower-level performance, but they are capable of more if the correct speakers and amplifiers are specified.
• Number of Speakers: Part of the performance consideration. How many speakers will there be per zone, and in total? You will need to decide on the number of speakers and their wattage settings in order to properly calculate the power requirements of an amplifier.
• Tannoy Functionality: While a standard feature on most 100V amplifiers, it’s still an important factor to consider if you require your audio system to allow for vocal announcements. Some amplifiers have features such as VOX/Priority override for their main microphone input, which when activated will mute any music playing, and turn on any channels that are muted, ensuring complete system coverage regardless of any local or remote volume control settings.
• Emergency Features: On top of the priority vocal override feature, some amplifiers also include inputs for a building’s fire alarm system, either muting all audio or providing a warning siren across the system at full volume when triggered.

Asking and answering these questions will immediately number your selection of suitable amplifiers to just a few, and will also inform you if it's even possible to do what you’re planning with this type of equipment.

You will find with 100V amplifiers that the same design is available in different power/wattage ratings, so you rarely have to compromise. The features remain identical, with just the output capability changing to suit installations of different sizes.

IMAGE C shows the similarities and differences of our own PRM range of amplifiers, from the PRM120 single source to single-zone amp, to the PRM360 single source to 4-zone unit, and the PRM606 Matrix, which has 5 input sources that can be assigned to any or all of the 6 output zones.

The joy of 100V systems is their versatility between amplifier and speakers, allowing you to easily adjust the power requirements of individual speakers or groups of speakers to bring them within the capabilities of that particular amp you have set your heart on. If your total speaker load is a bit too big for the amp, simply use lower-power tappings and make the maths work. Or, if that's not possible, you can look at the simple addition of extra amplifiers or slave power amps to get your output level where it needs to be.

Designed to provide extra power to a 100V audio system, a slave amp is a power amplifier only, requiring a line-level feed from the main amplifier. They can be used to power an additional zone from a single output amp, or can be used in a larger multi-room system.

You may have a lower-power amplifier and wish to expand the size of a system, or you wish to raise the power tap settings on your speakers, or even replace them with larger, higher output units. Obviously, you could just replace the main amplifier to achieve this, but that may not be ideal, and even upgrades are still relatively limited on power depending on their design, with higher output 100V amps still only being a maximum of around 360W.

With a single slave amplifier, you could easily double that power figure, which may sound extreme for background music, but a large installation could be driving hundreds of speakers across a variety of areas, with each of those areas or zones having its own ambient noise level for the sound system to overcome.

As an example for a larger system, let's say you are using a 6-channel Matrix amplifier for instance. You will usually have an RCA line output available for each of the amps output channels, allowing the easy addition of a slave power amplifier to each zone if required, providing huge power for a bigger system while retaining a single control point.

Whether it’s necessary or not depends on the type of speakers you plan on using, the desired volume level, and the level of system control that's required, but they are by far the simplest way to increase the power/wattage that's available to your 100V speaker system.

Before you ask, it’s worth mentioning you can't just use any old power amplifier though, as you still need it to output a 100V Line signal to your speakers, so a slave amp must be a 100V-specific design.

IMAGE D shows a PRS360 power amplifier. This is a 100V Line slave amp designed to match our PRM amplifier series. It takes a preamplified line signal from the main 100V amplifier and provides you with a single output with 360W RMS of power available.