This section is intended to provide some useful background information on mic splitters.

Introduction

In its very basic form, a splitter accepts mic/line signals and splits each signal for distribution to a number of different processing devices. However, more advanced solutions are required to cope with factors within a sound system that cause signal degradation and produce external noise and radio frequency (RF) interference. These factors include the number of splits required and the length of cable runs, and also the inherent problems imposed by the low level of the mic signal and multiple-grounding. The types of splitter and how they are designed to overcome these problems are discussed in further detail in the following subsections.

Active splitter (Square ONE Splitter)

An active splitter uses active electronic circuitry to address the problems inherent in passive (parallel and transformer isolated) splitter systems.

An adjustable gain stage is added at the front end of the split allowing the user to add a pre-determined amount of gain to the low level mic signal early in the system signal path. This is then buffered, electronically balanced and driven anywhere up to or at line level (making the signal relatively safe from external interference) before being sent on to the attached mixing consoles. This approach reduces the length of sensitive mic cables to a bare minimum, which dramatically improves audio performance by reducing cable losses and additional noise, and also keeps the mic loading normal, resulting in a far brighter and more accurate sound. Ground lift switches are provided on the electronic outputs to enable isolation, if required.

In addition, a transformer isolated output - normally derived as a copy of the post-preamp signal, but on the Square ONE Splitter is tapped off before the gain stage - is buffered and driven, making it relatively safe from external interference. This would typically be used for broadcasters who prefer to add their own gain and may also be running their system from a different power source.

Other useful features usually included with an active splitter - and especially on the Square ONE Splitter - are local metering, +48V phantom power and a solo system with headphone output to allow local monitoring.

Isolated splitter

An isolated splitter typically uses a 1:1:1:1 ratio transformer to achieve the audio isolation. The mic input signal is connected to the primary winding of the transformer, with all of the split points derived from the secondary windings. Additional 'ground lift' switches may be added to each of the split points providing the option to fully isolate individual parts of the system, if required.

Isolated systems are the next step up from a passive system and offer a big increase in performance, although this comes at a price. To get the best out of an isolated system a very high quality transformer is required, which is expensive.

Although the isolated splitter addresses one of the fundamental problems inherent in passive systems by providing isolation, it doesn't solve the problem of sensitive low level mic signals being carried over long distances and their susceptibility to picking up additional noise from other sources, which is ultimately amplified at the mixing console. When using a 1:1:1:1 ratio transformer the loading on the mic and the extra capacitance remains, resulting in high frequency loss. Also, the input impedance of each console added to the system will reduce the overall level. There are 3:1:1:1 ratio 'step down' transformers available that compensate for the high frequency loss by lowering the gain.

Phantom power (+48V) will also need to be provided for the mics, which may entail connecting one of the consoles in a passive parallel splitter-type configuration or adding a separate supply.

Passive parallel splitter

The passive parallel splitter has, basically, all of the 'split' points wired in parallel, offering no ground isolation or any gain stage whatsoever. Passive parallel splitters are popular at the lower end of the market as they provide a very cost-effective solution as compared with a transformer isolated splitter or an active splitter.

There are four fundamental problems inherent in a passive parallel type splitter:

• Mic signals are typically very low level (-40dB), with the gain being added at the mixing console. Due to the nature of a passive parallel splitter system the cable runs carrying the mic signal end up being quite long, increasing their susceptibility to picking up additional noise from other sources, for example, stray mains cables that may induce hum. In turn, this additional noise also gets amplified along with the original mic signal.
• The lengthy mic cable runs also significantly increase capacitance, which in turn reduces the high frequency content making the sound dull and uninspiring. Also, the input impedance of each console added to the system will reduce the overall level.
• Phantom powered mics are normally supplied via two 6k8 ohm resistors. If additional +48V sources are enabled in parallel this increases the current and voltage, potentially damaging the mic.
• The grounding regime is basically one complete ground with no option of isolating various parts of the system. This can potentially lead to ground loop problems if parts of the system are powered from different sources. For example, the PA company may have set the whole system up perfectly using one grounding regime, an independent broadcaster then arrives and has to use a portable generator, adding another grounding source.

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