What Are Induction Loop Amplifiers - I-AMP GPT 60-IV User Manual

What are Induction Loop Amplifiers?

Induction Loop Amplifiers are designed to produce a base band magnetic field within an area covered by a
loop of cable, the induction loop. Magnetic fields are generated by current within the induction loop cable.
This magnetic field then allows direct transmission to a hearing aid fitted with a T-Coil.
Most hearing aids are fitted with a T-Coil which allows the user to select between the normal microphone
pick-ups or the T-Coil. If the T-Coil is selected, the hearing aid user will only hear the signal transmitted over
the induction loop.
Induction loop systems are the only hearing impaired augmentation system which does not require headsets
to be distributed to the hearing impaired due to this T-Coil function.
Why do we need to have Induction Loop Amplifiers?
Hearing aids are the most common method currently in use for the augmentation of sound to an individual.
These hearing aids detect the sound via a microphone in close proximity to the hearing aid user, amplify the
signal then re-transmits to the ear using an internal speaker. This arrangement can lead to the following
problems, all caused by the acoustic transmission path:
Limited volume or loudness can be obtained at the hearing aid due to acoustic feedback. This is heard as
squealing of the hearing aid speaker.
The Omni-directional characteristics of the hearing aid microphone cause unwanted sounds to be mixed
with the desired sounds. Internal room reverberation compounds this problem. The signal to noise ratio in
the acoustic transmission path can be very low in some environments.
Induction Loop Amplifiers provide a method of overcoming many of these short comings of hearing aids
when used with the internal microphone.
How do they Work?
The induction loop power amplifier is a specialized amplifier that is designed to supply a variable current
into the induction loop for a variable input voltage signal. This means that the induction loop power
amplifier is not like a conventional speaker power amplifier which outputs a given voltage for a given input
voltage (a voltage amplifier). Since an induction loop power amplifier has input voltage and output current it
is termed a "transconductance" amplifier. An interesting characteristic of a current output is that the output
voltage will vary dependent on the load impedance, but the current output will remain constant, independent
of the load.
The I-AMP range of induction loop power amplifiers feature a number of internal signal processing
functions. These include fast limiters to limit the maximum output current and protect the output electronics
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