As we explained last month, the vast majority of build-it-yourself and commercial (hi fi and PA) amplifiers are voltage amplifiers, whereas hearing loop amplifiers are current-operated devices. That’s not to say you can’t use a voltage amplifier on a hearing loop – you can, with appropriate treble boost to compensate for rolloff in signal strength due to loop inductance.
But typical amplifier treble controls are not suitable because they do not operate at the correct frequency. There is a better way, and that is to “pre-condition” the audio feed to the amplifier – and we’ll shortly be describing such a device. It’s quite simple and relatively cheap (especially if that means you don’t have to buy a new hearing loop amplifier).
This month we’re going to look at some of the commercial hearing loop amplifiers often found in public buildings. These are the ones often installed by professional organisations who are these days fitting out most new buildings and retro-fitting olders ones, as we also explained last month.
Auditec's model 1077 transconductance amplifier (another way of saying current amplifier!) designed specifically for hearing loop use. It can drive a loop between 40m and 150m long.
Auditec hearing loop amplifiers
The Auditec (www.auditec.com.au) range of hearing loop amplifiers is an example of what is available commercially. This Australian company designs and manufactured its range locally and offer a five year warranty. The Auditec 1077 amplifier shown here is in a 2-unit rack mount case. Lower powered amplifiers are built into a smaller instrument-style case.