High impedance installations, also known as 70V or 100V lines are commonly used in applications where the following requirements are met:
In this kind of installations, a transformer is attached to the amplifier output so that the voltage output is up-converted either to 70 or 100V. On the loudspeakers side, another transformer will down-convert the 70 or 100V voltage to a voltage that can be held by the loudspeaker at low impedance.
The transformers are passive components that have a high inductive behaviour, which influences the general frequency response of the system. The more power a transformer must be able to hold, the most difficult is to keep a flat frequency response in the audio spectrum.
Fig. 1: Typical high impedance diagram with step-up and step-down transformers
The step-up (or output) transformer can be avoided at the amplifier output, when the amplifier has an output voltage swing exactly in the range of 0 to 70V, or 0 to 100V. In that case, the signal will be received directly by the transformers at the loudspeakers’ side. This brings a number of advantages to the installation, being the following the most relevant:
Fig. 2: High impedance diagram with HD Series (without step-up transformers)
Some of the Amate Audio HD Amplifiers comply with the requirements to be used in 70 and 100V lines without output transformer. The suitable models are:
Table 1: Suitable HD Amplifiers for high impedance installations