wires should be kept well apart from each other. To avoid interference maintain a separation
of at least 300mm.
4. Instability can cause the amplifier to run hot and may result in the TEMP LED illuminating.
Interference
1. Background magnetic field signals or interference may be present in any location and may not
be anything to do with the loop system. Monitor this with a loop receiver (such as an ILR3). If
the interference is still present with the loop system switched off, then you need to locate and
eliminate the source of the interference before switching the loop system back on
2. Magnetic fields can induce currents into any low impedance electrical path or loop. Audio or
video systems with multiple earths may experience pick up of the loop signal. Check entire
sound system for evidence of loop signal, and trace source of pick up.
3. Under certain circumstances, the loop signal may appear as jagged lines or hum bars on a
CCTV picture. This could be due to running CCTV (low impedance unbalanced 2-wire circuit)
cables in close proximity to the loop cable. Separate the loop cables to reduce the effect.
4. Remote (and apparently unconnected) PA systems can sometimes pick up loop signals. This
is usually because the loop cable becomes damaged (see point 1 of Instability) or induces
signals into the remote system through long unbalanced cables. Always run long audio signal
cables as 3-wire balanced circuits and keep away from loop cables.
5. See also point 1 of Instability
Failed AC power fuse in rear of unit
Unplug the loop and AC power supply from amplifier, and replace the failed fuse with the spare fuse
in AC power input fuse tray.
Reconnect the AC power supply and switch on. If the fuse fails again, return the unit to Ampetronic
for evaluation - it may well be covered under warranty, which will be invalidated by removing the
cover. If the fuse does not fail a 'loop error' may be indicated, but shows that the unit is working
correctly. Re-connect the loop and switch the power off then on again to reset loop error.
If the fuse fails when the loop is re-connected to the unit, then the loop could be shorted to
electrical mains (and building) earth. This can happen even if no audio signal is present, as the
short to earth is likely to cause an instability / oscillation / feedback condition to develop. A loop
cable short to earth most commonly occurs where flat copper tape is installed on a metal-clad
raised access flooring system. If the insulation on the flat copper tape is abraded (for example by a
piece of metal swarf trapped below the copper tape), the conductor could short to the earthed tiles.
When installing on raised access floors, it is advisable to insulate beneath the flat copper tape
installation using Ampetronic PWT or similar tape.
The loop short to earth may only be completed when a person steps on the tape in the affected
location, which can create significant difficulties when diagnosing the cause of fuse failure. Contact
Ampetronic for further advice if a unit is suffering recurring but untraceable failure of the rear panel
fuse.
ACCESSORIES
Details of all products and services provided by Ampetronic can be found at www.ampetronic.co
Ampetronic MLD5 Installation Handbook
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