Niles Audio HDL-4 - Manual (Page 7)

Avoiding Interference
Speaker wires can act as an "antenna" for electrical noise.
Locating speaker wires too close to a light dimmer or switch
may cause a "buzzing" or "popping" sound to be heard
through the speakers. If you must locate the HDL-4 wiring
near electrical devices, route the speaker wires several feet
away from the electrical wiring.
Using the HDL-4 with Tube-Type Amplifiers
Virtually all tube amplifiers must have a load connected at all
times. If the amplifier to be connected to the HDL-4 is a tube
amplifier, be sure to always have at least one pair of speakers
switched on at all times. An alternative is to permanently
connect a 150 ohm, 5 watt resistor across the tube amplifier's
output in parallel with the HDL-4. See (Figure 1) on next
page for hookup diagram.
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