Aphex
Thermionics
- Division of Aphex Systems Ltd.
Page 5-2
Installation Instructions
out experiencing hum problems.
5.9 Lightning Protection
The Model 1100 MkII is not any more prone to
spike damage than other studio equipment, so
following good standard practices for lightning
protection should prove sufficient.
If you are in an area that is frequently hit by light-
ning storms you should use lightning arrestors
on all ac power lines and have local spike protec-
tors where equipment is plugged into the power
source. In areas where audio cables may be sub-
jected to lightning spikes, you should pay close
attention to how equipment is grounded making
sure the lightning rod cable does not travel paral-
lel to or near to any of your audio wiring.
5.10 Preparing Your Cables
Please refer to section 4, Interfacing & Cables, for
instructions on proper wiring.
5.11 Overcoming Ground & Hum Problems
In studio and live sound venues, it is often a
problem to establish a good ground system. You
may encounter existing systems where ground-
ing was never planned, or you may encounter,
simply, a wrong grounding strategy extensively
implemented.
Wherever hum and noise problems are endemic
you may be sure the ground system is faulty.
Dealing with that can be treacherous but with
simple understandings you can usually get con-
trol.
The most common ground problems come from
the a.c. house wiring. The wall outlets of adja-
cent walls in a room are normally sourced from
alternate phases of the power distribution panel.
When equipment is plugged into both sets of wall
outlets, there can be a voltage difference between
the neutrals and outlet grounds. That voltage dif-
ference generates ground current loops through
your equipment and consequently through your
audio wiring. The best way to stop these prob-
lems is to reassign the power distribution panel
so all outlets in the same room are from the same
power phase. If that is not possible, then you
should consider placing suitable power isolation
transformers in your room to isolate the equip-
ment power from the house wiring.
When possible, you can plan the house wiring
to include insulated ground wires and use hos-
pital grade outlets that keep the outlet ground
isolated from the conduit and box. With all insu-
lated ground wires bonded to the distribution
panel ground bus, a “star ground” is established
that eliminates most of the ground loops.
In the worst case, when you cannot in any way
correct the house wiring problems, then you
may need to distribute power to your equipment
only from the outlets of one wall by using power
strips. If you do this, be very sure the circuit does
not become overloaded. Check the rating of the
circuit breaker servicing those outlets and survey
the total load including any appliances that may
be in another room on the same breaker. You
may become lucky and find a pesky hum problem
can be eliminated simply by getting the right two
pieces of equipment onto the same outlet and
leaving everything else alone.
5.12 Radio Interference (RFI)
We designed the Model 1100 MkII to reject radio
interference, but if the level of interference gets
strong enough it will break through. If you experi-
ence TV “sync buzz” or taxicab calls in your audio,
then you must isolate the source of the RFI. It may
come through the mic cable, but it can also get in
through the power cord or other cables plugged
into the unit such as the insert send and return
lines. Try moving the power cord and cabling
around to minimize the effect. You may need to
install a power line filter if you are located near
a broadcast station. Keep all wiring as short as
possible.
