Pump Station 16-R: Installation and operation manual 9
16 Chassis Ground Terminal
The rear panel of the Pump Station 16-R is fitted with a Chassis Ground Terminal – this should
be terminated to a convenient earth terminal on the mains distribution system. The termination
is provided for protection purposes; this unit is normally connected to a number of TV sets, FM
receivers and satellite receivers and the grounding of the Pump Station 16-R is a safety
measure to protect the users of the system.
17 Solving problems
17.1 Ground loops (aka Earth loops)
Despite your best efforts, the completed sound system may have some audible ‘hum’, if this is
the case you probably have a ‘ground loop’; this is usually caused by introducing an additional
ground on one of the signal sources. One technique to find the offending signal source can be
undertaken by monitoring the ‘hum’ then disconnecting the input leads (both left & right
channels) on each line input until the ‘hum’ disappears. This problem is often caused by
terminating a screened input cable into a signal source positioned a significant distance from
the mixer. A good way of avoiding this potential problem is to use signal sources (CD players
and the like) that are double insulated with no connection to the mains supply earth. In some
instances the problem can be resolved by insulating the front panel of the signal source from
the equipment rack. If a signal feed is derived from a second mixer (a club or microphone mixer
for example) it would be perfectly normal to expect this to be earthed; we suggest that a
transformer be used to isolate the signal and prevent a noisy loop.
17.2 Connecting balanced signals to the unbalanced line inputs.
We recommend the use of a transformer to convert a balanced signal to an unbalanced signal
suitable for direct connection to the mixer line inputs. The transformer should be mounted close
to the Pump Station 16-R and the unbalanced output lead should be kept as short as possible.
Where both the source unit and destination mixer are earthed, it is important to isolate the
primary and secondary windings to avoid a potential ground loop; if there is any doubt about
this, we suggest that the balanced cable screen is not connected at the transformer end.
Suitable transformers for this application are the RS Components 210-6447 (primary &
secondary series connected) we recommend the fitting of a screening can also from RS (part
number 210-6469); Canford Audio supply a similar transformer OEP Z1604 we again
recommend that this should be fitted in a similar screened housing. All transformers should be
wired to give a ratio of 1:1. A diagram showing the transformer wiring can be seen below.
BALANCED TO UNBALANCED INTERCONNECTION
( WITH ISOLATION TO PREVENT GROUND LOOP )
BALANCED
SIGNAL
INPUT
DO NOT CONNECT CABLE
SCREEN AT THIS END
PRIMARY SECONDARY
+
+
--
SCREEN
INPUT
HOT
OUTPUT
TO MIXER
LINE INPUT
AUDIO
TRANSFORMER
1 : 1
16-07-02 V2.1
(28 pages)
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