Falco Systems WMA-200 User Manual page 4

Cabling
The WMA-200 high voltage amplifier has
been designed for use in the most
demanding low noise experiments. As
such, the noise generated by the amplifier
is so low, that the actual performance of
the set-up in which it is used can easily be
dominated by interference picked up from
the surroundings. For optimal performance
use the differential input, with a high
quality differential cable such as STP
(shielded twisted pair), and keep the cable
as short as possible.
As the output connector is a single-ended
BNC, all interference picked up by the
output cable will be directly appear across
the connected load.
performance of the amplifier has been
Figure 2. Assessment of the ultimate attainable output noise level of the WMA-200 high
voltage amplifier requires care not to beak the coaxiality of the connection. Cables should be
as short as possible (or even absent, as in this example) not to pick up any interference,
which will appear directly across the load. The differential inputs are shorted together at the
Generator
diff. out
Figure 3. Cable arrangement recommended for the WMA-200
Noise
The noise of the amplifier is lowest when a
low-impedance source is used, because
then the 1kΩ input resistors cannot
contribute to the overall noise level. Such
assessed with the inputs shorted, and the
output of the amplifier connected with a
direct coaxial connection to a low-noise
oscilloscope front end. Fig. 2 shows the
arrangement. Even a 10 centimetre output
cable increases the attainable noise level
by a few microvolts in a typical setup due
to interference pick-up. But this may not
be a problem in many applications; the
performance
conventional standards when a longer
coaxial cable is used. It is recommended
not to make a ground connection to the
load in any other way than via the WMA-
200 amplifier output connector ground, to
prevent
arrangement of connections is given in
The noise Fig. 3.
amplifier input in this example.
Differential cable
+
-
Cable shield
a source is e.g. a pre-amplifier output or a
50Ω function generator output. To assess
the noise performance of the amplifier
without picking up interference, connect
the two input pins of the differential
is still
ground loops.
+
Amplifier
-
diff. in
Optional extra ground
(middle pin of connector)
excellent by
The optimal