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
a source is e.g. a pre-amplifier output or a
50
W
function generator output. To assess
the noise performance of the amplifier
without picking up interference, connect
the two input pins of the differential
connector together wile leaving the ground
pin in the middle open (Fig. 2).
The output noise will be lowered further
when the bandwidth of the amplifier is
reduced,
which
happens
when
a
significant capacitive load is connected to
the output. This will happen automatically
when a high-capacitance piezo is
connected to the output. For all other
cases, a shielded 1
µ
F 400V capacitive
load box accessory can be ordered from
Falco Systems for use with the amplifier,
which is connected in parallel with the load
(Fig 4). This will bring the noise down from
its value of ~50
µ
V
rms
(with a DC - 100kHz
bandwidth) to only ~20
µ
V
rms
(with a DC –
500Hz bandwidth), see Fig. 8 in the
Characteristics section. If used, always
connect the capacitive load box directly
next to the load, so that the box also filters
away the interference picked up by the
output cable before this interference
reaches the load.
For a comprehensive treatment on the
subject of noise and interference, the
reader is referred to the Falco Systems
application notes, online at www.falco-
systems.com.
Figure 4. The bandwidth- and noise reducing Falco Systems capacitive load is connected to
the load, the noise reduces to ~20
µ
V
rms
, while the bandwidth is simultaneously reduced to DC
– 500Hz.
Amplifier
diff. in
Generator
diff. out
Differential cable
+
+
-
-
Cable shield
Optional extra ground
(middle pin of connector)
Amplifier
Capacitor box
Load
