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OPERATING INSTRUCTIONS
The SR552 Voltage Pre-Amplifier is designed to
be used with either the SR510/530 lock-ins as
well as the newer DSP lock-ins. The SR552
reduces the input noise and extends the full
scale sensitivity to 10 nV (without expand).
When used as a remote pre-amplifier, the
SR552 can eliminate the effects of noise pickup
on long signal cables.
Power and control are supplied to the SR552 via
the 9 pin cable which is supplied with the unit.
Attach one end of the cable to the connector on
the rear of the SR552. With the lock-in power
off, connect the other end of the cable to the
PRE-AMP connector on the rear of lock-in. Both
ends of the cable are equivalent. If a longer
cable is required, any standard 9 pin cable will
suffice since all connections are straight
through. When the lock-in power is on, the
POWER indicator on the SR552 will light.
CONNECTING THE SR552
The (A) Output of the SR552 should be
connected to the (A) Input of the lock-in. For
most applications, this single connection will be
adequate. The lock-in Input Selector should be
set to (A). For situations where there may be
noise pick-up on this cable, it is better to connect
the SR552 (B) Output (shielded pre-amp
ground) to the (B) Input of the lock-in as well.
The (A) and (B) cables should be twisted
together to prevent inductive pick-up. The lock-
in Input Selector should then be set to (A-B).
The SR552 (A) and (B) Inputs should now be
used as the lock-in voltage inputs. The input
switch selects single ended, (A), or differential,
(A-B), operation. The input impedance is 100
kΩ, 25 pF. The connector shields are isolated
from the chassis ground by 10 Ohms. These
inputs are protected to 100 Vdc but the ac input
should never exceed 10 V peak. The maximum
input before overload is 70 mV rms. The
OVERLOAD indicator will light whenever the
pre-amplifier overloads. Note that overloads
that occur after the pre-amplifier are indicated by
the lock-in's overload indicator.
USING THE SR550 WITH THE SR510/530
The SR510/530 lock-ins sense the presence of
the SR552 through the power cable and takes it
into account when setting the gain of its own
amplifiers. Thus, to obtain the correct overall
gain, the SR552 output must be connected to
the voltage inputs of the lock-in.
The overall sensitivity of the lock-in plus the pre-
amplifier is displayed as the sensitivity on the
lock-in front panel. It is necessary to divide the
displayed sensitivity by 10.
The gain of the SR552 is 10, 20, 50, or 100.
The gain is controlled by the lock-in and is set to
maximize the pre-amplifier gain while
maintaining the selected dynamic reserve. For
most sensitivities, the pre-amplifier gain will be
100. The following table summarizes the gain
allocation.
SR552 Pre-Amplifier Front Panel and Rear Panel