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The SR554 is a low-noise, transformer-coupled preamplifier optimized
for source impedances between 0.05 Ω and 1 kΩ. With
an input noise of only 0.1 nV/√Hz, the SR554 can be used in
a wide range of low-noise applications. It is the ideal preamplifier
for low-temperature synchronous detection applications where isolation
between the experimental sample and the lock-in amplifier is critical.
The SR554 can operate in one of two modes. In the "bypassed"
mode, the instrument is simply a passive transformer with a turns
ratio of 100, providing an overall voltage gain of 100. In the "non-bypassed"
mode, an additional amplifier with a gain of 5 is added increasing
the gain to 500 and providing a low-impedance (<1 Ω) output.
In the bypassed mode, the SR554 requires no external power. When
using the output amplifier, ±20 VDC must be supplied. The
preamplifier connector on SRS lock-ins can be used to power the
SR554.
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