The SR560 is a low-noise preamp with configurable filters sold by Stanford Research. We use it all over the place to do semi-low noise measurements and for use in temporary servos.

Manufacturer's web site

Tips & Tricks

1. The SR560 only has 'low noise' (input referred noise of ~5 nV/rHz) above 100 Hz and with a gain > 100 and with the low noise setting ON. With low gain, the input referred noise is more than 100 nV/rHz. Its also noise low noise at low frequency. Look at the manual on the website for the actual noise curve. Often, the SR560's that we have been using in the field get a little damaged and the input referred noise gets worse by as much as a factor of 2-3.

2. It has a 50 Ohm output which is handy for driving low impedance loads (e.g. speakers).
3. Since it uses discrete FETs (the obsolete NPD5564), it has a very high input impedance (100M).
4. The internal batteries are lead-acid. Deep discharge should be avoided. ALL SR560's must be kept hooked up to the AC power when not in use to prolong battery life. The batteries are expensive enough that it is certainly worth your time to hook them up after each measurement. Don't be lazy!!
5. The AC coupling corner frequency is 30 mHz.
6. There is a little offset trim on the front panel. This must be zeroed when using the SR560 as a servo block. Sometimes the trim pot screwhead is a little offset from the front panel hole, so be careful in placing the trimmer screwdriver. It should be flathead and also one of the smallest ones from the jeweler's screwdriver set.

Trouble Shooting

1. If there is an offset which won't go away with the input shorted, you may have to open the box and use the calibration/repair procedure in the box.
2. If that doesn't work, most likely the front end FET pair is damaged. You need to somehow find a replacement and replace it.