  A low noise constant current source used for measuring the $1/f$ noise in
disordered systems in ohmic as well as non-ohmic regime is described. The
source can supply low noise constant current starting from as low as 1 $\mu$A
to a few tens of mA with a high voltage compliance limit of around 20 Volts.
The constant current source has several stages which can work in a standalone
manner or together to supply the desired value of load current. The noise
contributed by the current source is very low in the entire current range. The
fabrication of a low noise voltage preamplifier modified for bias dependent
noise measurements and based on the existing design available in the MAT04 data
sheet is also described.
