The Krohn-Hite Model 3901 programmable, two channel, high-pass/low-pass elliptical filter/voltage gain amplifier is one of a family of programmable filters from Krohn-Hite. As an elliptical filter, the Model 3901 has two independent filter channels, one low-pass and the other high-pass, allowing for band-pass operation with atunable cutoff frequency range from 1Hz to 99kHz and a role-off rate of 115dB/octave. Each filter section has aminimum stopband attenuation of >80dB and apassband ripple oftypically 0.22dB. The 3901 provides either a single-ended or differential input with a common mode rejection of >60dB. Input gains up to 40dB in 10dB steps and output gains to 20dB in 10dB steps are also provided. The 3901 will accept input signals of ±10V peak at 0dB gain and has selectable ac or dc coupling. The filter is GPIB bus programmable and is complimented with non-volatile memory for storage of up to 99 front panel set-ups. Overload detectors are standard and assist the user in detecting excessive input signals or incorrect gain settings. The 3901q is also a programmable voltage gain amplifier for applications that require a low-noise amplifier. The amplifier has a bandwidth of 1MHz and gains to 60dB, selectable in 10dB steps, and a wideband noise <100μν. Typical applications for the Model 3901 are: distortion measurements, separating specific bandwidths of information, enhancing signal-to-noise ratio, low noise pre-amplification and many more.