Clean and in excellent condition. Two-channel low pass filter with RS-232, GPIB and rack mount kit

The SR640 is a Dual-Channel Programmable Low Pass Filter. Each instrument channel has a low-noise preamplifier, two precision high-pass filter sections, and an output amplifier. The filter is an 8-pole, 6-zero elliptic-type with 115 dB per octave rolloff, 0.1 dB of passband ripple, and 80 dB stopband attenuation. Cutoff frequencies can be set between 1 Hz and 100 kHz, making the SR640 ideal for applications including anti-aliasing, audio analysis, and general frequency-domain signal conditioning.

Each filter channel has a floating, differential input with 1 MΩ input impedance and 6 nV/√Hz of input noise. The analog ground for each filter channel is available at a rear-panel BNC connector to provide complete flexibility in grounding. The filter grounds may be tied to the instrument's chassis ground or to any other point. Both AC and DC input coupling can be selected, and an invert key allows the phase of the signal to be shifted by 180° with a single key press. Up to 60 dB of preamplifier gain can be specified in 10 dB increments. A simple offset adjust screw lets you null DC components in your signal.


  • Two independent filter channels
  • 115 dB/octave rolloff
  • 1 Hz to 100 kHz frequency range
  • 0.1 dB passband ripple
  • 6 nV/√Hz input noise
  • Up to 80 dB of gain
  • GPIB and RS-232 interfaces