INTRODUCTION The Models 452 and 852 are versatile dual-channel filters consisting of two identical channels in a common cabinet. Each Filter channel has separate input/output terminals, offers high pass and low pass functions, 0 dB and 20 dB gain, Butterworth and Linear Phase responses and 3~digit resolution for cutoff frequency selection. Individual channels may be readily interconnected for series or parallel operation, resulting in bandpass (or doubled rolloff) and band reject functions respectively. Each Filter channel provides switch selectable Flat Amplitude (Butterworth) response and Flat Delay (Linear Phase) response. The Butterworth Filter has maximally-flat amplitude response suitable for frequency-domain applications. Its cutoff frequency (fc) is defined as the frequency at which the amplitude response is down 3 dB. The Linear Phase Filter approximates a constant time delay for frequencies below its cutoff frequency. This Filter is suitable for time-domain applications because of its inherent ability to pass transient waveforms with a very small amount of distortion and overshoot. Models 452 and 852 are electrically and mechanically similar, covering the cut off frequency range of 0.1 Hz to 111 KHz. Rol loff of the model 452 is 24 dB/ octave/channel, model 852 is 48 dB/octave/channel. Factory installed Option -01 extends cut off frequency range and resolution on both models to 0.01 Hz. Frequency-determining passive elements of the filters consist of stable precision metal film resistors and close tolerance polycarbonate or mica film capacitors. The active elements are FET-input IC operational amplifiers which provide highly stable gain, and very low noise and distortion. This combination of active and passive elements produces a Filter having high cut off frequency accuracy and resettability, and excellent temperature and long term stability. Another result of precise control of frequency-determining elements is close amplitude and phase match between channels. ELECTRICAL. Models 452 and 852 operate from either 115 or 230 volts ac, 50-500 Hz, and consume less than 5 watts of power. A rear-panel slide switch selects the nominal line voltage. The case of the instrument is grounded through the power cord, but signal ground can be isolated from power ground (through a 0.01 µf capacitor) via a rear-panel slide switch. Cutoff frequency of each channel is selected via three 11 -position (0-10) switches and a 4-position multiplier switch* The two pilot lights also serve as cutoff frequency decimal point indicators. Passband Gain of 0 dB or 20 dB may be selected for each channel. High Pass or Low Pass mode is individually selectable for each channel, as well as Fiat Amplitude or Flat Delay response. MECHANICAL. The instrument cabinet is 3.5 inches high by 17 inches wide (1 9 inches wide including rack mounts). It is 13 inches deep and weighs 1 0 pounds (model 452) or 12 pounds (model 852). The power switch, operating controls, and input and output terminals are located on the front panel. The rear panel contains duplicate (parallel) input and output terminals for each channel, power connector, the fuse holder, the 115/230 Vac line selector switch, and a switch to disconnect signal ground from the power ground. In its standard configuration the instrument is supplied in a cabinet suitable for table-top use, with feet and tiltstand, A rack-mount configuration is also available (See Options).