Measures total distortion down to 0.1% full scale at any frequency between 5 cps to 600 kc; harmonics are indicated up to 3 mc. Model 331A includes a sensitive wideband solid-state voltmeter which may be used separately for general-purpose voltage and gain measurements. This instrument measures noise and hum as small as 50 microvolts over a wide range of level and frequency.

The distortion analyzer consists of a broadband amplifier, a tunable frequency-selective rejection circuit and a high-impedance voltmeter. The solid-state rejection circuit utilizes a capacitively tuned Wien bridge network which provides greater than 80 db of fundaniental rejection. Maximum input sensitivity at 0.1% distortion setting corresponds to 300 ~v rms for measuring low-level residuals. Input impedance is one megohm for both voltmeter and distortion operation with a single input terminal being used for both modes of operation.

The solid-state voltmeter section of the instrument employs a large amount of feedback to insure stability and flat frequency response from 5 cps to 3 mc. The voltmeter has 13 ranges in 10 db steps. Range is from 300µv to 300V rms full scale. The bandwidth is 5 cps to 3 mc for 1mV to 30V range, 5 cps to 500 kc for 100V to 300V range. The 300 µv range has bandwidth of 20 cps to 500 kc. The average-responding voltmeter is calibrated to the rms value of a sine wave.

The 332A is similar to 331A, but is provided with an amplitude modulation detector.