The paper describes a D.C. chopper stabilized amplifier which is being used to amplify seismic signals from a Willmore S.P. geophone to a level suitable for direct recording on a 0-1 milliamp pen recorder. The over-all magnification of the system is approximately 10,000, while the amplification of the D.C. amplifier is 60 volts per microamp. The frequency response of the amplifier is D.C. to 75 cycles per sec. (3 d.b. down).

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