565 - DL Instruments Preamplifiers

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Technical Specifications

High end frequency limit

Transformer mode: 60 dB

Noise Figure

Extra Specifications
Ultra Low Noise Transformer Coupled Voltage Preamplifier

Product Description

The 565 is operable in two modes. In the direct mode, it yields 40 dB of gain with medium impedance performance - similar to the model 566 voltage preamplifier. In the transformer mode, it provides exceptional noise performance (equivalent to the Johnson thermal noise of a 1.4 ohm resistor at 300 degrees K) by switching in a 20 dB impedance matching transformer ahead of the amplifier stage. Its superior magnetic design also yields very wide bandwidth for source impedances of 10 ohm or lower.

Caution: The 565 cannot tolerate dc voltage on its transformer input in excess of ± 10 millivolts. For ac inputs below 50 Hz riding on the dc bias, the allowable dc level for less than 5% gain error will decrease linearly with frequency. Thus for a 5 Hz signal, only 1 mV of dc input bias would be allowable.

The input transformer is torroidally wound to render it insensitive to stray magnetic fields. Additionally, it is completely encased in mu-metal to shield against magnetic pickup. The input transformer also incorporates a conductive shield to prevent capacitive coupling of common mode interference from the input winding to the secondary winding. The aluminum case of the 565 affords a further shielding effect against electric fields.