John Dunn

Merrick, N.Y.

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Shunt Capacitance Can Suppress Magnetic Headset Oscillation

By John Dunn, September 02, 2002

The nominal impedance of a magnetic headset isn't necessarily a good description of its actual impedance as a function of frequency. A headset's fairly complex equivalent circuit may even lead to parasitic oscillations in a driving amplifier. But...
Resistor L-network Matches Impedances

By John Dunn, June 13, 1994

A resistor L-network is used as an impedance-matching circuit between two transmission lines of differing characteristic impedances. With the acceptance of resistive loss, a nominal 1:1 VSWR can be maintained on each line.
Mimicry Finds Defective Buried Components

By John Dunn, July 09, 1992

By using a mimic test setup, you can locate a defective component in a potted assembly without opening up the device.
Make Polystable Memory Elements

By John Dunn, March 19, 1992

A tristable memory element can be created by connecting three two-input NAND gates such that each gate's output goes to an input on the other two. A quadristable memory element uses four three-input NAND gates.
Test High-Voltage Capacitors Safely

By John Dunn, March 05, 1992

Using a Bertan 205B-20R high-voltage power supply or equivalent to deliver a very pure dc input, this test circuit evaluates capacitors rated up to 20 kV.
AC Amplifier Passes Low Frequencies

By John Dunn, January 09, 1992

By basing an amplifier on a negative-resistance converter instead of input bootstrapping, you can build a device with a very low cutoff frequency, a modest-sized capacitor, and independently adjustable gain and input resistance.
Relay Selects Between Two LEDs

By John Dunn, January 31, 1991

This circuit switches between two LEDs on a front-panel display using only an SPST relay. A current source can be inserted to keep equal brightness for both LEDs.