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What’s All This Hassler Spice Stuff, Anyhow? (.PDF Download)

Oct. 5, 2018
What’s All This Hassler Spice Stuff, Anyhow? (.PDF Download)

Back in May 1995, Bob Pease wrote an article about the “hassler” circuit used by analog great Bob Widlar. The circuit sensed loud voices and would emit a near-ultrasonic squeal to dissuade further yelling or boisterous behavior. Widlar designed the circuit to quiet anyone yelling in his office. It also discouraged typing from a nearby secretary.

The actual circuit Widlar used is lost to history, but Pease postulated his own circuit. Several co-workers agreed that it was close in function to the Widlar circuit. The article is not online, but I found an old bootleg .pdf copy. The schematic was in the inimitable Pease hand-drawn style (Fig. 1). The heart of the circuit is a 22-kHz ultrasonic oscillator with a voltage-controlled frequency. When it senses loud audio at the input, the frequency slows down and drops into the range of hearing, making a nice annoying squealing sound.

1. Bob Pease designed this “hassler” circuit in 1995. It makes a squealing noise if someone talks too loudly.

As a consultant, I became a stickler for clear readable schematics, so I re-drew Pease’s circuit in my old Cadence OrCAD 9.2 (Fig. 2). I made sure the schematic flowed from left to right and top to bottom. Rather than wrapping it into a U-shape like Pease, I broke mine into two sections with an off-sheet port to connect the two halves. It fits on an A-sized sheet in portrait mode.

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