Boucherot cell

:"This article relates to loudspeaker driving. See Zobel network for a more general description of telecommunications useage"A boucherot cell (or Zobel network) is an electronic filter, used in audio amplifiers to dampen out high frequency oscillations that might occur in the absence of loads at high frequencies. Named after Paul Boucherot a boucherot cell typically consists of a resistor and capacitor in series, that is usually placed across a load, for stability.

Typical uses of boucherot cells

The documentation for power op amps, such as L272, suggest the use of a "boucherot cell between outputs and ground or across the load".

Additionally, boucherot cells are sometimes used across the tweeter of a speaker system [ [http://www.rane.com/par-b.html#Boucherot Rane Professional Audio Reference Home ] ] , in order to maintain a more constant driving point impedance as "seen" by a passive crossover. In this specific arrangement, the boucherot cell is sometimes also known as a Zobel network [ [http://www.rane.com/par-z.html#Zobel Rane Professional Audio Reference Home ] ] .

Zobel networks are used in audio amplifiers to dampen out high frequency oscillations that might occur in the absence of loads at high frequencies. It is the commonly seen series resistor-capacitor combination located directly at the output of the driver stage, just before the output inductor (in analog power amplifiers). Typical values are 5-10 ohms in series with 0.1 microfarads. The network limits the rising impedance of a loudspeaker due to the speaker coil inductance. The output inductor found in most analog power amplifiers used to disconnect the load at high frequencies further aggravates this phenomenon.

Loudspeakers

Some loudspeaker crossover designs include Zobel networks wired across the tweeter (high frequency) driver to compensate for the rise in impedance at high frequencies due to the inductance of the voice coil. The goal is to try to keep the load seen by the crossover circuitry as resistive as possible. [Bell Labs Journal: Zobel, O. J., "Theory and Design of Uniform and Composite Electric Wave Filters," Bell Sys. Tech. J., Vol. 2, pp. 1-46, Jan 1923.] [ST, [http://www.st.com/stonline/products/literature/ds/1321.pdf LOW DROP DUAL POWER OPERATION AMPLIFIERS] , July 2003, Top of Page 5, right column.]

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