Boucherot cell
A Boucherot cell (or Zobel network) is an electronic filter, used in audio amplifiers to damp 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, usually placed across a load for stability. It is commonly seen in analog power amplifiers at the output of the driver stage, just before the output inductor. The speaker coil inductance of a loudspeaker generates a rising impedance, which is worsened by the output inductor generally found in analog power amplifiers; the cell is used to limit this impedance. The documentation for some power operation amplifiers suggests the use of a "Boucherot cell between outputs and ground or across the load". Additionally, Boucherot cells are sometimes used across the bass driver (and mid-range) of a speaker system, 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. Some loudspeaker crossover designs aim to stabilize impedance at high frequencies by including Zobel networks. (Wikipedia).
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