>Another change is to the Zobel network resistance. This network is the series R/C circuit between the output of the amplifier and circuit common (ground). It provides a resistive load for >stability of the amplifier at higher frequencies when encountering inductive loads (e.g., the speaker and the speaker leads).

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The network also helps to stabilize the amplifier from oscillating when switching loads between speaker and headphones -- especially if there’s an open circuit condition at any moment between switching the loads.?

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Paul, W9AC