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Removing the DC Thump from Audio Circuits

Removing the DC Thump from Audio Circuits

Most audio outputs have some standing DC voltage which is separated by a capacitor. The capacitor will block this DC voltage while allowing the AC or audio to pass. Audio components using transformer coupling are not affected.
Most audio outputs have some standing DC voltage which is separated by a capacitor. The capacitor will block this DC voltage while allowing the AC or audio to pass. Audio components using transformer coupling are not affected. The input to an amplifier may have a capacitive input or just a volume control. When switching inputs, charge is transferred through the switch as the input or output capacitors or both reach a state of equilibrium. This takes only a fraction of a second and what you hear is the annoying dc thump.



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At input 1, there is a standing dc voltage on the emitter of the transistor in system A. This is isolated by the 47u capacitor. The capacitor will either be discharged or partly charged. When the rotary switch is turned to position 1 a click will be heard as the capacitor charges through the switch and volume control on the following amplifier. A similar condition appears at switch position 3. System A represents part of a preamp while system B represents the output of an amplifier. What can be done to prevent this?

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