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You are here: Home / Mini Projects / Loudspeaker Thump Sound Eliminator Circuit

Loudspeaker Thump Sound Eliminator Circuit

Last Updated on May 21, 2021 by Swagatam 6 Comments

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While using amplifiers, we sometimes experience this very annoying thump sound, popping up in loudspeakers whenever the amplifier is switched ON or OFF. This normally happens with amplifiers that are of low quality or lack the feature of a thump eliminator circuit built-in in the amplifier.

The thump sound in loudspeakers can be not only annoying to the ears of the user, but it may be also equally detrimental to the speakers life, which might eventually at some point of time burn the speaker coils and cause a permanent damage to the loudspeakers.

In the proposed loudspeaker thump sound eliminator circuit, once installed and wired in an existing amplifier, will ensure that the loudspeakers connected with the amplifier never encounters this thump like pop sound.

Why the Thump Sound Happens

We know that every power amplifier involves a series capacitor connected with the loudspeaker. This series capacitor may be present either directly connected in series with the loudspeaker or connected across some other stage of the amplifier.

When power is switched ON, this capacitor causes an initial short circuit for the loudspeakers causing a loud pop sound to appear, which slowly decays away as the capacitor charges up fully.

The reverse happens when the amplifier is switched OFF, when the capacitor discharges through the loudspeaker again causing a loud thump sound through the speakers.

How the Circuit Works

As can be seen in the figure above, the loudspeaker thump sound eliminator circuit is actually built around a delay ON timer circuit. The transistor Q1 and the relay together with the capacitor C1 provides a delay of about 2 seconds before the relay is switched ON.

The relay can be seen wired with the loudspeakers, the amplifier and 10 ohm resistors.

The power to the transistor relay timer circuit is derived from the amplifier power supply itself.

When power to the amplifier is switched ON, the speaker remains disconnected initially since the relay does not switch ON due to the delay ON timer action. During this time, the capacitors inside the amplifier quickly charge through the 10 ohm resistor, connected with the N/C contacts of the relay. Once the initial delay is over, the transistor conducts and powers the relay, which in turn connects the loudspeaker with the amplifier.

The loudspeaker now makes no thumping or popping noise, since the amplifier capacitor are already charged up and the shorting of current to the speakers does not happen. In this way the thump noise is eliminated from the speakers.

The above working takes care of the amplifier switch ON issue, however when the amplifier is switched OFF, the transistor relay switches OFF quickly, preventing the amplifier capacitors from discharging through the loudspeakers. Instead, the relay contacts now connect them back to the 10 ohm resistors so that the internal capacitors can now discharge safely through the 10 ohm resistors. Due to this again the thump sound is eliminated from happening during the power switch OFF.

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About Swagatam

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials.
If you have any circuit related query, you may interact through comments, I'll be most happy to help!

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  1. chiroz says

    October 27, 2021 at 5:39 am

    can you teach me how to design a dc power supply

    Reply
    • Swagatam says

      October 27, 2021 at 1:08 pm

      Sure, the following article can help you:

      Designing Simple Power Supply Circuits

      Reply
  2. Carlos Alfredo says

    June 6, 2021 at 5:02 am

    Good night
    What is the power of the 10 ohm resistor
    Grateful for the attention

    Reply
    • Swagatam says

      June 6, 2021 at 9:04 am

      It can be a 5 watt resistor for amplifiers below 300 watt

      Reply
      • Carlos Alfredo says

        June 6, 2021 at 7:55 pm

        Good Morning
        Grateful for the answer

        Reply
        • Swagatam says

          June 6, 2021 at 8:07 pm

          You are most welcome!

          Reply

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