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Amplifier running idle

Discussion in 'audio' started by Allaboutmusic, Mar 25, 2020 at 5:04 PM.

  1. realysm42

    realysm42 reMember

    What is it about running an amp at 1/3 that makes them overheat? Is this universal, regardless of amp class?

    I’ve noticed Stereophile do it as part of their amp reviews (in the measurement section) and amps have failed as a result.
  2. Allaboutmusic

    Allaboutmusic pfm Member

    Would you switch it on and off throughout the day? I tend to leave on if I am listening intermittently but switch off if going out and always when going to bed.
  3. S-Man

    S-Man Kinkless Tetrode Admirer

    It is mainly for class (A)B amps.
    There is a worst case power dissipation at about 1/3rd of the maximum RMS output power. (theoretically it's at about 40%, but rail sag will affect this is practice) At higher output power the instantaneous dissipation in the o/p transistors actually goes down because the losses are related to the supply voltage minus the output voltage X the output current.

    There really is no need for amps to be able to handle this. The increase in dissipation due to awkward loads is more than offset by the decrease resulting from the crest factor (dynamic range) of music.
    Arkless Electronics likes this.
  4. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Heat at idle is a combination of heat from the transformer (usually not much), rectifiers (again usually not much) any being generated by voltage regulators, dissipation of resistors throughout the unit (often negligible) and usually the main source is the quiescent dissipation of the output stage.

    I would just leave it on all day if you are going to be using for much of the time. Common sense applies here.... don't leave it on all day cos you wish to play music for 20 mins!

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