Are all amplifier watts the same?

January 11, 2019
 by Paul McGowan

2 comments on “Are all amplifier watts the same?”

  1. Paul,

    You are not alone in struggling to explain the heat generation created with Class A amplification.

    I work on aerospace flight controls which use both electronics and hydraulics. Over the years I have discovered that when explaining electrical power characteristics a direct comparison with hydraulic power characteristics helps people visualize the physics. They share the same basic equations;

    Current X Voltage = Elec Power
    Flow X Pressure = Hyd Power

    So imagine a Class A amplifier as a servo valve (like a vacuum tube or transistor) in a hydraulic system. To regulate a constant supply pressure (like voltage) a pressure relief valve dumps excess flow back to return (ground).

    When the servovalve is closed all flow exits through the pressure relief valve. Since none of the flow is doing any work, all power consumed is converted to heat. If the servovalve is commanded wide open and all available flow is used to do perform work, negligible heat is generated.

    In high-efficiency hydraulic systems (like Class D amps) we use a special pump that regulates pressure but generates only the flow required by demand. This eliminates almost all waste heat.

    I enjoy your videos daily.

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