Class A Buffering the Correct Way

Here’s a simple way to force an opamp output stage to run in class A when used with a discrete buffer output stage – it takes just 1 resistor to provide a near constant current source load. Operating the opamp (and the output buffer stage) in class A dramatically reduces harmonics on the power rail and may offer improvements to the sound of your project.

You can download the two slides below as a PDF


3 responses to “Class A Buffering the Correct Way”

  1. Sergb says:

    simple and nice! thanks

  2. jacques rousseau says:

    very nice article.
    would it be possible to see how you implement
    the layout of your opamp class a module;
    I I’m interested in building one preamp
    with this topology,probably in instrumentation like
    balanced input.

    • Bonsai says:


      apologies for the late reply. The last time I built one of these was in 2010 IIRC so I don’t have anything to hand right now.

      The most important points regard layout are to keep it as compact as possible and to keep the junction of the feedback resistors as close to pin 2 of the opamp as possible – do nit run a long track from the junction to pin 2 as this invites noise problems. Secondly, keep the decoupling capacitors and their associated ground as close to the opamp as possible.



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