Bias setting with a scope. Why or why not!

[dragonbat13]

Is there any reason folks do or don't adjust bias with an oscilloscope, adjusting out the crossover notch?

I was just wondering why I never hear of it being done this way.

[LOUDthud]

People that bias high end Stereo amps will use a scope because the goal is minimum THD. For Guitar amps, not so much.

[martin manning]

R Aiken has written about it here: https://www.aikenamps.com/index.php/cro ... be-avoided

[Stevem]

That procedure for setting what amounts to the minimum bias may not provide the liked ratio of output stage clipping and preamp clipping when driving a loud volume level to your ears.

[wpaulvogel]

If you have a scope, it’s not a bad idea to view the waveform during bias adjustment. If you can achieve no crossover notch at full clean rms output before a 70% bias dissipation setting, I’d say that’s the perfect bias point. It’s not critical to view the waveform but with the tool available, why not check to see what it looks like. On high voltage amps like old Plexi’s, it’s hard to bias out the notch and I like to see what it takes and make a decision about whether to push the dissipation or if it’s just to far away to reach. I always scope just for assurance.