Thread: Tone Controls
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Old 14th May 2019, 6:30 am   #32
Radio Wrangler
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Default Re: Tone Controls

Those two circuits show the tone control as part of the feedback path which is OK. It varies the amount of feedback to impose control of gain versus frequency.

The FC38 diagram in post 23 is fundamentally different. The tone control elements (a full active Baxandall circuit in this case) is entirely in the forwards path, and there is flat feedback around the whole thing. If the tone control is used, the feedback system sees it as the same as unflatness in the power amp, and sets about improving (flattening) it. Essentially the feedback fights the tone control.

This is the difference between the effects of the forward path transfer function and the effects of the reverse path transfer function. Any text book should have the classic diagram and equation for a feedback system.

David
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