[sdiy] An Improved Sine Shaper Circuit

Donald Tillman don at till.com
Fri Apr 17 23:15:01 CEST 2020

On Apr 17, 2020, at 1:25 PM, René Schmitz <synth at schmitzbits.de> wrote:
> When I look at the Aries 317 or the Thomas Henry circuit I see that the triangle is not just a touch but very substantial in the output. (The TH circuit even returns almost all of the OTAs' output current into the resistor that connects to the triangle. (Its a high Z node, so if the OTA was shut off, it would be just fed through the triangle 100%)
> Clearly some form of zig-zagging is happening there too. Whether these circuits operate at an/your optimum is another matter.

Indeed, the Henry and Aries circuits do subtract a substantial amount of triangle.

So that's much more than "cusp cancellation". 

I don't know what their values are.  

I did find that if you don't get close to the 0.710 optimum beta value, then there's little improvement over the standard long tail pair.  With beta value of 0.710 the harmonics are down 76dB.  With a beta of 0.600, the harmonics are only down 44dB.

So the order of magnitude improvement happens at a golden point.

  -- Don
Donald Tillman, Palo Alto, California

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