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RE: Long-term DBT example

Ah but... the kink is only in the "distortion" channel that's attenuated 34dB if set to 2%.

It's summed in with the main channel, though, so the combination must have the discontinuity in the derivative as well.

Edit: Update - I put the circuit into LTspice, using idealized op-amps (GBW=1GHz, DC OLG = 120 dB), and idealized diodes. I adjusted the pot to get the specified 2.5 percent THD at 1 kHz, assuming harmonics up to 20 (20 kHz). The pot value turned out to be 81.9k. Here is the spectrum.

Listed as harmonic number (1 = fundamental), relative dB

1 0.0
2 -32.2
4 -46.2
6 -53.6
8 -58.7
10 -62.6
12 -65.8
14 -68.5
16 -70.8
18 -72.9
20 -74.7

You can see that there's plenty of high-order harmonics. Also, the discontinuity in slope at the origin can be seen with a DC sweep.

Oh, I did verify that the distortion stayed at 2.5 percent for input voltages of 1 Volt peak and 0.01 Volts peak.

One other data point from the DC sweep:
Slope K1 for positive voltages = 0.939885
Slope K2 for negative voltages = 1.05464

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