"
... There is no horizontal scale ..."
I see "LOG Frequency" at the bottom of the FFT Graph when I scroll down.
"
... model of the transformer ..."
There is no transformer, only Op-Amps & R-C filters.
"
... model of the load ..."
The Bubba Sine Wave output is taken from the Low Impedance output of the Op-Amp at the Final (5th) Stage.
The Load will be High-Impedance Inputs of two other Op-Amp circuits.
The next Stages (Absolute Value & Zero Cross) are not designed, yet.
I can upload asc file later tonight.
I used this bubba schematic on page 5 as my starting point ...
https://www.electro-tech-online.com/custompdfs/2009/12/aug_07.pdf
But I added a 5th Op-Amp (Unity Gain) between
the "Cosine" R-C stage and the next "Rg-Rf" Stage.
This way, no R-C circuit was "loaded" by the next stage.
I took my Bubba Sine Wave from the output of this new 5th Op-Amp.
It is very clean when compared to the Sine Wave of the LTSpice Component.
I changed the R-C to 25.5k & 0.1uf = 60hz, if I remember right?
I had read some articles about computing %THD from FFT Graphs.
But their FFT Graphs only had 6 clean spikes at the Harmonic Frequencies
not the squiggly FFT graph I get from LTSpice.