Sure you have got distortion on the sim .You You will get it in real life .Try Try making the input volts 10 volts to reduce diode effects .If If this helps then place a DCDC voltage source in series with your AC generator.Experiment Experiment with a start value of say half a volt .Most Most AM detectors are prebiasedpre-biased to remove some diode nonlinearity .Then Then reduce the RC time constant accepting more ripple .Now Now you can postfilterpost-filter to get the ripple down to an acceptable level .Often a Often an RC section is adequate .I I have used fullwavefull-wave bridge to getto get low 2F2F ripple that is easier to postfilter post-filter.I I have benched a germanium prebiased fullwavepre-biased full-wave bridge that performs well .If If you have spice models for these then you could try . NowNow things can get worse when modulation % is increased like 90% .When When you do this on the sim you will have to do more optimisationoptimization.