Looks like you've made some progress. Good!
I'm surprised that relocating the connections of the cable capacitance elements in the model (together with the minor changes you've made in some of the capacitance values) had such a profound impact on the results. I don't know how to explain that.
Also, keep in mind that even though the response peak is way above the range of audible frequencies, its amplitude and frequency are nevertheless important considerations, which stand a good chance of being audibly significant. Again, see Jonathan's post in another thread that I linked to earlier.
Regarding the transformer model, I read through the "Using Transformers in LTspice/SwitcherCAD III" paper you linked to, and I also looked at some of the literature on LTSpice at the linear.com website. Their simulation is done differently than what I was envisioning when I provided my earlier comments. I was envisioning that the transformer would be modeled as an ideal transformer (k = 1; infinite self-inductance of the windings; zero leakage inductance, etc.) in combination with external circuit elements representing its non-ideal characteristics. They are modeling it as a single non-ideal element. So take that into account when considering my earlier comments.
I would expect either approach to yield good results, IF the parameter values are suitably chosen. And again, I have no knowledge of what the appropriate values might be for a typical SUT. Also, you might try re-running your simulation with k values of say 0.9, 0.8, etc., to see how sensitive the results are to that value. k = 1 corresponds to zero leakage inductance, which of course is not possible with a real world transformer.
Finally, a note of caution. It appears that despite statements indicating that LTspice/SwitcherCAD III (or "LTSpice IV" which is what is available for download at their website) is/are "general purpose," it appears that their program is oriented toward facilitating analysis of switching power supplies. As stated in one of their papers, "LTspice is a high performance SPICE simulator, schematic capture and waveform viewer designed to speed the process of power supply design. LTspice adds enhancements and models to SPICE, significantly reducing simulation time compared to typical SPICE simulators, allowing one to view waveforms for most switching regulators in minutes compared to hours for other SPICE simulators." And of course the designs of power supply transformers and cartridge stepup transformers are vastly different.
Regards,
-- Al
I'm surprised that relocating the connections of the cable capacitance elements in the model (together with the minor changes you've made in some of the capacitance values) had such a profound impact on the results. I don't know how to explain that.
Also, keep in mind that even though the response peak is way above the range of audible frequencies, its amplitude and frequency are nevertheless important considerations, which stand a good chance of being audibly significant. Again, see Jonathan's post in another thread that I linked to earlier.
Regarding the transformer model, I read through the "Using Transformers in LTspice/SwitcherCAD III" paper you linked to, and I also looked at some of the literature on LTSpice at the linear.com website. Their simulation is done differently than what I was envisioning when I provided my earlier comments. I was envisioning that the transformer would be modeled as an ideal transformer (k = 1; infinite self-inductance of the windings; zero leakage inductance, etc.) in combination with external circuit elements representing its non-ideal characteristics. They are modeling it as a single non-ideal element. So take that into account when considering my earlier comments.
I would expect either approach to yield good results, IF the parameter values are suitably chosen. And again, I have no knowledge of what the appropriate values might be for a typical SUT. Also, you might try re-running your simulation with k values of say 0.9, 0.8, etc., to see how sensitive the results are to that value. k = 1 corresponds to zero leakage inductance, which of course is not possible with a real world transformer.
Finally, a note of caution. It appears that despite statements indicating that LTspice/SwitcherCAD III (or "LTSpice IV" which is what is available for download at their website) is/are "general purpose," it appears that their program is oriented toward facilitating analysis of switching power supplies. As stated in one of their papers, "LTspice is a high performance SPICE simulator, schematic capture and waveform viewer designed to speed the process of power supply design. LTspice adds enhancements and models to SPICE, significantly reducing simulation time compared to typical SPICE simulators, allowing one to view waveforms for most switching regulators in minutes compared to hours for other SPICE simulators." And of course the designs of power supply transformers and cartridge stepup transformers are vastly different.
Regards,
-- Al