Phono rig capacitance

... Can you please give some input on the basic structure.... I tried to follow Jcarr's model, but in the end I am still not sure why when modeling a wire connecting devices you would model the RCL in series or in parallel, and in what order you place the RCL for the wire....

As I indicated near the end of my last post, your model looks good to me aside from the SUT issues.

For the cables, R and L are in series, and C is in parallel. Representing these parameters as "lumped" elements, with the capacitance first in the chain, as you have done, rather than as a great many separate elements representing their distribution along the length of the cable, I believe is a reasonable approximation at frequencies of interest.

Regarding the SUT model, the inductances of each of the two windings will probably not be in proportion to the square of the turns ratio, and may be directly proportional to the turns ratio itself (depending on a number of variables). And more significantly, if it is not clear, the inductances that should be represented are not the inductances that each winding would have if it were divorced from the other (i.e., their self-inductance). What should be represented, as I mentioned, is "leakage inductance," in series, and perhaps also a parallel inductance (and resistance). I don't know what values would be reasonably typical for those parameters for typical SUTs.

Also, Lew's comments are good ones IMO. Jonathan's emphasis on minimizing cable capacitance on the secondary side of the SUT should also be kept in mind, of course.

Regards,
-- Al

P.S. to my previous post: Regarding "leakage inductance," see this Wikipedia writeup.

Regards,
-- Al

Hi,

According to this link the:
"...Remember,
the inductance is proportional to the
square of the turns ratio. In the ex ample above, a turns ratio of 1:3 gives a 1:9 inductance ratio..."

they they proceed to use 100uH : 900 uH.

I have not even got the slightest clue where to get the actual figures for the SUTs, as none of them publish this information. I suppose I can try to email cinemag, Jensen etc... to see if I can get it.

http://cds.linear.com/docs/en/lt-journal/LTMag-V16N3-23-LTspice_Transformers-MikeEngelhardt.pdf

Now, I followed this guide to implement the SUT. Worth repeating: I know very VERY little about electrical engineering. However, in the current model as I raise Capacitance massively on either side of the SUT is makes NO difference to the frequency plot. Also the Freq plot is offside by over -50db...as it should be reading +20 after going through the SUT. Hence Why I think there may still be something off. I dont know enough EE to figure out what the "something" is. Please experts, lend a helping hand, CALLING ALL EXPERTS PLEASE!

It would be great if I could attach the model so you can open it in your own software without re-sketching it. If you know of a way please tell me, I cant seem to attach files on audiogon.

I tweaked the model, after reading another paper on tranmission lines etc.. I found a model that made sense and demonstrated the correct db gain and presented a familiar looking bode plot. I think this lumped model may be correct, or at least "better".

See the link
http://postimg.org/image/dgyazcfhj/

I tested this model with some extreme values, and compared to the baseline case outlined in Jcars white paper. I used the specs from the Mogami 2549 out to as much as 20 feet worth of RCL, tried changing the cartrdige parameters for impedance up to 50 Ohms and 500 Uh etc...

The only changes I have noticed in the response curve are in the ultrasonic peak shape and neighborhood, though this activity occurred far away from the audible band (100K or more). The Subsonic roll off was very slightly affected and was still very low (<15Hz) across the values used. Of course this is under the "Perfect" transformer assumption. So this model is showing that a cable with the characteristics of the 2549 is capable of reproducing the signal without an drastic changes to the frequency response in an MC Phono rig, provided that the parameters of the cable are "reasonable" and inline with what most people would use anyways.

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