Cartridge Loading- Low output M/C

Your cautions are accepted. I've been thinking mil spec circular connectors and cables encased in grounded shields, or mono blocks bolted to the back of the speaker bases.

Interesting parallelism. I went from Magnepan to ESL-57's to Prodigies to 2905's. That's been an 'absorbing state' for 15 years now.

Thanks for providing the comprehensive simulations, Wyn.

Regarding:

Now 1000 pF. 0mdB at 20kHz, -32dB at 10MHz, 0.5dB peak at 1MHz.

Now 10nF. 10mdB at 20kHz, -52dB at 10MHz, 3dB peak at 400kHz.
Now 22nF. 20mdB at 20kHz, -59dB at 10MHz, 2.2dB peak at 270kHz.
Now 47nF. 27mdB at 20kHz, -65dB at 10MHz, 0.8dB peak at 147kHz.
Now 0.1uF. -12mdB at 20kHz, -72dB at 10MHz. No peaking, -3dB at 150kHz.

Am I correct in interpreting that these results are all with a 100 ohm load resistance?

If so, and given these results:

With the measured cartridge/minimum input cap (85pF) the response with a 47K R has a 29dB resonant peak at 4.3MHz and is -12dB at 10MHz.
With a 1k load it’s 4.2MHz and 9.5dB.
With 250 ohms it’s basically flat to 5MHz, with -14dB at 10MHz.
with 100 ohms it’s 1mdB down at 20kHz, with -17dB at 10MHz.

... It appears to me that these and the rest of your results are reasonably consistent with statements I, Atmasphere, and JCarr have made, and with what is illustrated in the plots provided in the post Jonathan linked to, that in the absence of a relatively heavy resistive load a large resonant peak will occur at an RF frequency, and (as can be predicted theoretically) at progressively lower frequencies as the amount of capacitance increases.

But as your simulations show, even if extremely large amounts of capacitance are present, e.g. 1,000 to 100,000 pf, a load resistance in the vicinity of 100 ohms will cause frequency response to be reasonably well behaved, at least for the particular cartridge parameters you chose.

However there is only one phono stage I am aware of which has an input capacitance within that very high range, that being the AcousTech PH-1, which in LOMC mode provides a load of 100 ohms in parallel with 10,000 pf. I believe that the great majority of other phono stages having active input stages have input capacitances in the area of perhaps 50 to 250 pf or so. I would expect that there are reasons for that.

And I would expect that in many cases those reasons, in addition to making it possible to provide a wide range of choices of resistive loading, are along the lines of what Jonathan has said in the post he linked to. Namely that heavy resistive loading "reduces the cartridge’s dynamics and resolution, and can also worsen tracking ability." As well as what I quoted him as saying in an earlier thread here, namely that "less capacitance allows the resistive load on the cartridge to be reduced, which will benefit dynamic range, resolution and transient impact."

Perhaps he or Ralph (Atmasphere) will elaborate on that, as they are much more expert in this area than I am.

Regards,
-- Al

What I don’t understand is why any of the purported effects of heavy resistive loading you state could be definitively true- certainly not on tracking which is demonstrably false based on IM tests on tracking performance that I have incidentally performed as a function of load. While mechanical impact does occur as a result of electrical load- there is some back emf necessarily generated by the signal current that affects the mechanical motion, but a quick back of the envelope calculation using Lenz's law and the 10uH cartridge suggests a 2 orders of magnitude difference between the generated signal and the back EMF for a 100 ohm load at 20kHz- certainly not enough to cause tracking issues I would think. As for the rest, well, take the Madake for instance- the resistive load that people (reviewers) claim is best literally varies by nearly four orders of magnitude! I load mine with 60 ohms (as do many users) and I find that the resolution and dynamics is excellent while maintaining a natural timbre, tonal balance and micro/macro dynamics while not creating the unnatural etched image that many "high resolution" MC cartridges produce.
In any case, I’ll have to research this to see what technical white papers or similar exist on the subject.

Wyn, I am glad that JCarr finally mentioned the fact that most LOMCs I know about have a much lower nominal inductance than the 0.5mH, on which you based your first set of calculations, and thank you for re-calculating your results based on more realistic values of inductance.  I also want to thank you, Al, JCarr, Ralph, and others for this civil and erudite discussion.  Such educational interchanges are all too rare on audiophile websites.  I only recently experimented with reducing the load on my LOMC cartridges, which is to say I am running them at 47K ohms routinely now.  I find the sonics to be more open and airy that way, and I feel no impulse to move back to the more typical 100R value.  I am sure my results have most to do with the nature of my particular phono stage, my downstream components, and my two ears,

Yes, it has been quite interesting and informative for neophytes like myself.
By the way, I constructed a model for the cartridge back EMF using Lenz's law and incorporated it into my simulations.
For those who are interested, the simplest version of the law is V(t)= -LdI/dt.
In this case the parameters can be measured (the LC100A meter from Ebay is a great way to do it) and the back EMF acts to oppose the voltage developed in the coil. The fractional change (attenuation) in the signal voltage is easy to calculate as it approx. equal to -L*2*pi*frequency of interest/Rload. So, it's inversely proportional to the load R and proportional to the frequency.
For example, for a 11.8uH cartridge, with a 100 ohm load the error at 20kHz is c. 1.5%.
The model measures the current through the coil and adds a correction of the form -k*s to the source voltage.
The effect can be seen both on the frequency response and on the transient response of the Phono preamp that I'm simulating.
Is anyone interested in this, or the simulation results?