Cartridge Loading- Low output M/C

OK. Thanks for defining what you mean. So lets look at power.
I ran a simulation and calculated the power dissipated in the cartridge series R and the load R and plotted what happened to the total power as the load cap is varied.
The voltage and current must be in phase for a resistor so power remains V^2/R. We know that the voltage across the load R is reduced as the cap is increased- after all, that’s the objective- so the load power must fall- but what about the series R? I calculated this and added it to the load power to get the total power.
So, back to the "real" case with a 11.8uH winding inductance , 16 ohm Rcart, 85pF load and 100 ohms. I set the input to 1v rms and calculated the total power in the two resistors =10*log(((voltageacrossRcart^2/16) +(voltageacrossloadr^2/100))
The power plot starts at -20.6dB at LF then falls by 3dB at 1.7MHz and by 18dB at 10MHz. No peak is present.
I then changed the cap to 0.1uF.
The power at 1kHz was -20.6dB, it peaks at -13dB at 150kHz , is 3dB off the peak at 87kHz and 320kHz, then falls monotonically by 25dB at 10MHz.
So we’re measuring 1/7 the bandwidth and a bit less than 6x the power in that bandwidth- which is, again, hardly surprising, so the power is more or less constant, but the total power at 10MHz is reduced and the load power at RF is hugely reduced, so isn’t that better?
Is the increase in power dissipation in the cartridge at supersonic but not RF frequencies problematic?
Darn! I wish I had some way of showing plots.

Wyn, I'm not claiming anything original here, except perhaps my anal-retentive dedication to costly devices!

Speaking of which - direct drive ESL. I have new generation Quads, which I opened up as soon as the warranty expired. I found a step-up transformer for each stator, cheap WW resistors and ceramic caps with their high dielectric constant. Obviously, all of these had to change.

As you seem to be an owner of ESL's, obviously you know that the step-up transformer tends to ring unless the input is coupled through a resistor. I changed the step-ups to a toroidal device which drove both stators, requiring an input resistor of about an ohm, which is a natural place for nichrome wire. Since I needed speaker cables anyway, I thought,"Why not use the nichrome wire for both purposes?"

Now I am thinking of high potential amps driving the stators directly, without any step-up device. I was wondering if you knew about HV transistors, and if you could save me some time and some angst with awful prototypes. That's all.

Well, I once was the proud owner of a couple of quads- the original ESL-57 and a pair of ESL-63s that I also pulled apart- their delay line/filter design to drive the annular segments was quite neat. However, I had serious reliability problems and I switched to Martin Logans and I've stayed with them ever since. I have Montis in the main audio room and a pair of venerable Prodigies in the home theater room and I've never had a problem with either of them.
Yes, I am aware of the fundamentals of their operation, but alas not the details so I really cannot help you out in this. Frankly, I'd be pretty leary about shipping the needed HV to the speaker from an external amp. Visions of lethally shocked dogs, maids, and kids spring into my mind. Having said that I believe that at one time Acoustat built ESLs without the transformer, instead using built in output transformer free tube amps

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