Cartridge Loading- Low output M/C

Hi Wyn,

Thanks for providing the excellent and thought-provoking analysis. I see no flaws in it as far as it goes. And in fact the manual for the OP’s phono stage states that the higher capacitance setting (570 pf) can sometimes be beneficial with respect to "interference rejection," when used with LOMCs.


However I believe what underlies the differing perspectives between your analysis and what I, Atmasphere, and JCarr have maintained is that while your analysis focuses on rejection of RFI per se, as reflected in your choice of 10 MHz in the analysis, I and the others have focused on energy that may be generated by the cartridge itself, at and near the resonant frequency. Not directly in response to musical information, which is presumably not present at frequencies of hundreds of kHz and above, but rather in response to "surface noise," tics and pops, and other causes of unwanted high frequency modulation of the output of the cartridge. Or (and I’m just speculating here) perhaps as a result of upper order harmonic distortion components that may be generated by the cartridge in response to musical information at lower frequencies.


As Atmasphere stated in a post in this thread on 5-21-2018:

... the cartridge inductance combined with the tone arm cable capacitance forms a tuned RF circuit- which is energized by the cartridge signal. It can be over 30 db higher than the phono signal- thats about 1000x more powerful!

Note the words "which is energized by the cartridge signal."

I guess the bottom line, though, is that as is usual in audio there are many complexities and competing tradeoffs involved, as well as many system dependencies, and consequently there are multiple paths to an optimal setup, and multiple paths to setups that are less than optimal to varying degrees.

And speaking of complexities and competing tradeoffs, your mention of SUTs certainly brings many more into play. As I’m sure you realize, optimal loading with a SUT will usually be different than when a cartridge is driving an active circuit, in part because of the need to optimize loading of the transformer itself, to minimize ringing and resonances. Another consideration being that capacitance that is present on the secondary side of the SUT will be presented to the cartridge multiplied by the square of the turns ratio.

BTW, was the AD797 one of the integrated circuits you mentioned having designed? If so, or even if they were anything comparable, I’m truly impressed!

Best regards,
-- Al

P.S: @terry9 ;-)

No, I did not design the AD797. That was Scott Wurcer- a colleague at ADI and, incidentally, for whatever it's worth, also an ADI design fellow. However, I know the design quite well.
He and I were colleagues in the opamp group in the 80s. He focused on high performance relatively low frequency opamps such as the AD712 and then the AD797, amongst others.
I focused on high performance high speed amps like the AD843, 845 (at one point an audio darling), 846 (also a transimpedance design with some very interesting design aspects that I gave an ISSCC paper on) etc. etc. mostly using a complementary bipolar process that I helped develop that I believe was also used in the AD797. I also did things like designing the FET based AD736/737 RMS-DC converter and others.
I moved on to more RF, disk drive read/write, GSM, CDMA etc. transceivers, signal processing, PLL and DSP designs. 
Anyway, what the heck does "cartridge energy" actually mean?
It's an electromagnetic transducer that I grant you has a fair degree of non linearity (which is one of the reasons I like the Madake- it's quite low distortion for a cartridge and why I have ML Monti loudspeakers as most loudspeakers have far too much distortion for my taste) so it generates a voltage and has an output impedance.
I can vouch that the Miyajima cartridges respond to ticks and pops just about as you would expect based on their frequency response and the amplitude of the signal generated, so no alternative explanations are necessary. Are you perhaps stating that the increased current generated by the lower resistive load increases distortion? If so, I can say that I believe that it's not true for the Madake as I've measured IM and harmonic distortion under varying load conditions (Ah the joys of test records)- and they are really sensitive to cartridge alignment but not that I can tell, to  load.
And yes, I'm well aware of the SUT impedance transformations- and I also model them, although imperfectly, in LTspice, which uses calls to set up the parameters.  This can be quite insightful, for example are you aware of the LF response sensitivity to winding inductance? 
One of the "joys" of being an IC designer is the compulsion to measure/model everything! However, once the skills are developed it's relatively easy to do as long as someone else has done the hard work of producing suitable models to use.
Constructing an electrical model for the Madake was fraught with concern as using my own meters to measure the capacitance and inductance was anxiety producing.
Then when I plugged the parameters into the simulation and compared against my measured output I realized that the actual response had precious little to do with the electrical characteristics and everything to do with the mechanical resonances.
And so, the journey began...

Are you perhaps stating that the increased current generated by the lower resistive load increases distortion?

No, I was not saying that or implying that. And for that matter I have no particular knowledge of how the distortion performance of phono cartridges tends to vary as a function of load impedance.

Regards,
-- Al

Thank you, Wyn. Food for thought - or rather, food for experiment. Another pole means another stage and another pair of complementary devices, so the trade-off is obvious. But next is the amplifiers' turn, so it will have to wait!

Thanks again for your insights.

Dear @krelldog : I posted several times in this thread each one ignorance levels where some people has higher when other lower in this specific subject but additional to that there are all over the world ignorants that additional are in the stupidity are because can't understand that or those or anything on audio.

My attitude is always try to help for any one ( including me. ) trys to low those ignorance levels but I always ignore stupid persons because will never learn.

R.