Cartridge Loading.....Part II

Dear friends : For some of you that read for the first time the Wyn posts here next I pasted what he posted several years ago in other cartridge loading thread:

 

"" 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. ""

 

and here somerthing that he forgot to mention and that comes in that " old " thread that shows that that " myth " of tracking problems due to cartridge loading changes is a lie and nothing more:

 

""" 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. """

 

 

R.

@rauliruegas ,Don't worry friend, there is now a front panel switch that allows you to switch back and forth, no more jumpers. The Phono Stage has a 5 MHz bandwidth. I did order an ultra accurate RIAA board but I am already set up to do digital RIAA correction. 

Who came up with the thought that cartridge loading affected tracking? That is rather silly. Once you get to an extremely low impedance input there is less back EMF for certain. I have seen oscilloscope tracings showing this. I am not an electronics engineer. I can only rely on what I read and see and have to assume it is not marketing BS. I sort of doubt Rob Robinson is the type of guy to BS his customers.   

Who came up with the thought that cartridge loading affected tracking? That is rather silly.

A guy named Lenz observed and documented the underlying concept and I'd hesitate to call his work silly.  Now extrapolating his work to cartridge loading is interesting.  Moncrief showed decidedly different IMD results between the same cartridge lightly and heavily loaded.  While I have not been able to replicate his results perfectly, I have seen several areas where loading effects the measured behavior of a MC cartridge. 

Stepping back and looking at the big picture One has to ask "What causes IMD sidebands from the record groove needle interface?"  The only answer I can come up with is mistracking.  A number of tracking ability tests exist.   Tests like the Audio Obstacle Course use recored music with increasing levels of one selected instrument and the user can judge where mistracking happens.  This is the closest we can come to a real world example but it is important to understand the results are subjective which makes the results unique and hard to relate to others.  The other approach as used on the Shure TTR103 and the CBS STR110-112 is more scientific and requires the use of two tones typically 400hz and 4kHz  and an intermodulation distortion measurement.  Here is the blurb from CBS:

The two things that jump out at me in the above are the use of the phrases "Instantaneous force" and "tracking distortion" both of which seem to be directly related to the topic at hand.  The last bit about other system nonlinearities causing IMD is valid but outside the realm of the variable being tested here. (tracking force)  If we agree that the load will as ralph states above:

cause the cantilever to be harder to move (stiffer)

It seems fair to follow up with the premise that this can also effect tracking ability.  It is important to note that the extreme and clear results given by Moncrief do represent the two extremes where Rcart<<Rload and Rcart>>Rload which just happens to be the exact case of the ideal current mode vs. voltage mode input stage. 

dave

Dear @mijostyn : Over several forums that person is atmasphere, yes silly.

 

@intactaudio , " The only answer I can come up with is mistracking. "

 

All cartridges no matter what has a mistracking issues always and in every LP recording.

Sometimes and depending of the room/system resolution levels and the accuracy of the cartridge/tonearm alignment and set up we can be aware of some of those " mistracking " and normally we don’t.

 

In the other cartridge loading thread other gentleman and I with out been in touch made tests using the same cartridge making changes on load. The cartridge was a non very good tracker: Denon 103 and both of us in different room/systems and different loads can’t fin out any difference in what we were listening due to load changes.

 

In that thread I named some of the over 20+ test LPs I own where are those 2 you named here.

 

Wyn proved that loading does not affects the tracking cartridge abilities and JC says the same and we audiophiles tested and confirm it. What exist always is IMD issues but not for loading additional mistracking.

 

In the other side, think what you need to change the cartridge tracking ability with the effect to have higher mistracking levels ( everything the same ) and you will find that the parameter that needs to be changed is the compliance ( of course that VTF or AZ or VTA can do it too but everything the same compliance is the one. ) in the cartridge and for in true can exist a higher levels of mistracking maybe you need to change say 15cu in the cartridge to around 8cu-10cu ( and in this non-existent hypothetical example it will change too the tonearm/cartridge resonance frequency. ) and certainly load changes can’t do that not even can makes that compliance goes down from 18cu to 17.8 cu.

Loading does not affect tracking/compliance in cartridges and certainly not FR that as said JC: " that’s bogus.

Now, one thing is try to change compliance in static status and the other during playback because in playback all the stylustip/cantilever forces that provoque the spining of the LP grooves friction against the stylus ti are enormous/gigantic for any radical change of loading can disturb it and remember that the stylus tip is in continuous " jumping "/loosing contact with the LP surface. Loading does not change all those.

Why the changes in measured IMD by PM? for other reasons but tracking issues. Btw, please makes this test several times: track the same LP grooves and measured 4 times in a raw and you will see that measures you took are different even that made with the same test grooves.

 

R.

 

 

 

 

 

Those tests with the same loading and you will see as I said that measured not the same but with tiny differences.

 

R.