Cartridge Loading.....Part II

On the subject of phono input impedance as it relates to the discussion between Atma-sphere and Intact Audio, one should also keep in mind that every "current drive" phono stage seems to be a bit different from every other "current drive" phono stage, at least on the subject of input impedance.  Most advertised "current drive" phono stages do have a finite input impedance greater than zero, whether that is virtual zero or whatever.  A couple of years ago, I looked at 4-5 different products and the range of measurable input Z was from a few ohms up to as much as 20 ohms.  A unit with a real 2-ohm input Z will probably react differently to a LOMC with an internal resistance of from 2 to 10 ohms than a unit with a 20-ohm input Z, current, voltage or whatever.  The water gets really muddy.  They want to dumb it down for us consumers.

The topic of this thread is cartridge loading and it only makes sense to look at it from the two terminal perspective of the cartridge without concern of the "technology" used to provide that load.   There are two basic extremes of operation of a cartridge.  It can operate as a current generator where the load value is << the cartridge internal impedance or it can operate as a voltage generator where the load value is >> than the cartridge internal impedance.  There is also a fairly grey area inbetween these two extremes where the load value is ≈ the cartridge impedance.  For this basic discussion I think the two extremes need to conceptually be looked at from the ideal with respect to how the cartridge converts a mechanical movement into an electrical signal.  Since it is the source to load relationship that dictates whether a cartridge generates current or voltage it becomes important to determine if changing the load causes any mechanical or electrical change to the behavior of a cartridge.  

 

When operating as a voltage generator the load can easily be modified over a fairly wide range and still maintain the basic principles of operation.  I think most will agree that loads  of 10X the cartridge impedance and up have a cartridge operating squarely in the voltage realm and people will start to cry foul as your load approaches  the cartridge internal Z.  This doesn't have anything to do with actual cartridge behavior and everything to do with the type of amplification that follows.  For voltage amplification the unique case where Rsource=Rload nets a 6dB voltage loss and in the case of microvolt level signals that is huge.  Going to the case where Rload is 1/4 that of Rsource the voltage loss will be 18dB which immediately disqualifies that as an option for many.  The problem with that categoric disqualification is that you are trying to make a cartridge operate as a source of current into a voltage amplifier. The problem has nothing to do with the actual load and everything to do with using the wrong tool for the job.  If the goal is to actually load the cartridge with 1/4 the internal impedance then that load should simply be provided by a current amplifier.  If we want to discuss the effects of loading on the behavior of the cartridge we have to assume that the appropriate type of amplification is used.

The first question that needs to be addressed is in a perfect world with ideal amplification, will a 40Ω cartridge sound the same into a 5Ω load as a 47kΩ load? 

 

The first question that needs to be addressed is in a perfect world with ideal amplification, will a 40Ω cartridge sound the same into a 5Ω load as a 47kΩ load? 

Right up to this point I was in agreement with the prior text of this post. With this question we can safely say the answer is 'No.', assuming that the perfect amplification is voltage amplification. The question cannot be answered at all if current amplification is used.

If that is a static load (IOW, a resistor) then the cartridge will be making 4 orders of magnitude more work! That work has to come from somewhere, otherwise a new branch of physics is created 😉

So it will certainly cause the cantilever to be harder to move (stiffer) and that will affect how the cartridge 'sounds'. It won't affect the bandwidth of the coil in the cartridge at all- but will have an enormous affect on the mechanical aspect as the coil will have become a significant load with 5 Ohms loading it in turn. Also, the output level will be considerably decreased!

The question cannot be answered at all if current amplification is used.

Why not?  Consider the case to be an ideal current amp with the appropriate series resistance added so the input impedance is 5Ω.   In this gedanken world the ideal voltage amp and the ideal current amp sound identical.

If we can agree on this then we can get to the question I am really curious about and that is....  How much of the sound of current amps vs. voltage amps is simply due to the radically different load the cartridge sees? 

 

A simple experiment I have been contemplating playing with is to compare the loading extremes is to use a 1:10 sut loaded with 300kΩ to load an 8Ω cartridge with  3K.   Then take the same cartridge and feed a 1:20 and apply an 8Ω resistor as a load directly to the cartridge.  The extra 6dB of gain from the increased turns ratio will be offset by the ~6dB loss of the cartridge being loaded with its internal impedance.  One could even take it a step further and try a 1:40 with a 4Ω parallel load to see the sonic effects of the extremes.  

dave

 

Why not?  Consider the case to be an ideal current amp with the appropriate series resistance added so the input impedance is 5Ω.   In this gedanken world the ideal voltage amp and the ideal current amp sound identical.

It seems to me that you are still conflating virtual ground and actual ground as the same thing! As I said before this leads to confusion.

So the 'Why not?' is the same as before: Because that 5 Ohms is a virtual 5 Ohms instead of a real 5 Ohms. The cartridge is not loaded at an actual 5 Ohms. 'Virtual Ground', again, is opamp parlance for a point in the circuit that exists at the same potential as ground but isn't actually ground.

I recommend that you read up on opamp operation since this seems to be the hanging point. Here's a short tutorial opamp virtual ground.

If you don't want to do that, just keep in mind that 'virtual ground' isn't the same as actual ground. So the cartridge would not be loaded at an actual 5 Ohms even though the virtual ground is 5 Ohms.

Ralph, two questions:

(1) what if the input device is a discrete transistor or a tube, not an op amp? 
(2) the only way I can imagine two points separated by 5 ohms but at the same potential is if and when there is no current flowing. How does that work in this case?

Thx

(1) what if the input device is a discrete transistor or a tube, not an op amp?

@lewm 

Then there won’t be a virtual ground. So right away its a voltage amplifier not a current amplifier.

(2) the only way I can imagine two points separated by 5 ohms but at the same potential is if and when there is no current flowing. How does that work in this case?

Opamps have nearly infinite gain when open loop; the feedback resistor and the input resistor thus define the gain of the circuit and the virtual ground is formed at the intersection of the input resistor and the feedback resistor (see my prior posts for more information).

There is no connection between actual ground and virtual ground; the latter is created as a result of the feedback meeting the input signal. So there isn’t (as in the case of 5 Ohms) 5 Ohms between the ground and the virtual ground. In fact the actual impedance is much higher.

The ’0 Ohms’ value you see in so many phono sections that have transimpedance inputs probably isn’t helping people to understand what is going on. That value is probably the marketing department talking since they probably didn’t understand what a virtual ground is.

The tricky bit is that in a transimpedance input, the cartridge itself is the input resistor. This means that the actual impedance load on the cartridge varies with the impedance of the cartridge itself- and with it, the gain of the circuit. As I pointed out earlier, the lower the impedance of the cartridge the higher the gain of the circuit.

 

Ralph, you wrote, "The '0 Ohms' value you see in so many phono sections that have transimpedance inputs probably isn't helping people to understand what is going on. That value is probably the marketing department talking since they probably didn't understand what a virtual ground is."

I have been complaining about that on this forum over and over again.  Only be direct questioning can one find out what the input impedance of these "current driven" phono stages actually is, and it's typically from a few ohms in the best case to as high as 20 ohms.  Even the term "transimpedance" is a marketing ploy.  Almost as bad as "quantum" used to describe an interconnect or a fuse.

Your other responses are helpful but raise other questions in my mind that I will hold in reserve for now. Thanks for your patience.

I have been complaining about that on this forum over and over again.  Only be direct questioning can one find out what the input impedance of these "current driven" phono stages actually is, and it's typically from a few ohms in the best case to as high as 20 ohms. 

@lewm I don't know how you could specify the input impedance; it varies with the impedance of the cartridge! Again, the gain of the circuit is defined by the ratio of the feedback resistor vs the input resistor (which is literally the cartridge itself). So if the cartridge is 30 Ohms and the feedback resistor is 300 Ohms, the gain of the circuit would be 10 or 10dB. If the cartridge were only 15 Ohms that would mean the gain of the circuit is 20 (16dB). So the input impedance can only be defined by the fact that a virtual ground is present. But you have another problem, which is that with almost any opamp made you run out of Gain Bandwidth Product over about 20dB of gain or thereabouts.

This means that with cartridges that have a very low impedance the circuit may lose neutrality. Personally I would prefer to have the gain be a set thing so that the cartridge would not be able to affect the phono section in that manner.

I haven't kept track of which current driven phono stages on the market use op amps or discrete transistors or tubes in the input I/V stage, although I don't know of any that use a tube or how you could use a tube in that fashion.  However, I would guess that many do use a discrete transistor and so by your definition cannot be current amplifiers.  If they all use op amps, then I stand corrected, and right there I have learned something about them.  However, every one that I have investigated was said to have some finite input Z, greater than zero and notwithstanding the cartridge with which it might be matched. (Especially because most of the advertising suggests you can match them with any cartridge having a "low" internal resistance, low being better than higher.)  But I do get that to be a pure current amplifier, the input impedance ought to be zero. Sticking my neck out in saying this, but I would rather gain understanding than worry about negative feedback, no pun intended.

OK... lets try a different tact since i do not think ground (be it virtual or real) matters in this situation.  I am simply relying on Ohm and Kirchoff for this ideal case.

Take a 30Ω cartridge and hook it up to an ideal voltage amp and then another one and hook it up to an ideal current amp.  Now take two AC microamp clamps and monitor the current output of each cartridge.  Will the currents be the same for each cartridge?

dave

Ralph, I just had a “duh” moment. Sutherland describes the input of his Loco and Little Loco as a “virtual” short circuit. I had heretofore interpreted that word in its more literary sense; virtual meaning “nearly “or “close to”. Thanks to your input, I now see he means it electronically (virtual). I also see that nearly all current drive phono stages do use an op amp input. The BMC MCCI being an exception. It connects the cartridge output to an the emitters of array of discrete transistors.

Too late to edit my post, but I meant to say, "It connects the cartridge to the emitters of an array of discrete transistors."  Not "It connects the cartridge output to an the emitters of array of discrete transistors."

Sounds like driving a triode via its cathode, but I won't dare go there.

I haven't kept track of which current driven phono stages on the market use op amps or discrete transistors or tubes in the input I/V stage, although I don't know of any that use a tube or how you could use a tube in that fashion. 

@lewm Transimpedance preamps have to use opamps since that is the only way to get a virtual ground. You can use discreet opamps as those do exist (a friend of mine designed his own) but you do need an opamp to pull it off.

Take a 30Ω cartridge and hook it up to an ideal voltage amp and then another one and hook it up to an ideal current amp.  Now take two AC microamp clamps and monitor the current output of each cartridge.  Will the currents be the same for each cartridge?

@intactaudio I doubt it but that depends on the actual impedance that the cartridge is driving in either case.

Take a 30Ω cartridge and hook it up to an ideal voltage amp and then another one and hook it up to an ideal current amp.  Now take two AC microamp clamps and monitor the current output of each cartridge.  Will the currents be the same for each cartridge?

@intactaudio I doubt it but that depends on the actual impedance that the cartridge is driving in either case.

@atmasphere @intactaudio 

I think it depends on the individual design.

I know from first hand knowledge that the BMC & ESE Nibiru react differently with different cartridges, but on the other hand I have a bespoke current sensing device built by a cartridge manufacturer that is superb across all my cartridges ranging from 3-40ohms internal impedance.

Also I recall the current sensing Goldmund PH2 sounding superb across a variety of cartridges, regardless of internal impedance of the MC.

@dover  This needs to be distilled to the most basic level to get a solid foundation that everyone can build upon equally.  It is not about any particular design and more about cartridge loading as a whole.  My belief is that the nature of current amplification vs. voltage amplification (namely how they load a cartridge with low vs high impedance) has a dramatic effect on the mechanical behavior of the cartridge and may be partially responsible for the differences heard between the two types.

I am not suggesting that all current amps are the same but if we can separate them conceptually from their voltage amp brethren then a discussion about how each loads a cartridge can ensue.  

 

dave

My belief is that the nature of current amplification vs. voltage amplification (namely how they load a cartridge with low vs high impedance) has a dramatic effect on the mechanical behavior of the cartridge and may be partially responsible for the differences heard between the two types.

 It also has a lot to do with distortion and RIAA EQ differences. Separating those out might be a bit difficult.

Ralph, in an ideal current driven phono stage that uses an op amp to sense current, is the coil of the cartridge connected to that virtual ground that you describe? One end of course. If that is the case, where do they connect the other end of the coil? Thanks.

if I am understanding both Ralph and Dave correctly, there is a difference between them in the definition of a current driven phono stage, in that Ralph says it must be an op amp that does the current to voltage conversion, and which can provide a zero ohm virtual ground. Whereas, Dave said that any device with an input impedance much lower than that of the cartridge internal resistance can act as a current driven stage. Is that correct?

Whereas, Dave said that any device with an input impedance much lower than that of the cartridge internal resistance can act as a current driven stage. Is that correct?

I am not suggesting that if the load is a fraction of the cartridge impedance the stage must be a current amplifier.... I am suggest  as a whole current amplification stages will typically load a cartridge with less than its internal impedance.  

A good example of this is the situation I outlined above where I used an 8Ω cartridge through a 1:8 SUT and then directly compared it to a 1:40 with a 2.2Ω resistor across the cartridge directly.  The 2.2Ω resistor was chosen so that the output of the SUT in both cases was identical as was the frequency response from 10Hz to 100kHz.  (±1dB).  In this case even though the cartridge load was 1/4 the internal impedance when using the 1:40,  I would still consider it a voltage gain stage. 

The result of this experiment was interesting.  Even thought the gains of both situations were the same, the 4.7kΩ load through the 1:8 sounded a good 2dB louder.  When the gain of the 2.2Ω load was bumped 2dB suddenly it was preferred and then going back to the 4.7kΩ 1:8 at the same +2dB level started to hurt my ears. 

dave 

in an ideal current driven phono stage that uses an op amp to sense current, is the coil of the cartridge connected to that virtual ground that you describe? One end of course. If that is the case, where do they connect the other end of the coil?

@lewm 

Ground.

The result of this experiment was interesting.  Even thought the gains of both situations were the same, the 4.7kΩ load through the 1:8 sounded a good 2dB louder.  When the gain of the 2.2Ω load was bumped 2dB suddenly it was preferred and then going back to the 4.7kΩ 1:8 at the same +2dB level started to hurt my ears. 

@intactaudio 

Transformers transform impedance. Further, to prevent ringing they must be properly loaded at their output, to something called 'critical damping' where a squarewave input to the transformer results in minimal overshoot.

If not loaded the transformer can 'ring' with excess harmonics- its making distortion. Your ears will respond to that as sensing it as loudness and yes, it might even hurt if the volume is up a bit.

Because transformers transform impedance its not necessary to load the cartridge directly with a low impedance in order to achieve a low impedance- you can do that on the output side of the transformer as well. IOW putting a lower impedance load on the output will reduce the load impedance the cartridge sees. This is because the only isolation a transformer offers is galvanic and DC; it does not offer impedance isolation. 

This loading issue is one reason I avoid SUTs- you do have to manage their care and feeding. If the SUT is designed for a specific cartridge, the correct load is probably 47K (but will be different if a different cartridge is used). Its really important to keep interconnect cable capacitance to a minimum. But if you simply have enough gain and your phono section has no worries with the RFI that will be generated by the cartridge/cable interaction, then you have no worries- its plug and play. 

I have been following this thread with great interest, and have been learning a significant amount!

Is there any chance the major contributors to this thread will be designing, producing, and selling a new type of phono stage in the near future?  

I certainly hope so!

Is there any chance the major contributors to this thread will be designing, producing, and selling a new type of phono stage in the near future?  

We've been making phono sections since 1989. Our MP-1 had the first fully differential balanced phono section made.

Atmasphere......The Ah-Ha moment!

http://www.atma-sphere.com/en/mp-1.html

Is this the company you represent? 

I apologize that I did not recognize you as a tier one supplier of high quality phono stages.  I will study your web page further.  

Thanks for being involved with Audiogon and sharing your knowledge!!

Lou

If not loaded the transformer can 'ring' with excess harmonics- its making distortion. Your ears will respond to that as sensing it as loudness and yes, it might even hurt if the volume is up a bit.

That is not the case in this instance.  The measured frequency response of both cases is within 0.1dB within the audio band and the 1:40 has a 2dB low Q resonance at 90kHZ and the 1:8 has a 6dB peak @ 235kHz.  To isolate the contribution of the SUT I left the 1:40 unloaded to reflect 187Ω and placed a 200Ω resistor across the primary of the 1:8.  I then level matched them and am hard pressed to tell the difference between the two.  This gives me confidence in my belief that the load on the cartridge is responsible for the sonic changes that I reported above.

dave

 

That is not the case in this instance. 

This gives me confidence in my belief that the load on the cartridge is responsible for the sonic changes that I reported above.

I don't doubt that it could be affected. Loading the cartridge causes the cantilever to become stiffer (more work is being asked of it and that has to come from somewhere: the cantilever is thus harder to move)- and thus can introduce the possibility that even though the bandwidth of coil is unaffected, the mechanical aspect of the cartridge will be affected by that added stiffness- possibly making it less able to respond to higher frequencies.

The distinction between virtual and actual ground is a subtle one.

When an opamp inverting input is used, the virtual ground is extremely similar to a real ground as the action of negative feedback makes it so. The difference is in the error term- i.e. the output voltage divided by the open loop gain of the amplifier, together with any impairments added by the amplification system.

This difference can be extraordinarily small, so arguing that the virtual ground is not a real ground is largely facile. 

As far as the source is concerned there can be essentially negligible difference between a real ground and a virtual ground.

Claiming, arbitrarily, that it is prima facie audibly different as far as the source is concerned is not reasonable. 

To put this in context. The error term is a function of the opamp gain bandwidth product, open loop DC gain, and the internal sources of distortion,  both the intrinsic input non linearity and the output stage non linearity. With high gain bandwidth and high open loop DC gain the error voltage is extremely small in the audio band, and with low intrinsic open loop distortion at the signal levels present at the non inverting input when negative feedback is applied the resultant distortion component of the error signal is also extremely small.

These facts make the virtual ground , when opamps of sufficient quality are employed, extremely close to an ideal ground, in fact just about as close to an ideal ground as any "real" ground that you can actually construct.

A copy of a post I placed a short time ago...

 

I'm in the process of having a phono preamp made manufacturable by a well known audio company. The first thing they insisted upon was that the design would be implemented in SMD- purely for manufacturing purposes. This had it's own unique set of difficulties- for example, some of my preferred capacitors were not available on SMD, so a search for suitable items of a different technology (ceramic MLCC C0G vs Polypropylene film) was needed, together with a proof that the distortion characteristics were essentially equivalent.

The other aspect was that the preamp design investigated two possible implementations, either a voltage mode input, or a current mode input, and with the 75uS RIAA TC implemented in the first stage.

I ended up with a voltage mode input, as when designed for equivalent gain and RIAA characteristic there is, generally, no measurable or audible difference.

However, there are indeed differences in operation and implementation.

To put this somewhat in context, I designed a number of "transimpedance" amps while at ADI, most notably the AD846, together with a number of conventional opamps, so I am familiar with the concepts. The AD846 was designed to have almost perfect current conveyance properties and could be operated open loop as a transimpedance amplifier. Most opamps/amplifiers use negative feedback to achieve this goal, or have high distortion levels if operated open loop.

As I don't want to make this into a "white paper" I'll try to be brief.

1. A phono cartridge is a voltage generator (Vs) with an output impedance which is mostly a resistance in series with an inductance (R+Ls). This can be converted into the Thevenin equivalent current source- which is a scaled current (Vs/(R+Ls)) with the output impedance in parallel to ground.

If you take this current and drive it into a virtual ground, which shorts out the shunt components, and convey it to the load resistance (Rl) then the output voltage is Vs*Rl/(R+Ls). If Ls is small then the gain is completely dependent on the series resistance of the cartridge and will vary from cartridge to cartridge, and if LS is large there will be a HF roll off.

Any shunt capacitance will be essentially ignored.

If there is a resistor added in series with the virtual ground, then the current is shared between the equivalent shunt components and the series R, and the gain becomes even more variable.

Voltage mode lacks this complexity. Provided the load impedance is relatively large compared to R the gain is easy to determine.

However, the shunt capacitance is not ignored, but for MC cartridges the inductor is so small that all parasitic capacitance values are irrelevant, assuming the load R is small enough to damp out the LC resonance. 

Current mode does not experience this resonance, but correct loading Rs plus a phono stage with a suitably good ultrasonic overload margin will take care of the potential problem.

MM cartridges into a virtual ground are not rational unless there is a very large resistor in series with the virtual ground. This is because the R is large but L is even larger.

 

2. In voltage mode the input stage is non-inverting and will experience potentially substantial deviations about ground. For many opamps, particularly earlier generations than the most recent ones, this voltage will cause increases in distortion due to the operating conditions of the input transistors being changed. 

This distortion can be highly sensitive to the source impedance and the input signal level.

In the transresistance mode the virtual ground does not move, removing this source of distortion.

Modern audio IC opamps are generally designed with this problem in mind and exhibit negligible changes in distortion when operated in non-inverting mode.

These are the two main aspects of current versus voltage mode inputs.

There are other, more obscure, aspects.

I chose voltage mode, but also chose appropriate opamps to minimize the down side of the choice.

The bottom line is, when properly designed both current and voltage input designs can have equivalent performance from the perspective of distortion, frequency response etc.- but the voltage input design is more predictable and easier to specify. 

The voltage input design produced has very precise gain, extremely precise RIAA compliance and unmeasurably low distortion.

 

 Report this

Dear @mijostyn  : After reading the Wyn posts are you still thinking of the current phono stage superiority over the voltage designs PS you supported?

 

R.

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.

Dear @mijostyn  " did order an ultra accurate RIAA board but I am already set up to do digital RIAA correction. "

If you have that ultra accurated inverse eq. RIAA why do you think you could need digital corrections to that accurated analog RIAA?

 

Maybe you know   " something " that I don't " see " down there.

 

R....

Well, maybe because in the analog media the signal pass through more passive parts than in the digital domain? . Even in today LPs you know if that LP was recorded in the digital domain and you will know for sure listening the bass range that's a main advantage of digital over analog.

 

R,

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

If we accept this to be the case (and I do) then the next logical step is to agree that we are simply discussing varying degrees of mistracking.  Treating mistracking as black or white serves little purpose in this discussion.

Wyn proved that loading does not affects the tracking cartridge abilities

Where is this proof?

you will find that the parameter that needs to be changed is the compliance

In your stack of 20 test records I assume you also have CBS STR-100 which has a test for compliance.  

It is interesting to note that the telltale here is also mistracking.  Again to repeat myself... If you accept that according to Lenz that loading a cartridge will stiffen the cantilever, how can that not effect the compliance?

dave

 

Dear @intactaudio : This is what I posted and pasted from what he posted and came from a years ago cartridge loading thread. The loading/tracking is not a new issue but an " old " issue discussed here and in other internet audio forums:

 

 

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. """

Btw, yes I have too that test LP and is logical that when we are mesuring/talking of compliance tracking always comes in the analysis.

Cartridge compliance is so important that can " change " what we are accustom to do on the tonearm/cartridge resonance frequency issue that tell us that that resonance frequency must be in the 8hz-12hz ( around it. ) frequency range and the compliance has the " power " to does this:

the LOMC Ortofon MC2000 model was reviewed in the 60?s by the Audio magazine, the cartridge was mounted in a Technics EPA 250 that was mounted in the Technics SP-10MK2.

Well the cartridge weigth is 11grs. and the measured compliance was over30+ cu and along that tonearm its resonance frequency was as low as 5hz. Go figure ! and guess what : that tonearm/combination that in theory can’t run together had no single tracking issue with the true test Telarc 1812. Why that kind of success? because that really high compliance that gives that cartridge those extraordinary tracking abilities and I owned not one but 3 samples of that cartridge and you can be sure that at any loading will has not tracking issues.

It’s impossible that loading can change the compliance in a LOMC cartridge in a cu levels that provoque added mistracking to the usual cartridge levels, no way.

I’m not against that loading stiff the cantilever the real subject is that that stifness micro micro microscopic level that exist can´t be of the necessary magnitud to cause adding mistracking.

As @mijostyn posted: silly to think in other way. Now, in the other side no one including the person that supports that till today never proved that added mistracking by changes in cartridge loading.

I understand you but I think is useless and futile continue talking of something with out true prove. Don’t you think?

 

On other topic and thank’s to your last post that shows that Benjamin B. Bauer was the CBS laboratory Vice-president I learned that that Mr. Bauer is the same gentleman that in 1945 along names as Baerwald, Stevenson, Pisha and obviously Löfgren developed too  equations/solution for tonearm/cartridge alignment: exist a Bauer alignment

R.

Cutting and pasting text without any reference to context is not proof.

Where was it ever proposed that heavy loading causes additional mistracking?  It has been my contention that exactly the opposite may be occurring. Everything you mention specifically refers to it being impossible for heavy loading to cause mistracking with which I concur.  However the possibility that heavy loading may actually reduce mistracking hasn't been mentioned or covered by anyone beyond Moncrief that I know of.

dave

@intactaudio , I think miss-tracking distortion and IM distortion are two separate but additive issues. 

There is a big difference between normal cartridge loading and an impedance approaching zero. This is all conjecture (theory?) at best. I have not seen a study done on tracking ability vs cartridge loading. I have seen distortion measurements on the same cartridge run voltage mode vs current mode and distortion is certainly lower in current mode. I think this is me agreeing with @rauliruegas again. It is indeed a strange world. 

@rauliruegas , I will run the Seta in both modes with and without digital RIAA correction to see if I can tell a difference but it will be a while. Rob has told me my phono stage is 4 to 5 weeks away. I still have not cornered a cartridge yet. All the cartridges I am interested in are "special order" and it seems nobody is making anything at the moment.  

Mijo,

I agree that there is a big difference between loading @ 47kΩ and loading approaching zero.  These two extremes very closely represent the "ideals" of current vs. voltage amplification.  It may very well be conjecture but discussion of this on the most basic level is the only way to get a common solid foundation for everyone to build upon.

 I have seen distortion measurements on the same cartridge run voltage mode vs current mode and distortion is certainly lower in current mode.

Interesting.  Now the question becomes what was the cause of the distortion change?  I see two possible options:

  1:  The distortion of the two modes of operation were different.

  2: The effect of the radically different loads altered the behavior of the cartridge resulting in different measured distortions.  

Chances are the difference is some combination of the above two and simply removing the cartridge from the tests and using a sound generator should illuminate the differences between the two modes of operation. Repeating the measurements with a number of different cartridges should also illuminate if there is a specific pattern happening.  

 

dave

Dear @intactaudio  " the possibility that heavy loading may actually reduce mistracking hasn't been mentioned or covered by anyone .."

 

I did it.Over the years participated in no less that 8 threads about cartridge loading here and wbf and in one of them I posted something as:

 

stifness of cantilever it's a good thing because cartridge designers normally looks for the stiffer cantilever material as Boron, higher stifness the better in favor of better quality level listening performance.

Anyway, all is done.

 

R.

Dear @mijostyn  : Thank's. The we will see.

 

R.

Ok guys, I'm getting dizzy.

@rauliruegas , I already have that test record!

Channel D has received my wire transfer ($500 credit) and A friend says the Platinum Signatures will arrive any day. I might also get an Ortofon Verisimo., teeter tottering on that one. Since I can run the phono stage 4 different ways and I can record records to the computer I will be able to make 192/24 files of all the results which I can download so everyone can judge for themselves as long as your system can play files. If not then GET WITH IT. Digital is hear to stay (spelling intended). It allows you to do cool things you can not do otherwise and share the results with friends. 

@rauliruegas  I have no idea what is better but I will figure it out and I will be happy to email you the files so you can compare. Then you can tell me!

@mijostyn  : " Digital is hear to stay .."

With out single dude. Good.

R.

 

 

For the record (if you see what I did there) I've never stated that loading a cartridge would cause mistracking! That is simply Raul with his usual logical fallacies again (in this case, the classic Strawman).

What I have stated is that loading the cartridge will cause the cantilever to become stiffer. This fact is unavoidable as anyone grounded in generator and alternator theory knows. This does not mean that the cartridge will mistrack. It means what I said: the cantilever will be stiffer; whether that affects the performance of the cartridge is another matter and other than suggesting that it might affect high frequency tracing ability. I've also been careful to not state what frequency, which may well be ultrasonic; at any rate obviously is an unknown.

Raul, in his on-going quest to simply make me wrong, has been trying to put words in my mouth. Fortunately I'm way to far away for him to actually do that 😁

@atmasphere 

I gave up when Raul confused cantilever material with cantilever motion ( see quote from Raul below ).

The reality is that any change of loading will possibly have an impact on "tracing the groove". The Shure white papers explain this clearly with their testing on groove tracing and the impact of changes in compliance - at worst they describe scrubbing motion of the stylus/cantilever from mismatched arms/cartridges. It is the genesis of the use of their stabiliser brush. Tracking tests on records do not measure distortion - they only indicate a tracking ability ( crudely ).

In my view there may be no obvious mistracking from altering the loading, but there is the possibility of a change in tracing and distortion ( for better or worse ). 

If Raul loads all MC at 100ohms, then likely he cannot hear the impact of changes in loading, or he has a low resolution system - or both.

As an aside I agree with JCarr's and your comments that loading is more about taming poor quality phono stages with poor overload margins at ultra high frequencies. Folk need to understand that, like brick wall filters in early digital, problems at ultrasonic frequencies can generate artefacts down into the audible region. Perhaps Rauls home brew preamp is in this group which would explain why he needs to load all MC's at 100ohms - which is extremely low - particularly for cartridges with an internal impedance above 5-6 ohms. It's no wonder that Raul thought for years that he preferred MM cartridges most of which have large phase shifts and frequency aberrations in the audible region - necessarily tuned by loading R & C of course in order to get a reasonable facsimile of a linear phase coherent response. 

 

I did it.Over the years participated in no less that 8 threads about cartridge loading here and wbf and in one of them I posted something as:

stifness of cantilever it's a good thing because cartridge designers normally looks for the stiffer cantilever material as Boron, higher stifness the better in favor of better quality level listening performance.

The distinction between virtual and actual ground is a subtle one.

When an opamp inverting input is used, the virtual ground is extremely similar to a real ground as the action of negative feedback makes it so. The difference is in the error term- i.e. the output voltage divided by the open loop gain of the amplifier, together with any impairments added by the amplification system.

This difference can be extraordinarily small, so arguing that the virtual ground is not a real ground is largely facile. 

As far as the source is concerned there can be essentially negligible difference between a real ground and a virtual ground.

Claiming, arbitrarily, that it is prima facie audibly different as far as the source is concerned is not reasonable. 

@wynpalmer4 The virtual ground is one thing when it is driven by a resistance in series with the input (which might be a cartridge). Its a bit different when the cartridge itself is that resistance. WRT actual ground, I think we can both agree that a cartridge driving a dead short will not produce anything that can be amplified. A virtual ground is different in that manner 😉

One thing that has come up in this thread is the mention of Lenz's Law, which has to do with the radiation of a magnetic field from a conductor when conducting. Its been brought up in the context of 'back EMF'. I've not been able to discern how this is supposed to work; if driving a loudspeaker (which has significant inductance interacting with a magnetic field) you do get back EMF but in the case of the cartridge an impedance (for the most part) very little inductance in the load is present. So I would appreciate an explanation; as best I can make out the back EMF would be insignificant WRT the source. 

Dear @dover : As always I respect a lot your opinions but what you are talking about me and my " audio life " trend certainly is far away to be reality.

If that’s really what you think then you are wtrong about and let me explain you:

 

no I don’t confuse cantgilever material with cantilever motion, I’m with @intactaudio on that issue , if cantilever goes stiffer that’s is a good thing but if the cartridge suspension goes stiffer then that is way different and in no thread/posts no one named " cartridge suspension ".

Wyn and PM proved that changes on loading develops IMD, as J.Carr posted too, but don’t cause mistracking and I agree ( not today ) but from several years now with.

 

@imhififan gaves me the advise to make loading changes tests and he and I did it. I did it with different cartridges and one of that cartridge was the Denon 103 that by coincidence was the one he choosed too and both of us with different room/system experienced no mistraking issues by loading changes.

 

 

 

I know perfectly the impact that loading has mainly in the phono stages and in way minor way the impact in LOMC cartridges.

You are wrong about my phonolinepreamp that is designed with a really high headroom and is totally inmune of those poor designed phono stages even that my preamp frequency goes over 1.5Mhz.

@lewm owns the same unit, please ask him. No I don’t need per sé to load at 100 ohms when almost all LOMC performs the better with that load, theory of loading cartridges is theor and we know that some times what theory says does not happens under play.

 

Wrong too that I prefer MM cartridges, it’s not that way. Several years ago and due that I owned some MM/MI cartridges that were in closet I decided to give a listen to it and then I discovered to me that with today room/systems MM/MI cartridges can play with high quality performance levels and from there came that very long thread on MM cartridges.

In the other side ( maybe you born in audio with a LOMC cartridge in your hand. ) my very first cartridges in audio were all MM/MI that were the ones I re-discovered several years later and my first LOMC cartridge was the same Denon 103 that I used on the loading tests. In those times I owned Pioneer top of the line electronics and its HPM 900 speakers.

 

Btw, I posted several times that I’m not against the theory of that stiffer issue and I don’t want to add more comments about when all is done by the gentlemans that really has the knowledge high levels and first hand tests about even one of them made several tests in other thread in the same loading subject in real time because he has the modeling tools for it: yes that gentleman is Wyn. Can you do the same with the same knowledge levels?

No one is perfect and certainly you and me are far away from there.

 

Btw, please don't follow try to hit me because you can't and I'm not like you and I'm not to start speaking of each of your system audio items you own, so stay calm and cool.

 

R.

Figure from the Wiki page on Lenz Law. I was driven to read about it after Dave mentioned it.

 

The virtual ground doesn't care what the origin is of the impedance in series with the voltage source. An ideal virtual ground simply means that all of the current that enters a node is conveyed somewhere else with a zero change in the voltage at that node.

An ideal opamp with infinite gain and bandwidth will be a perfect virtual ground, just as a perfect ground will have zero impedance to "real ground".

From Wikipedia.

"Lenz's law, named after the physicist Emil Lenz (pronounced /ˈlɛnts/) who formulated it in 1834,^[1] says that the direction of the electric current induced in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes changes in the initial magnetic field.

It is a qualitative law that specifies the direction of induced current, but states nothing about its magnitude. Lenz's law predicts the direction of many effects in electromagnetism, such as the direction of voltage induced in an inductor or wire loop by a changing current, or the drag force of eddy currents exerted on moving objects in a magnetic field."

To paraphrase, a changing magnetic field is created that opposes the changing magnetic field that creates it.  That in turn will create a "restoring force" to oppose the motion that created it in the case of a cartridge.

Lenz's law says nothing about the magnitude of that field and hence that force.

That's a much more complicated exercise as there is no simple, closed form, equation for it. It can be estimated/approximated very roughly assuming some level of reciprocity, but I have no intention of going into the arcana of this.

The point is that IT IS small compared to the mechanical forces being applied to the cartridge due to the reaction of the walls, and that it does increase as a function of increasing frequency.

Incidentally, I don't intend to further participate in this exchange.