Cartridge loading

When you say, RFI, are you talking radio frequency interference, or in general, electro-magnetic interference (EMI)?

@antinn Thanks for your comments!

RFI, not EMI. The RFI is caused by the tank circuit created by the cartridge inductance and tone arm cable capacitance. It is driven into excitation by the cartridge energy.

Don’t really buy the RFI argumentation, sorry. Putting aside simple and super cheap solutions like grid stoppers existing for decades, I cannot see how the RFI conspires to always give the effects exactly mimicking underloaded (high R) cartridge.

@bydlo

Grid stoppers amazingly are not used in all phono preamps! Some designers have ’not heard the gospel’ so to speak ;( But more to your point, I’ve yet to see an audio circuit that sounds right if it is having problems with RFI. The ’cartridge loading resistor’ detunes the tank circuit at the input of the preamp. With most preamps if they are RFI sensitive, this will cause them to be less bright as there will be less intermodulation. Intermodulation contributes to brightness as the ear converts all forms of distortion into tonality.

the cart model of Shure brothers analyzed there is *unloaded* (plus the current source is strangely drawn with series (??) instead of parallel source impedance). The R on the schematics is the mechanical damping of the suspension, not the loading R.

Shure to my knowledge never made a LOMC cartridge. My comments about RFI relate only to low output cartridges. MM cartridges are an entirely different matter, as the resonant peak is often at or near the top of the audio band. They are also capable of ringing at audio frequencies as their inductance is so much higher, so to use a MM effectively, proper loading **is** required.

@intactaudio That is what the 47K input standard is supposed to be for- a slight amount of damping. I don't see in the text you quoted how the cartridge was set up- was it driving a very high impedance as a control or 47K?
@antinn  The interesting article you linked refers to self-resonance of inductors as a consequence of using them in equalization circuits. I don't see anything in that article about how the RFI generated by a cartridge can interact with the phono section. Pete Millet's website is quite an asset to those interested in audio!


What I have found is that there are two aspects of RFI issues in phono preamps. The first is pretty obvious; the resonance of the tank circuit caused by the cartridge inductance and the tone arm cable capacitance. This can cause overload of the input circuit if it has poor overload margins. The other is less obvious which is the inherent stability of the circuit. There is a device known as a 'stopping resistor' which is used to prevent oscillation at the input of a grid (in the case of tubes) or gate (in the case of FETs). But some designs don't use stopping resistors and can oscillate briefly if presented with the right circumstances. This is how a phono section can generate ticks and pops; this is a fairly common problem is why many people think than LPs are a lot noisier format than they really are. 

atmasphere I'm not questioning if you have a conversation with JC.

Good. Because you misread an earlier comment of mine and came up with this nonsense:

Atmasphere mentioned WBF where JC participated and in that forum JC never mentioned that " limit trace... " that ( for me ) exist only in the atmasphere imagination

What I had said was not that Jonathon had written about it, I said that he and I had a conversation about this issue at Munich. Very specifically it was he that brought up the compliance of the cantilever being affected by the load the cartridge has to drive IOW becomes stiffer as the load resistance is reduced. Anyone familiar with electronics would instantly see how this is the case.

Now, if someone can find International Audio Review 5, 1980 pp.31-159, the answer to the existental challenge of prove-it may be answered.

A simple understanding of how electro-mechanical transducers like loudspeakers and cartridges work is all that is needed. It should be no surprise that Moncrieff experienced something like this; what is surprising is that it was not reported earlier, but its been my position for the last 20 years or so that the implications of using a transducer based on an inductive principle haven't been fully realized by the hifi industry.


It was pretty obvious to me all that time ago that most phono section preamp designers were not taking into account how the resonance created by the cartridge inductance and the capacitance of the tone arm cable interacts with the phono preamp. Its not just a matter of enough gain and proper EQ; its also a matter of RFI immunity and internal stability of the circuit. If the latter two are properly addressed the need for cartridge loading for a LOMC cartridge is moot.

 As for 47K being the optimal load, I see all kinds of manufacturers suggesting values other than 47K as the optimal load for their cartridges.  

47K is the industry standard; as far as what it the optimal load that is what this thread is about :)

47K only work under a limited range of circumstances - mostly whether or not the phono section is stable enough to deal with the ensuing RFI to which it will be presented when dealing with that impedance. A secondary issue is whether or not the cartridge was built with some form of electrical damping in mind with the intent of thus creating mechanical damping. This seems problematic as the compliance of the cartridge is directly affected- that being the case a range of loading values would be specified for a given effective mass and we certainly are not seeing that in the spec sheets!

I wouldn't worry about whether a cartridge is a voltage or current generator- the simple fact is current does not exist without voltage and vice versa. I think this might have come up on account of current amplifier phono sections, which have that low 'virtual ground' thing going on.


Just because its a current amp does not mean you need the source to make only current.

At any rate, a cartridge makes **power** since its a generator; there is voltage and current at the same time.

My personal take on it is that the coil generates what you tell it to. Leave it open it generates voltage, Load it down it generates current.

@intactaudio 

To be clear, a current amplifier does not significantly load the cartridge. The 'zero ohms' thing that you see talked about in reference to them refers to the virtual ground with which the cartridge plays a part. Virtual ground being nearly zero ohms is **in no way** similar to actual ground!! So the cartridge does not behave as it its driving a short. It behaves as if it is driving a fairly high impedance. This may sound counterintuitive, but a virtual ground is a thing that has to do with how OpAmps work and if it was really the same thing as zero ohms, the OpAmp wouldn't work. Another way of putting this is that 'virtual ground' is a charged term in that it does not mean 'ground' at all. The word 'virtual' means something different than 'actual' :)

when you say "ability to trace" are you referring to the output generated by the cartridge or the physical ability for the stylus to remain in contact with the groove wall?

I am referring to the simple fact that a stiffer cantilever will be unable to trace higher frequencies- at some point, it won't be able to follow the groove wall impressed with higher frequencies. This point may be outside of the audio band, but the way some people try to use loading resistors as a tone control, with some cartridges I suspect it will be inside the audio band too. Regardless, by loading the cartridge in a significant manner, causing the cantilever to be less supple is unavoidable.


The reason I do not think cartridge designers design for any load other than 47K is twofold: first, 47K is the industry input impedance standard for phono preamps. Second, I had a conversation with Jonathan Carr (well known of Lyra fame) on this very topic and it was he who mentioned to me that loading at 100 ohms or the like would have the effect of reducing high frequency performance (this conversation occurred in my room at the 2014 Munich show; we had both been active on a thread on cartridge loading that can be found on the 'What's Best' audio forum). This issue was at the heart of the conversation- it was not about anything else. Now as a phono preamp designer, having this conversation with a top cartridge designer, and understanding basic physics of how transducers work, this confirmed my own work in the area. He and I are on the same page with anything to do with cartridge loading, not just the cantilever stiffness issue.

If you know how electro-mechanical transducers work, you can't come to any other conclusion. To make things easier to work with, we humans often simplify a picture so we can deal with basic concepts. Making the cartridge output invariant as if it somehow does not obey Ohm's Law and basic generator theory (see https://en.wikipedia.org/wiki/Generator_(circuit_theory)) is one of those ways of simplifying a concept.  But if you understand that a cartridge is a generator, maybe this idea is easier to understand in that a conventional generator which is spun to make electricity, the generator shaft becomes progressively harder to spin the more the generator is loaded. A cartridge **has** to have a similar behavior!

So, your " limit trace ..." statement continue be false.

Your feculent argument is also specious. You can't have it both ways.

"" electrical damping of an electro-mechanical transducer results in less high frequency output of that transducer. ""

no one is questioning that ( at least not now. and is not what I asked several times here and in other threads. ).

So we are in agreement as seen above. That is the same as:

What I asked you are true evidence of your statement about that:

""" LIMIT TRACE....."""

IOW when the cartridge is loaded (damped) its ability to trace high frequencies is reduced because the cantilever will be stiffer. If you agree with your first post above as you say you do, then you have to agree with this also. They are the same.

Your post is not an answer to what I asked to you:

Simply put, I've answered your question directly several times in this thread alone. I've been avoiding saying this, but at this point its apparent that you don't understand the answer;  you respond with literally:

Bla, bla, bla, bla, bla, 

Again, electrical damping of an electro-mechanical transducer results in less high frequency output of that transducer. I suggest you study the topic with the same sort of energy that you've used in your attacks.

Let me know what you think now when that guy cracked it and explained why the input impedance is almost ZERO

@chakster This statement isn't correct. The **virtual ground** is almost zero, not the actual input impedance. Its a bit tricky explaining what the difference is but put it this way, if you turn the unit off you'll find that the actual input impedance is quite high. Apparently it has a pretty good opamp, since that is required in order for the virtual ground to approach zero.

What I experienced always is that at 100 ohms quality level cartridge performance is always better

If your phono section has RFI sensitivity what you state above will be the case as I’ve maintained also on these threads.


With regards to the load impedance affecting the cartridge, of course this happens. Moving coil cartridges work on the same principle as a loudspeaker; now think about a kid’s walkie-talkie that has the speaker also double as a microphone. In other words, the speaker can be driven by energy or it can make energy, because it is a **transducer**, and with any transducer motion is converted to electrical energy and vice-versa.


You can test this easily enough- remove the grill from your speaker and see how easy it is to move the woofer if nothing is attached to the speaker terminals. Then short out the speaker terminals and see how easy the woofer is to move then! With a cartridge its no different- the more you load it down (lower resistance loading resistor) the more work it will have to do and so the cantilever will be harder to move. Since this is also the idea of ’damping’ we can easily infer that mechanical damping of the cartridge will occur if the load impedance is reduced.


Anyone schooled in the electrical arts will understand this immediately; and thus also that high frequency output of the cartridge will be reduced as the cantilever is made to do more work. If this is not readily apparently please do more study of electrical theory.


Now there is one exception with regards to the input impedance of the phono circuit- the load impedance must be connected to the cartridge in such a way that it causes it to do more *work*. If the cartridge is not doing any work then it will be unaffected. Now refer to the article at this link previously given:
http://phonoclone.com/diy-pho4.html

We can see that the cartridge is actually being loaded by the input of the opamp; which if measured will be found to be quite high (most modern opamps are FET input). The idea is to replace the input resistor with the cartridge itself- so that the virtual ground (present in any opamp circuit) is the output of the cartridge itself. In this circuit the cartridge isn’t doing the sort of work as it would be if the cartridge were presented with an actual 0 ohms impedance!! IOW, zero ohms and *virtual ground* are not exactly the same thing! I refer you to OPAMP theory 101 as to why. As a hint, the closer the gain of the opamp is in open loop to infinity, the more the virtual ground will behave as it it is zero ohms **as far as the opamp is concerned**. This is more of a control theory thing which is far more text than I have time to put here, especially since you’ll need an EE degree to follow along. Just take it for now that a virtual ground isn’t the same thing as actual ground or zero ohms! If it were, no amplification could occur!

res ipsa loquitur

I’m not attacking him only asking for true proof/evidence of that " limit trace " that he spreads every where with out shows the evidence as foundation for.

The quote above belies this quote:

NO, I did not only ask for evidence and not more bla, bla like your bla, bla in your last post.

And both look antagonistic to anyone familiar with the English language.

I’m not attacking him only asking for true proof/evidence of that " limit trace " that he spreads every where with out shows the evidence as foundation for.

Just to be clear, yes, Raul, you attack me at every opportunity. This is well known by many others on this forum.


With regards to your need for proof- I recommend that you study the effects of damping on high frequencies. It is clear from your posts that at this time you have not done so.

please don't change the words. You posted several times:

  "" will limit the ability of the cartridge to trace higher frequencies .."""

I didn't. There is nothing above that suggests I did other than your text.

Where exist that evidence true evidence about because I don't see the foundations for your several years statements.

I see that you don't. But if I tell you that the sky is often blue, do I need to provide evidence, such as what 'blue' looks like? This is a similar problem; one based in engineering inherently understands that damping limits high frequencies.

no one never reported that a loading change or a 100 ohms load in a LOMC cartridge produce that tracking/trace HF problem ! !

To be clear, I have maintained and as we've seen on this thread, any damping will result in less HF response. Any LOMC cartridge these days has bandwidth far in excess of 20KHz; I can reproduce 35KHz sine waves I cut on my Westerex/Scully cutter and lathe system with a Grado Gold which is a MM cartridge which inherently has less bandwidth that LOMC. Since my cutter is bandwidth limited to 42KHz to prevent excess power from damaging it (this due to the pre-emphasis curve which boosts high frequencies at 6dB/octave) I've not been able to cut higher frequencies to see how high LOMC cartridges can really go, but I am certain that they can easily go past 60KHz.


I have not maintained as Raul claims that there will be a 'tracking/trace problem'; in fact I've been very careful about my use of English (not Raul's first language) to simply say that by causing the cartridge to drive a lower impedance it will of course be less able to trace higher frequencies. I've not said what those frequencies are. And I've also maintained that this is an area that warrants further study.


Raul has created a Strawman argument (and being a logical fallacy, therefore a false argument) that I've been saying that loading the cartridge leads to mistracking. I've not said that at any time; its my assumption that Raul's use of English not as his native language has led him in this manner.

The question is so what if at the end you can reach a natural balance? If you cannot, sth is wrong or substandard.

Yes.

I listened to all them with and with out the damping mechanism and differences are not small.

Damping mechanism?? If you are talking about the damping trough on the arm, you have missed the point of the conversation between @bydlo and myself entirely.

But what I meant is the mechanical damping of the stylus, not electrical damping of the LC tank.

Yes. If you pass a squarewave through an inductor, the more inductance there is the more it will ring; If you then place a resistance in parallel with the inductor this will cause it to ring less. When the resistance is the right value, the resulting output signal will be the closest you can get to a square wave. This resistance value is the 'critical damping' value for the inductor.

But LOMC cartridges really don't ring at audio frequencies. Now we can conclude from this that the damping of the coil is irrelevant except for the tank circuit, and the latter is of no importance unless the phono preamp has troubles with RFI at its input. But damping of the mechanism (cantilever and suspension) is a different matter, and its pretty safe to conclude that if it is damped, high frequencies will be attenuated. There are plenty of examples of this.


But I'm not sure how important this is. If the cartridge is properly set up in the arm and the arm is able to track the cartridge correctly, **and** if the phono preamp is unresponsive to RFI and is also inherently stable, then IME the stock 47K load has yielded the best results. I do think its an interesting topic though and think it bears more research.

You followed posting your opinion and some " answers " but as in the fast you just followed failen to prove the MAIN SUBJECT under debate that you stated in this thread:

""" will limit the ability of the cartridge to trace higher frequencies .."""

Actually I explained that in some depth. I recommend you go back and read my posts and those of intactaudio and bydlo again.

Electromagnetic damping due to a low R is actually quite an attractive (at least on paper) way of damping.

I agree, it is. But the inductance of a low output moving coil is so low that resistive damping has little effect, as in a nutshell the inductor does not ring at audio frequencies or anywhere near them.

I don't say that achieving critical damping is doable or even desirable from the sonic perspective.

I got that from @intactaudio 's comment about sidebands. I apologize as I did conflate your comments and his. Critical damping of the cantilever is one of the very few explanations I can think of for the phenom he described.

I think here lies the answer - "depending on the cartridge". I can imagine that for some cartridges, or better yet, some cartridge/tonearm combinations, the extra damping from a low R, combined with other factors may compromise the tracking. What I fail to see however is that this should be some universal law.

Its not so much a universal law as it is something to be aware of. If you have to use loading to achieve proper sound, it is a flag that something could be amiss: Instability in the phono section, a mismatch between arm and cartridge, that sort of thing.

lower R presents obviously more breaking force, opposing the stylus movement. This is the electromagnetic induction law in action: the current (flowing through R) creates the magnetic field that opposes the stylus movement. This force behaves like ~f/R.

This is what I've been maintaining all along.

Just to be precise, the energy is not presented in a form of a voltage because voltage alone cannot perform work. The energy is presented in a form of a heat, dissipated in the combined resistance of the circuit (R_load, the coil DCR, the cables etc), caused by the induced voltage applied to the resistance. This is ok. The question is so what? To speak of energy conservation, you have to look at all the forces acting on the stylus:
- the driving force, coming from the diamond tracking a rotating, modulated groove, say at freq. f; this force is the source of all the energy flows- the restoring force of the suspension- various damping forces, including the electromagnetic one ~f/R

In a word, yup.

The only *qualitative* change in R can happen is in the 1st, spurious part. Lowering the R changes the suspension character from underdamped to critically damped to overdamped. But this is not the signal we are trying to get! This is an artefact added to the real signal of freq. f.
Of course if the motor is so weak that the stylus tracing a HF track into low R will make it slow, we are in trouble but let's assume a healthy TT design.

Since we have been in agreement all along on the first two bits, maybe its this last bit that is the stumbling block. I used to load MM cartridges to critical damping by simply ringing the cartridge/cable combination with a square wave and observing the resultant output and taming it with a loading resistor. MM cartridges have a lot more inductance so its easy for that inductance to ring. But attempts to do this with LOMC failed, simply because with any loading I could not detect anything other than a nice looking square output since the inductance is so low. So I am challenging the idea of critical damping of the mechanical aspect of the suspension, not because I don't think it can happen but more because I'd like to see the evidence. Its an interesting idea- I am assuming that the electrical damping used to do this is similar to a shock absorber in a car; with the right amount the stylus in better contact with the groove, just like a shock absorber keeps a wheel on the road.


My exposure to all this is through phono preamplifier design; about 35 years ago I discovered that the phono section itself can contribute to ticks and pops. I discovered this serendipitously but once I understood it was real it was then a matter of sorting out why.  And the answer (as I have mentioned earlier on this thread) has a lot to do with this ultrasonic/RF resonant tank circuit that I've been talking about. I've also noticed that while I can cut a 35KHz groove on my Scully lathe, depending on loading you can't always play it back, depending also on the cartridge.


So now I am curious- at what frequencies did you make your measurements?  At this point it appears that the taming of the resonant peak requires a different value as opposed to that which might tame the cantilever; the two aspects are caused by entirely different mechanisms. However, **any** resistance in parallel with a tank circuit will detune it; for most phono sections to be happy the detuning must be enough to kill the tank circuit altogether.

I have no doubt that an unstable phono will have problems with spurious HF info but I do not see the cartridge ever generating anything in the megahertz realm to excite this.

I do not see anyone debating that a loaded MC cartridge will stiffen its suspension,

The cartridge will not generate MHz output. But think about it this way- if that resonance is out there and it never goes into excitation, this conversation would be moot. But obviously it does and here we are.
Raul has been challenging me on the stiffer cantilever thing. So I think we have to get past that first.
You can certainly run a cartridge into a near dead short. Its output will lower of course. But now that you point this out, the reaction by the cantilever would seem to be a downside. What is needed right about now is some sort of measurement, perhaps a sweep tone from 20 to 35KHz so we can play a cartridge back and see how the loading affects it. 35KHz is probably overkill but should be well within any modern LOMC cartridge and phono section. Its been on the record side for decades if my Westerex 3D is any indication. But to my knowledge other than conversation with others in the industry and my own research on the matter (I attempted to design a loading box that would sort out the correct loading for any cartridge about 20 years ago) I've not seen any actual measurements. Its for dead sure that stiffening the cantilever will have adverse effects in some situations, but in some cases it could help. One example of that is a Grado cartridge on a Graham 2.0 unipiviot. Normally the mismatch between the two results in something called the 'Grado dance'. But I've seen that with loading this dance is eliminated.

I for one would love to see documentation of the ability of a cartridge to generate a 1MHz signal to excite this resonance.

Quite simply it does not need to! Audio energy can cause the excitation. A resonant circuit can be driven into excitation with a single pulse; it should be no surprise that on-going audio signals can do this as well.

Dear @atmasphere and friends: "" and as I mentioned earlier, when you load the cartridge it stiffens the cantilever. ..""

"" It will be stiffer, less compliant. """

both statement from you failed for something very simple: no explanation about, no explanation why that: less/limited ability to trace high frequencies by the cartridge.

I would have thought that the reason for the reduced compliance (stiffer cantilever) would have been obvious! A cartridge is a simple magnetic motor/generator, just like a dynamic microphone or loudspeaker, in that a coil has an audio signal transduced into it by a magnetic means- either by moving the magnet with relation to the coil (MM) or moving the coil in relation to the magnet (LOMC). It is easy to demonstrate this principle with a woofer of a loudspeaker with the grill removed (dynamic speakers operate on the moving coil principle of course). With nothing connected to the loudspeaker, simply depress the woofer cone and see how easy it is to move. Now short out the speaker terminals and do it again. You’ll find that the woofer has become much stiffer! This is exactly what happens with a cartridge as the modus operandi is identical.


As I mentioned earlier, if this were not to happen, a new branch of physics would thus come into existence :) because it would violate Kirchhoff’s Laws. The operating principle is similar to how motors and generators work so you can study them as well. In short, its impossible for a cartridge to drive a lower resistance load and *not* have a stiffer cantilever!

This is just a well known electromagnetic breaking force, proportional to the velocity of the movement (in turn proportional to the frequency) and inversely proportional to the R. It is just plainly ~f/R, like any other linear damping force. It adds to the total damping force, acting on the cantilever (the rest comes e.g. for the mechanical damping in the suspension). Lowering the R, just lowers the output across the entire spectrum but the nature of the output (its functional dependence on f) does not change at all. No additional damping of higher frequencies beyond the normal behavior of a damped oscillator. Just the damping coefficient increases.

I think you might be over-thinking this.

You got most of this right, right up until your conclusion. Think about a generator, one with no load and one with a load, which will be harder to turn? By your logic above (if I’m reading it right) somehow the loaded generator is easier to turn, which certainly isn’t going to happen. I think where you’re getting into trouble is the idea that the output goes down with reduced R load, which it does. The problem is: a certain amount of energy is used to make the stylus move. Where does that energy go? It is of course applied to the input load of the preamp in the form of a voltage. Now if you decrease the voltage by reducing the R load value, where is that same energy going? The Law of energy conservation says it has to go somewhere! It does not just ’vanish’. It is dissipated in the load and also by the cartridge coils themselves, both in the form of heat. But I think you will find if you do some measurements that the output does not go down as fast as it appears you are thinking. This is because the stock 47K load is easy to drive and the output of the cartridge will stay pretty constant until the load is decreased to some point below 10x the impedance of the cartridge; IOW probably less than 100 ohms.

What I am interested in is the underlying explanation why a cartridge doing more work will necessarily have this "limited ability to trace higher frequencies"

It will be stiffer, less compliant.

Ralph, how does cartridge impedance affect all of this? I assume on a good phono amp not at all. If a higher load increases the motor's stiffness why wouldn't a cartridge track better at lower loads?

When one **increases** the load, the actual load resistance is lower. If there is less load, the resistance is higher.  That should answer your second question as well.

Is there a measurement on Stereophile or whatever that will show if a phono stage has resistance to RFI and/or good internal stability?

Otherwise the only way to know is to compare the sound of a LOMC at say 300 ohms vs 47k, right?

I've not seen Stereophile do any such measurements- which IMO suggests that whomever is doing the testing isn't paying attention to this parameter. So yes, trying the two different loading values is about the only way you can do it.


BTW, here is an excellent tutorial on this topic:http://www.hagtech.com/loading.html

This tutorial is seeing everything from the cartridge point of view and ignores how the phono section responds. But the resonant peak I've mentioned is obvious. Cartridge manufacturers often suggest a value for loading, but that is usually a general value and this calculator reveals why: the tone arm interconnect cable is playing a role (as well as the input capacitance of the phono section) and this value is an unknown. So the loading value often seen in the literature for a cartridge is really only a suggestion.


What I am maintaining is that if the preamp is properly designed, the resonant peak will be of no consequence to the phono section. Its pretty obvious that a peak like that if driven into excitation (which it often is by the cartridge itself) has the ability to overload the input of a phono section unless that phono section takes this issue into account.


Again, the presence of RFI or ultrasonic energy at the input of an active circuit can affect the way it sounds. As I mentioned earlier it can also affect the compliance of the cantilever of the cartridge. Jonathan Carr (of Lyra fame) and I had a conversation on this topic at Munich a few years ago- it was after a thread on this topic on which we were both active as on the What's Best Forum. He pointed out to me this issue of compliance- prior to that I'd not really thought it thru. Its a really good point because into 47k the cartridge might be doing X amount of work, but into 100 ohms it will be doing 470X **more** work, and that energy has to come from somewhere otherwise a new branch of physics is created :)

That of course will limit the ability of the cartridge to trace higher frequencies. But cartridge compliance is not measured with such low resistance loads, so when looking at the specs to see if a particular cartridge is going to work in a particular tone arm this issue can throw off the setup!

I run my Benz Wood SL "unloaded" at 47K on my Pass XP15. It sounds the most open, with airier highs, but admittedly I'd be hard pressed to tell the difference between 47K and 1000 ohms, maybe even 500 ohms. Seems the Pass XP15 just isn't that sensitive to loading.

You are correct- when I've pointed this stuff out on other threads, Pass Labs phono section owners respond as you have.

I don't understand this comment... a Manley Steelhead is unstable? The Steelhead lets you switch loading on the fly and the tonal differences were easily audible.

If the loading is affecting the sound like that its a good bet that the phono section is sensitive to the resonant peak' RFI as I mentioned earlier. Now I should point out that MM cartridges do behave differently- if you have one of those then loading is critical IME moreso that LOMC. This is partially because MM cartridges do ring at audio frequencies if not critically damped. LOMC cartridges don't ring anywhere near audio frequencies- if you 'ring' them with a square wave the input and output waveforms look the same.


There are IMO/IME four parameters that have to do with phono preamp design:
1) enough gain with low enough noise2) accurate EQ3) resistance to RFI4) good internal stability
It is the last two on the list where many phono sections have problems. If you find for example that you get lots of ticks and pops even with new vinyl, this is a sign that the preamp has troubles with these last two parameters. Needing to have a low resistance load on the cartridge is another (keeping in mind that we are talking about LOMC); if the phono section is set up right 47K as a load will be found to work just fine, assuming that normal low capacitance phono cables are in use.

The Zu Denon is very much a "salt to taste" kind of cartridge when it comes to loading. When I used one it could indeed sound quite different when using 100/200/300/500/1000 ohms. And Zu will tell you there is no wrong answer here, just use what sounds best to you

Again: loading has no effect on the sound of a **low output** cartridge- it has everything to do with the stability of the phono preamp.

@intactaudio While I agree generally with Peter in this regard, I am suspect of the idea that loading causes the cartridge to track better in all cases. I have seen this where the cartridge was otherwise incompatible with a tone arm; a good example is a Grado in a Graham 2.0. The loading prevents the 'Grado dance' that can otherwise occur especially in lead-in grooves. However that is all about tone arm compatibility, and as I mentioned earlier, when you load the cartridge it stiffens the cantilever. So you will get different results in different tone arms! Peter wasn't being entirely scientific in this regard as his data was limited to one tone arm/cartridge combination.

@stereo5 47K is the standard for phono cartridge loading. 

I am very happy at 1K ohms, I was just kind of wondering why.

I explained why in my prior post. With a higher impedance load on the cartridge, the cantilever is more able to trace high frequencies.

Cartridge loading is for the benefit of the phono section, not the cartridge!

It prevents the inductance of the cartridge and the capacitance of the tone arm interconnect cable from creating a resonant circuit, by detuning it. The resonant circuit can produce noise (often RFI) that is considerably more powerful than the cartridge signal itself!


The problem is that the loading resistor also causes the cartridge to do more work- it has to drive that load. The energy to do that comes from the stylus in the groove driving the magnetic generator in the cartridge, so the cantilever will get stiffer and less able to trace high frequencies.

So less loading will open up the highs in some cases. The problem is if the circuit resonance appears, it acts as RFI injected into the input of the phono section. If the phono section is sensitive to RFI it won't sound right- hence the need for loading. OTOH if the phono circuit designer understood this problem, then no loading at all is needed since the phono section will have no problem with the RFI. A side benefit of a proper phono preamp design is you will also experience less ticks and pops, as these can be caused by stability problems in the phono preamp!


At any rate always go with the least loading (highest resistor value) you can such that the system has correct tonal balance.