loading, back emf and damping

[Ldg]

Hmm so presumably non linearities due to eddy current could be reduced by lamination of the MC magnetic circuit components (which effectively form a core!) - same as for MM's

You miss the point, that materials selected for being magnetically 'hard' for strong permanent magnets generally have high hysterisis, and other poor properties to make cores. Notwithstanding whether the permanent magnets are laminated to reduce induced eddy-losses, which is a totally seperate non-ideal effect. I'd guess generally not.

My reading also indicates that there would also be a hysteresis effect generated by the cartridge suspension - and presumably the higher the damping on the cantilever, the higher the hysteresis....
Another reason for high compliance (low damping) cartridges?

No, that's total nonsense. 'Hysteresis' in a totally different (mechanical) context. Off topic, and highly disputable anyway. Suggest start another thread, DL.

I'm still trying to grasp what components of a transformer / cartridge design reduce hysteresis effects.

Mostly, it's a material property. Varies significantly between high permeability materials. But also depends on 'bias', or where one is on the B-H curve.

[Rothwellaudio]

I'm just curious and always trying to gain a deeper understanding of what I'm doing so I can do it better.

Thanks, Rothwellaudio. I empathisize because that's my philosophy too. I always like to run out of questions before running out of answers.

I think the permanent magnetic circuit may be in play, even for an air cored MC.

As previously posted, one way of looking at is as though the source of flux change is a perfect primary of a transformer. And the MC coil is a real secondary winding, which sits in an (air) gap. Here's a sketch which shows the permanent magnet loop (yellow), and the MC coil. Plus a source of flux changes.



One can see that, proximity and geometry permitting, changes in MC coil flux [inc back emf/loading effects] are mostly conducted by the permanent magnetic circuit. For example, self inductance of the MC coil is determined (potentially significantly) by the permanent magnet circuit. And, being highly permeable, influenced by the non ideals therein.

From a back emf and loading point of view, I think the permanent magnetic circuit is effectively a core, even if the coil is in an air gap.

In any event, using this sketch model, one can evaluate an MC cartridge as a transformer. Albeit a strange one, with high leakage inductance, and potentially significant non-ideals.

I'm a bit confused by the mechanical movement induced flux changes. Surely the flux in the permanent magnet could remain absolutely rock solid and the cartridge would still work as long as the coils move through the flux in the air gap. What mechanical movement would affect the flux, other than the coil's motion and the current flowing in the coil?
Yes, I can see that if the flux was modulated by something, the coil would pick it up as a signal. But what could be modulating the flux?

[Ldg]

........Surely the flux in the permanent magnet could remain absolutely rock solid and the cartridge would still work as long as the coils move through the flux in the air gap.

Yes, if there is no coil (load) current. Otherwise Lenz's law applies, and a flux change in the permanent magnetic circuit is induced by load current. I think.

........What mechanical movement would affect the flux, other than the coil's motion and the current flowing in the coil?

From the MC coil point of view, flux change is the same whether it is due to motion, or due to a virtual 'perfect primary winding' inducing flux changes to modulate the permanent field in which it sits. By 'perfect', no losses or non-ideals is implied.

But actually, the source of flux changes isn't important. It is the reaction, and flux circuit non-ideals associated with 'secondary' load current that is at issue. Again, i think.

I see your point, Rothwellaudio. The 'perfect primary winding' is a poor analogy, perhaps. That's often the nature of analogy, unfortunately.

Forget the analogy. If one measures impedance of the MC coil, (inductive reactance and total loss) is it influenced by the permanent magnetic circuit ? I venture yes, because it's typically part of the coil's magnetic circuit. And therefore is potentially subject to it's non-ideals.

[Rothwellaudio]

I've had another thought. The coils in a MC cartridge are usually wrapped round a small former. If the coils aren't totally rigid, they will be subjected to physical forces as they pass current, causing them to deform or vibrate at a microscopic level. Energy which is going into changing the coils' shape is being robbed from the electrical system. Drawing more current from the coils by having a lower load resistance will exacerbate the problem.

Again, just a thought, not a dogmatic declaration of a eureka moment.

[dlaloum]

Again, just a thought, not a dogmatic declaration of a eureka moment.

So we are not expecting pictures of you running down the street naked?

[Rothwellaudio]

Again, just a thought, not a dogmatic declaration of a eureka moment.

So we are not expecting pictures of you running down the street naked?

They're on my facebook page.