SUT - electrical theory and practical experience

@rauliruegas 

You quote another post above: “A phono cartridge is a voltage generator (Vs)”

To me, that sounds like a premise, and from my very limited knowledge base, it sounds like it could very well be a false premise, as phono cartridges generally produce very low voltages, which would imply that they are indeed better classified as current generators….

if that’s the case, then all conclusions based on that premise are also potentially false.

Dear @drbond  : Then you can ask him directly, here is his post:

R.

You can go to this link and there to marketplace feedback and that's it:

R.

rauliruegas 

You quote another post above: “A phono cartridge is a voltage generator (Vs)”

To me, that sounds like a premise, and from my very limited knowledge base, it sounds like it could very well be a false premise, as phono cartridges generally produce very low voltages, which would imply that they are indeed better classified as current generators….

if that’s the case, then all conclusions based on that premise are also potentially false.

well done @drbond you are onto something important here.

Wiki says…

…or conversely, an external time-varying magnetic field through the interior of the coil generates an EMF (voltage) in the conductor.

However… the wiki for Maxwell’s equations says, (under Ampere/Faraday)…

The original law of Ampère states that magnetic fields relate to electric current. Maxwell's addition states that they also relate to changing electric fields, which Maxwell called displacement current. The integral form states that electric and displacement currents are associated with a proportional magnetic field along any enclosing curve

That link to displacement current says:

In electromagnetism, displacement current density is the quantity ∂D/∂t appearing in Maxwell's equations that is defined in terms of the rate of change of D, the electric displacement field. Displacement current density has the same units as electric current density, and it is a source of the magnetic field just as actual current is. However it is not an electric current of moving charges, but a time-varying electric field. In physical materials (as opposed to vacuum), there is also a contribution from the slight motion of charges bound in atoms, called dielectric polarization.

Hence I think that Raul could be correct.

While I was pretty sure that a cartridge is a current generating device, I am not so sure anymore.

The statement of, “a time varying electric field” also explains why a transformer voltage does not vary much with load.

A speaker and a cartridge are not too dissimilar.
If we consider a speaker, and yell into it, then the movement of the cone, generates a movement of the voice coil, and a change of how it sits in the magnetic flux of the motor. And if we are hoarse we can push it with a finger tip.

• if it was generating a voltage:
  • then when the speaker terminals are open, there is no load against the voltage, and whether we push on the cone with a finger or thumb, it should move freely.
  • And if we put a 2 ohm resistor across the speaker terminals then that voltage will need a lot more current as it moves, and the speaker should feel stiffer to the finger tip.  
• if it is a current generating device then:
  • The movement will generate a fixed current and in a shorted speaker it should easily pass the fixed current and the cone should feel limber
  • and with an open set of speaker terminals, then the cone will be trying to drive current into an infinite load and require the voltage to rise towards infinity and the speaker cone should feel stiff.

Dear @holmz  : I was in a hurry when my post to op but I gone thinking that's the whole context what is behind what Palmer posted.  He participated in that technical loading thread that after some posts took other road.

I can't remember but I think that in other threads you and he had a very interesting technically posts.

R.