Cartridge Loading.....Part II

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.

Dear @wynpalmer4 : I understand you but due that some gentlemans as lewm just did not reads the whole cartridge loading threads then are reduntdant on the issue one and again and other gentlemans what want is to " win " the discussion or " hit " to some one else and of course always exist the stupid and the stupidity.

. Sorry that disturb you and sorry for what I will posts next.

 

R.