Cartridge Loading.....Part II

I didn’t mention a dead short and was only referring to the two terminal impedance the coil of a cartridge sees. Any reference to ground be it real or virtual does not factor into the load seen by the coils. Surely there has to be an actual input impedance for a current amp and it has to be low otherwise the coils will not generate any current to amplify.

Do you see how this above does not jive with this:

that depends on what load the input of the following stage gives.

If it is a voltage amplifier with 47kΩ, a 30Ω cartridge loaded by 5Ω it will be 17dB down.  When you replace that 30Ω cart with a 2Ω cart the output will only be down 3dB. If it is a current amplifier with a 1Ω input impedance a 5Ω parallel load will lower the current into the 1Ω input node by1.6dB with both the 2Ω and the 30Ω cartridge. The absolute currents will be different for the 2Ω and 30Ω carts but the relationship of how the 5Ω load affects a 1Ω input impedance stays the same.

Transimpedance phono sections have a dynamic load whereas a resistor is a static load. This is because the so-called 'virtual ground' (which will be 0 Ohms) occurs where the feedback resistor of an opamp meets the input resistance, which in this case will the cartridge itself.

At any rate, Moncreif threw off his numbers by using a 5 Ohm load, since that is not only not a real-world value that no-one would ever use, but is also one that would significantly decrease the output of any LOMC cartridge to the point that its output would be unusable (which is why its not real world...). Keep in mind that transimpedance phono sections didn't exist back then. As I mentioned previously, if he really wanted to make his point valid he needed to show the results using real world loads that are actually in use.

That laST POST IS PART OF THE WHOLE REGARDS STUPIDITY COMING FROM THE SAME PERSON, COMING FOR HIS FRUSTRATION .

@intactaudio  audio " falls " in that person game ( because intactaudio in good faith gentleman unknow that person game. ) that when he can't win then he follows been argumentative and goes " around and around "  with different issues than the one under discussion ( exactly like here. ) makind a way deviation from the main subject.

I followed his " game " when he already bbeated and I did it for many years till I learned.

That's why JC just does not  follows that stupid game and never suported him with the IMD issue discussed for years.

Please look to what stupid levels goes his stupidity:

""" At any rate, Moncreif threw off his numbers by using a 5 Ohm load, since that is not only not a........., if he really wanted to make his point valid he needed to show the results using real world loads that are actually in use. "

Certainly it's not PM who should do that  because PM shows at 100 ohms too but more important : that stupid man not only does not shows nothing/measures to prove his point but now he ask that the gentleman that measured and proved that the IMD is developed by the cartridge loading effect still makes more measures: GO FIGURE ! ! !

Yes, in our world exist any kind of stupidity we could think.

R.

Now, now... let's try and keep it civil.  I've enjoyed the discussion this far and am impressed by many members knowledge base.  Which is very helpful to the lion's share of members!

Ralph,

The two statements you quoted from me seem to align well with each other and I was unaware that there was a different versions of ohms law for static vs dynamic loads

At any rate, Moncreif threw off his numbers by using a 5 Ohm load

I agree it is an interesting choice but his measured results clearly show signal and if  if anything a lower noise floor so I fail to see where the issue is or how it invalidates his results.

dave

The two statements you quoted from me seem to align well with each other and I was unaware that there was a different versions of ohms law for static vs dynamic loads

At any rate, Moncreif threw off his numbers by using a 5 Ohm load

I agree it is an interesting choice but his measured results clearly show signal and if if anything a lower noise floor so I fail to see where the issue is or how it invalidates his results.

In the case of a transimpedance input, feedback is applied to the output of the cartridge. Its a fair amount of feedback too- the more output the cartridge has the more feedback. That is quite a bit different than a simple resistor- you can’t equate a virtual ground with a static resistance- for one thing, you need an opamp to even create a virtual ground.

Ohm’s Law certainly is in play (how could it not be), but the issue here is that while a cartridge has its output at a virtual ground, that is significantly different from having the cartridge drive 0 Ohms (IOW, if it were actually tied to ground). In the case of the former, the actual input impedance is dynamic and isn’t actually 0 Ohms, so amplification can occur because a signal is present. In the case of the latter, the load is actually a short and because the signal is shorted out, no amplification can occur.

’Virtual’ means ’almost or nearly as described, but not completely or according to strict definition.’ If the 0 Ohms of a virtual ground is conflated with the 0 Ohms of actual ground, confusion is the direct result.

Real ground is when a terminal is connected physically to the ground or earth, whereas virtual ground is a concept used in opamps in which a node is assumed to have the potential that of the ground terminal.

 

I say Peter threw off his numbers because he chose a value that no-one would ever use (and a static value at that, no opamp involved, so the load was causing the output of the cartridge to change in a significant way, whereas real-world loads have negligible effect) since its a reasonable expectation that if you are going to use a load on a cartridge, you’d likely start with one that is 10X the source impedance of the cartridge.

I can see using static values lower than that, but not one that’s actually lower than the the source impedance! Barring a good explanation for that, when I read that in his article I found I simply had to take his results in abeyance. I’d have to read the article again (Google defeated my attempts to locate it just now), but IIRC he had some variables left uncontrolled that I felt at the time might affect his results.

One way around this is to ignore that transimpedance inputs exist and simply focus on what happens to the output of any source when the load is a fraction of that of the source. That’s really what I’m getting at here, if Peter was actually suggesting that we use such loads both back then and now the extra gain needed would be impractical.