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.
