Added an SUT...not sure I understood this

the industry standard of 47kΩ was adopted from the MM cartridge world and applied to the MC realm because is first and foremost "does no harm".... until you throw a SUT into the mix that is.  Once a SUT is added the load the cartridge can see can get vanishingly low to the point where you actually start losing gain as you increase turns ratio.

Most SUTs are meant to drive a 47,000 Ohm load since they are also built to work with a specific cartridge. Generic SUTs (like Jensens) might also be built to drive 47K although with some additional loading to allow it to express the turns ratio correctly with different cartridges (which have different source impedances). Some Jensen transformers are meant to drive lower impedances but IIRC that's still about 6.8KOhms.

Lets get back to the simple question I asked....  If going well below a cartridge manufacturers load is not recommended, how can we reconcile the use of transimpedance amplification or in your case a load that is 1.7X the cartridge internal impedance?

A transimpedance input is a special beast. It requires an opamp and when you set up an opamp circuit with feedback, you get something called a 'virtual ground' where the input signal meets the feedback signal. Its not actually ground ('virtual' means 'almost or nearly as described, but not completely or according to strict definition.'). This is why "virtually 100%" is not in fact 100%...

Anyway, in a transimpedance amp the cartridge is substituted for the input resistor. The significance here is that if the virtual ground were actually ground, the signal going thru the input resistor (or coming from the cartridge) would be snubbed at the virtual ground- the signal would stop dead. But it doesn't!

The lesson here is that virtual ground isn't in fact ground. Thus while its impedance might appear to be quite low, it does not function as if its impedance is actually that low. IOW it does not have all the qualities of an actual ground!

Its confusing yes, but in actuality the cartridge isn't driving an impedance that is at or near ground (which would be 0 Ohms or very nearly that). Its actually driving something quite a lot higher.

The gain of an opamp circuit is defined by the input resistor vs the feedback resistor. For example if the input is 100 Ohms and the feedback is 1000 Ohms, the gain will be 10. Since the cartridge is a variable source impedance from cartridge to cartridge, the gain of the circuit will vary from cartridge to cartridge too- more gain with a lower source impedance, less gain with a higher source impedance. This means the output will not vary that much as you change out the cartridge, but it also means that the circuit inherently has limits (due to the amount of feedback applied) and won't work with every cartridge.

Ralph...  we have been over this.  I made a point above to never mention ground and simply referred to the cartridge as a two terminal device feeding a two terminal load.   If the goal of that load is to maximize current draw then by necessity it must be low in value.  Since both Ohm and Kirchoff must be obeyed.... all of the current leaving one terminal of the two terminal cartridge must traverse the load and return to the other terminal.  The application of Ohm to this situation clearly defines all of the parameters at hand.

dave

You are correct in your conclusion, but IMO asking the wrong question.

I am the only one here asking the relevant question in this situation. This all goes back directly to the insistence that something was broken in your system if your cartridge sounds better with a 20Ω load.  The only question I asked (and has yet to be answered) is how does one account for the use of a load well outside a manufacturers recommendation (ie a current amplifier as an extreme example) and still adhere to the wishes of the manufacturer?

In your particular case I trust your assessment that the sound is good and suspect that anyone that insists otherwise based on a published spec is in error.  Who knows I may be he only one with this belief.... it wouldn't be the first time.

I did not  drag this off topic into how current amps differ from voltage amps, others took it there.  I really think this is a simple question that apparently nobody seems to have a good answer to.

dave

@intactaudio I misunderstood the intention behind your post then.

Unfortunately, the question you have asked has a rather uninteresting answer. Everyone on this thread has been assuming I determined that the best sounding load for my cart was a large deviation from spec, apparently because one participant loudly and repeatedly felt the need to insist I did not know how to read the instructions that came with my cartridge. I have attempted to clear up that confusion by asserting that my cart in fact has a 20 ohm spec, but apparently I don't know whatever secret handshake a person needs to know in order to be taken at one's word on these forums.

But none of that changes the fact that I am loading my cartridge at spec, which might render your question moot. I do agree with you, though, that if I achieved better sound at a different load than that recommended, I would use what sounds best.