How does this affect the sound and what is the theory behind it?
Why don't the reviewers in TAS specify how they test the cartridges ?
Test conditions loading of transformers and resistors and effects on the sound
Well I think mostly because it is a case of stepping into quicksand!
With most MM/MI designs, there are 3 "plots" superimposed to generate your frequency response:
1) The base inductance / resistance / capacitance circuit which will limit frequency response and may generate an electrical resonance
2) The response of the cantilever and the location (frequency) of its mechanical resonance (in many higher inductance designs, well within the audio range)
3) The magnetic loss / non linearity (tendency for the cartridge core to be most efficient at lower frequencies and less efficient at higher frequencies) - this adds an additional downwards slop to the frequency response
All 3 can be identified and even modelled - but it takes time and effort....
With the base electrical loading - the end result can also be predicted (at least roughly) via modelling - but the differences in sound can be very very dramatic (+/- 20db on frequency peaks is easily possible)
I would love to see more details on cartridge loading - but I can understand why a magasine reviewer would limit himself to the "standard" (47k / 300pf for MM, 100 ohm for MC) - these are the settings that most people are using - regardless of whether they are optimal or not.
Most people do not have the gear to adjust loading in any case.
If you read some of the reviews of the 1970's they quite often had a paragraph or 2 on optimal loading in a cartridge review.
The ADC ZLM review I recollect had something along the lines of - If you plug it into a standard setup it will sound like a good cartridge, if you optimise the loading it then becomes a top class performer.
This is as true now as it was then - but seems to be ignored a lot more!
bye for now
Forget working out the correct loading for moving coil cartridges, the Aqvox phono preamp will do it for you, have a look :