Basically, a current source is characterized by a high (ideally infinite) output impedance which delivers a constant current regardless of load impedance. A voltage source is characterized by a low (ideally zero) output impedance which delivers a constant voltage regardless of load impedance.
The voltage across a current source's output is determined by the load impedance as per Ohm's Law, E = I x R. The current through a voltage source's output is determined by the load impedance as per Ohm's Law, I = E/R.
A current source prefers to see a low (ideally zero) load impedance while a voltage source prefers to see a high (ideally infinite) load impedance.
So as you can see, current sources and voltage sources are essentially the inverse of each other.
Some feel that the output of an MC cartridge is best characterized as a current source. So to that end, it is argued that an MC cartridge should ideally drive a short circuit.
While the manufacturer's comment refers to the MC inputs of the AQVOX as a "current amplifier," others (especially those who have played around with DACs) may be more familiar with the term current-to-voltage or I/V converter.
If you take an opamp, and configure it as an inverting amplifier, its "-" input acts as a virtual ground, i.e. a short circuit which is what the current source wants to see, and the opamp outputs a voltage that's proportional to the current flowing through its "-" input.
That's essentially what's being done here. The 47 Labs Phono Cube also uses this method. And there are those who feel that the primary job of an MC step-up transformer isn't so much to provide signal amplification as it is to present the MC cartridge with a much lower load impedance and act in a sense as a passive current-to-voltage converter.
This help?
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