6
Cartridge Selection
The selection for best performing moving‐coil cartridges changes if, instead of a conventional voltage
amplifier input, a current‐injection input proceeds the signal.
One difference is the much higher electro‐magnetic damping of the CI input, controlling cartridges with
less mechanical damping. Simultaneously, the outstanding electro‐magnetic damping of the cartridge is
not at the expense of dynamics ‐ on the contrary: The current withdrawn from the Moving Coil is used
as the original music signal.
The output voltage of a pickup is not the only criteria for the expected volume and dynamics. Only in
correlation with the internal impedance of a Moving Coil, the corresponding current can be calculated.
Although due to different measurement methods, not perfectly comparable values, but a trend can be
clearly seen, as long as both electrical parameters are available: The output voltage of a pickup as well
as its internal resistance.
Based on Ohm's law the signal current can be calculated:
V : (Rmc + Rin) = I
V
= defined output voltage
Rmc
= internal resistance of the MC cartridge
Rin
= input resistance of the phono amplifier
I
= signal current
On the low side some MCs deliver 10μA or less, under CI‐Input conditions.
A wide middle range of cartridges deliver between 10 and 30μA.
High efficient Moving Coils exceed 30μA, some models deliver up to 100μA.
Extremely high efficient Moving Coils may need individual gain settings inside of BMC PHONO MCCI,
which is an easy job for any authorised BMC Service.
Phono amplifiers with current input stage are still rare, therefore some MC manufacturers didn't consider
the MC's efficiency so much. Nevertheless in recent years several brands did increased efforts of
improving their cartridge's efficiancy, due to significant quality improvement.
