The sensitivity of the C-meter
is closely matched to that of the original British Mk5. With the sensitivity
booster set at 2 the range 1 to 32 corresponds closely to the physical scale
of the Mk5 rather than the numbering. The sensitivity control of the C-meter
has been arranged so that a given numeric increase in sensitivity will produce
the same percentage change in actual gain. The sensitivity booster positions
3 and 4 correspond to 64 and 128 on the Mk5. With the booster set at 1 and
the sensitivity at 1 a 360° scale corresponds to the full range of TA.
The following table shows the extra 3 options for gain available in the C-meter.
The sensitivity is modified according to the TA by being multiplied by factors
gain1, gain2, or gain3.
Calculations are based on a standard Wheatstone bridge with a 21250 ohm
bridge resistor using a voltage range from -1 to 1.
Column 1: Tone arm position.
Column 2: Corresponding resistance in ohms per the formula TA = PC/(PC
+ 21250)*5.55882353 + 0.94117647
Column 3: Voltage change in the bridge for a 1% resistance change.
Column 4: Additional gain needed to increase the sensitivity to make the
needle response equal for percentage changes in resistance independent of
TA.
Column 5: Voltage change using gain1.
Column 6: Additional gain needed to increase the sensitivity to make the
needle response equal for equal value changes in resistance independent
of TA.
Column 7: Voltage change using gain2.
Column 8: Modified gain to compensate for reduced sensitivity at low TA
using gain2. It selects the greater value of gain1 and gain2.
Column 9: Voltage change using gain3.
The factor used by the CofS Quantum appears based on an algorithm similar
to gain2.
