First, are you running directly into a gain stage or into a stepup? An MC feeding a tranny will want to see a much lower impedance than if it's directly feeding a gain stage. In addition, a tranny steps the resistance of the circuit down by the square of its turns ratio.

In either case and to answer your question, everything in the circuit affects the impedance seen by the cartridge, though this is far more audible with a tranny.

That said, I'd advise ignoring the answer! If you're just choosing an impedance by theoretical calculation, the impedance of any decent phono and tonearm cable should fall below the threshhold of concern. I'm not saying you won't hear a difference if you allow for them and choose a slightly different resistor. You will. It's just that the change will be so small that you can't predict - in advance - which overall impedance will sound best.

Cartridge manufacturers' loading guidelines are just that, guidelines. Fretting about getting to exactly 500 ohms, instead of 498.638 ohms due to the wire, isn't worth the bother. It's just as likely that 501.362 ohms will sound best in your system and room anyway. The only way to find out is to listen to it both ways.

If you insist on going nuts, the formula for calculating the combined value of multiple resistive loads in parallel is:

1/R = 1/ra + 1/rb ...

R = combined resistance

ra = resistance of resistor (or wire) a

rb = resistance of resistor (or wire) b

etc.

Using this formula you can actually combine two or more resistors to achieve intermediate impedance loads for which no single resistor is available.

In either case and to answer your question, everything in the circuit affects the impedance seen by the cartridge, though this is far more audible with a tranny.

That said, I'd advise ignoring the answer! If you're just choosing an impedance by theoretical calculation, the impedance of any decent phono and tonearm cable should fall below the threshhold of concern. I'm not saying you won't hear a difference if you allow for them and choose a slightly different resistor. You will. It's just that the change will be so small that you can't predict - in advance - which overall impedance will sound best.

Cartridge manufacturers' loading guidelines are just that, guidelines. Fretting about getting to exactly 500 ohms, instead of 498.638 ohms due to the wire, isn't worth the bother. It's just as likely that 501.362 ohms will sound best in your system and room anyway. The only way to find out is to listen to it both ways.

If you insist on going nuts, the formula for calculating the combined value of multiple resistive loads in parallel is:

1/R = 1/ra + 1/rb ...

R = combined resistance

ra = resistance of resistor (or wire) a

rb = resistance of resistor (or wire) b

etc.

Using this formula you can actually combine two or more resistors to achieve intermediate impedance loads for which no single resistor is available.