And LPspinner agreed and reinforced his view:
LPspinner wrote: Yes quite right lfleib. I fail to see the advantage of using a balanced input for a phono stage when nearly all phono cartridges use a single coil for each channel and therefore unbalanced by nature.
While I will agree that that a phono cartridge can be configured to work into a balanced input if you wire the coil outputs across the Positive “Hot” and the Negative “Cold” balanced inputs and leave the coils to float above the earth potential but I fail to see how this configuration offers the advantage of a true dual signal “balanced” complementary voltage source that allows cable borne interference to nulled out when the complementary signals are summed at the input end of the pre-amp or phono stage. To my mind this is the only reason you would bother with a balanced configuration in the first place.
Also consider that Most Moving magnet cartridges will have one end of their coil assemblies earthed to the metal cartridge body in order to shield the coil assembly from noise and the effects of the outside electrical environment. This arrangement makes the “float above earth” quasi-balanced configuration no longer achievable.
Low output Moving Coil cartridges are a different case altogether, due to their very low source impedance (usually less than 10 turns of wire around the armature), the Moving Coil cartridge will act as a curent source rather than a voltage source and because of the low impedance most noise generated within the cable will be shorted to earth.
As a side issue it is also worth pointing out that with Moving Coil cartridges most noise issues are generated within earlier amplification stages due to the high levels of gain required and not from in noise induced into the cable form an electrically noisy environment for the same reasons listed above. However these days internally generated noise issues are no longer an issue as modern electronics will easily provide very quiet Moving Coil head amps.
I think here we are confusing two different conditions when it comes to our discussion about balanced configurations. Steerpike_jhb is talking about the impedance matching conditions and considering the cable transmission system as a “transmission line” in order to optimise the curent and voltage relationships within that transmission system and from this perspective his theory is quite sound and valid. I would consider this type of balanced operation as an “impedance-balanced line”
In the situation I am considering as balanced I am referring to the fact that two symmetrical voltages are required with respect to an earth or Zero potential in order to cancel, null, or balance out induced interference within a cable carrying a signal. As I said above most Moving Coils have an output impedance that approaches zero, so in my book considering this as an “impedance-balanced line” doesn’t seem quite right, at least not without introducing a transformer or impedance matching head amp at the cartridge end.