MC: Aim for lowest possible capacitance and highest possible resistive loading
I wanted to expand a bit on JCarr's research seen back in post #32 http://www.whatsbestforum.com/showt...ing-A-Misnomer&p=258578&viewfull=1#post258578 and why we should aim for lowest overall capacitance for the possible highest resistive loading (for MC), and the following are excerpts from my conversations with JCarr, and since he's a very busy man I got permission to share with you (and I wouldn't be posting his comments if I were not in complete and utter agreement, as per numerous previous posts in years past). BTW, what a gentleman to share his research and spend the time and go into such detail!
The following consolidate what's been previously discussed in this thread and other comments across other threads regarding current flowing through the cartridge's coils.
JCarr:
Resistance is one of those things that is easy to mis-construe unless everyone discussing the topic is very clear (even verbose) with the terminology. Higher capacitance values should be paired with lower resistance values, and vice versa.
The loading resistor value is placed across the phono cartridge's output terminals, which means that any output voltage produced by the cartridge will be forced to flow through the load resistor in the form of current. The higher the load resistor value is, and the farther the net impedance is from the cartridge's internal resistance, the less current will be produced. Conversely, the lower the load resistor value is, and the closer the net impedance is to the cartridge's internal resistance, the more current will be produced.
Forcing the cartridge to produce more current works it harder, and in so doing, stiffens the compliance (the cantilever moves less readily). Making the net impedance closer to the cartridge's internal impedance (by using lower-value load resistors) will also attenuate the voltage output from the cartridge, which makes the job of the phono stage (the vast majority of which are voltage amplification devices) harder.
IMHO, the only time that forcing the cartridge to produce more output current could be justified is when using it into an IV phono stage. Since this kind of phono stage converts input current into output voltage (and is more or less oblivious to input signal voltage per se), it would make sense to feed an IV phono stage with as much input current as possible. An IV phono stage, however, possesses de facto a low impedance input node that receives the output current from the cartridge as a series element (without needing a separate load resistor). This is not how a normal loading resistor works with a typical voltage amplification stage, since there the separate load resistor bleeds the current from the cartridge into ground (thereby wasting that energy). Also, IV phono stages sound qualitatively different to voltage amplification phono stages., and part the reason is that undoubtedly the cartridge is forced to operate into a zero-ohm load (or some other values that is quite close to the cartridge's internal resistance).
IME, a phono cartridge provides the highest resolution and widest dynamic range when the phono stage load resistance is of as high of a value as possible (10kohm rather than 100ohm). Realistically too high load resistance values will force the phono stage into distress due to insufficiently damped and too-large levels of ultrasonics and frequency peaking [ack: refer to research in post #32], so practical load resistor values need to be a compromise between a value that is low enough to keep out of the phono stage's danger zone, while loading the cartridge as little as possible. The reason why less capacitance in the tonearm cable is an advantage is that doing so allows the use of higher load resistance values at the phono stage input.
Note that the above only applies to low-impedance cartridges (mainly MCs). Cartridges in which the electrical impedance is quite high within the audible band tend to be treated differently, with the electrical load being used to deliberately equalize the cartridge's audible frequency response.
[ack: Regarding the Hagerman calculator http://www.hagtech.com/loading.html, which it tells me my optimum value would be around 300ohms]:
No calculator can tell you what the optimum setting is, since the optimum load is a compromise between a resistive value that is low enough to keep your particular phono stage away from its danger zone, while loading the cartridge as lightly as possible [keep in mind that lower resistance value means "heavier resistive loading" , while higher resistance value means "lighter resistive loading"]. Different phono stages have different tolerances to overload and RF, so a resistive value that may be optimal for one phono stage may not be suitable for another.
And although the reactance between tonearm cable and cartridge coil inductance creates a spike in the frequency response (with attendant severe impact on the phase response), this does not create new energy - it only amplifies whatever is present in the local electrical environment. If you live in the countryside, you may be able to use a higher resistive value for loading than a city-dweller. However, even if you live in the countryside, if some electronic component in your house is producing RF, this could preclude you from using higher resistive values for loading.
I wanted to expand a bit on JCarr's research seen back in post #32 http://www.whatsbestforum.com/showt...ing-A-Misnomer&p=258578&viewfull=1#post258578 and why we should aim for lowest overall capacitance for the possible highest resistive loading (for MC), and the following are excerpts from my conversations with JCarr, and since he's a very busy man I got permission to share with you (and I wouldn't be posting his comments if I were not in complete and utter agreement, as per numerous previous posts in years past). BTW, what a gentleman to share his research and spend the time and go into such detail!
The following consolidate what's been previously discussed in this thread and other comments across other threads regarding current flowing through the cartridge's coils.
JCarr:
Resistance is one of those things that is easy to mis-construe unless everyone discussing the topic is very clear (even verbose) with the terminology. Higher capacitance values should be paired with lower resistance values, and vice versa.
The loading resistor value is placed across the phono cartridge's output terminals, which means that any output voltage produced by the cartridge will be forced to flow through the load resistor in the form of current. The higher the load resistor value is, and the farther the net impedance is from the cartridge's internal resistance, the less current will be produced. Conversely, the lower the load resistor value is, and the closer the net impedance is to the cartridge's internal resistance, the more current will be produced.
Forcing the cartridge to produce more current works it harder, and in so doing, stiffens the compliance (the cantilever moves less readily). Making the net impedance closer to the cartridge's internal impedance (by using lower-value load resistors) will also attenuate the voltage output from the cartridge, which makes the job of the phono stage (the vast majority of which are voltage amplification devices) harder.
IMHO, the only time that forcing the cartridge to produce more output current could be justified is when using it into an IV phono stage. Since this kind of phono stage converts input current into output voltage (and is more or less oblivious to input signal voltage per se), it would make sense to feed an IV phono stage with as much input current as possible. An IV phono stage, however, possesses de facto a low impedance input node that receives the output current from the cartridge as a series element (without needing a separate load resistor). This is not how a normal loading resistor works with a typical voltage amplification stage, since there the separate load resistor bleeds the current from the cartridge into ground (thereby wasting that energy). Also, IV phono stages sound qualitatively different to voltage amplification phono stages., and part the reason is that undoubtedly the cartridge is forced to operate into a zero-ohm load (or some other values that is quite close to the cartridge's internal resistance).
IME, a phono cartridge provides the highest resolution and widest dynamic range when the phono stage load resistance is of as high of a value as possible (10kohm rather than 100ohm). Realistically too high load resistance values will force the phono stage into distress due to insufficiently damped and too-large levels of ultrasonics and frequency peaking [ack: refer to research in post #32], so practical load resistor values need to be a compromise between a value that is low enough to keep out of the phono stage's danger zone, while loading the cartridge as little as possible. The reason why less capacitance in the tonearm cable is an advantage is that doing so allows the use of higher load resistance values at the phono stage input.
Note that the above only applies to low-impedance cartridges (mainly MCs). Cartridges in which the electrical impedance is quite high within the audible band tend to be treated differently, with the electrical load being used to deliberately equalize the cartridge's audible frequency response.
[ack: Regarding the Hagerman calculator http://www.hagtech.com/loading.html, which it tells me my optimum value would be around 300ohms]:
No calculator can tell you what the optimum setting is, since the optimum load is a compromise between a resistive value that is low enough to keep your particular phono stage away from its danger zone, while loading the cartridge as lightly as possible [keep in mind that lower resistance value means "heavier resistive loading" , while higher resistance value means "lighter resistive loading"]. Different phono stages have different tolerances to overload and RF, so a resistive value that may be optimal for one phono stage may not be suitable for another.
And although the reactance between tonearm cable and cartridge coil inductance creates a spike in the frequency response (with attendant severe impact on the phase response), this does not create new energy - it only amplifies whatever is present in the local electrical environment. If you live in the countryside, you may be able to use a higher resistive value for loading than a city-dweller. However, even if you live in the countryside, if some electronic component in your house is producing RF, this could preclude you from using higher resistive values for loading.
