Long XLR's: PAD Venustas versus Mogami

Al, maybe I had it reversed?

I run 5 meter pair of purist dominus (updated) in XLR and also have mogami. My einstein preamp have very low output imped for tube preamp. The Dominus sounds a lot better than Mogami. Mogami sounds opague with closed in treble and lacked detail. I also compared the Venustas in 2 meter config and they are better than Mogami as well. I was hoping the Mogami would equal the purist so I can save some cash. this was not the case.

I recently have great results with Cardas bulk tonearm cable (shielded). This equal many of themuch more expensive tone arm cable I tried from MSRP 500 to 4000.

I am itching to bulid a 5 meter XLR version of the bulk tonearm cable to serve as interconnect as it seems to have low capacitance. ANyone sees any problems with this concept.

Almarg- Oyaide is an interesting idea. PA 02 only has two connectors. Where does the ground goes in XLR, should I hook the ground to the shield?

What is the specifications in cap, ind, on PA 02?

Thanks

06-06-11: Glai
Oyaide is an interesting idea. PA 02 only has two connectors. Where does the ground goes in XLR, should I hook the ground to the shield?

Yes.

BTW, the Cable Company page for the PA-02 that I linked to earlier appears to have the description of a completely different cable, even though the title and photo at the top of the page are correct. Use the information at the Oyaide link I provided.

What is the specifications in cap, ind, on PA 02?

As indicated at the Oyaide site, the capacitance is 32pf/meter, which is very low.

Inductance is not directly indicated, but it can be calculated from the capacitance and the specified "characteristic impedance" of 120 ohms. Using the relation Z = square root(L/C), which is an approximation but an extremely close one in most relevant circumstances, the inductance works out to be 461 nanoHenries/meter, which is a reasonable number.

I'll add, though, that IMO inductance is an unimportant parameter for an analog interconnect. Under ordinary circumstances the impedance it represents at audible and even ultrasonic frequencies will be a completely negligible fraction of the input impedance of the component that is being driven, and therefore it will have no effect on the signal seen by that component.

Regards,
-- Al

So capacitance is the main parameter to consider for longer runs (where the lower the better)?

06-07-11: Madfloyd
So capacitance is the main parameter to consider for longer runs (where the lower the better)?

Capacitance and shielding, although the significance of shielding is lessened if the interface is balanced.

Shielding will affect susceptibility to both noise pickup caused by rfi/emi, and ground loop-induced hum and noise. The likelihood of both of those things becoming an issue increases if the cable length is long. Some cable designs achieve increased shielding effectiveness at the expense of increased capacitance, so there may be a tradeoff that has to be considered.

As far as lower capacitance being better is concerned, what matters (if you want neutral behavior, as opposed to a softened upper treble) is that the capacitance has to be low in relation to the output impedance (at high frequencies) of the component driving the cable. Reducing capacitance beyond that point would be overkill.

That can be calculated. Determine the capacitance C of the total length of cable, based on its specs. Calculate its capacitive reactance Xc (the capacitive form of impedance, measured in ohms) at 20kHz, based on the formula

Xc = 1/(2 x pi x F x C)

where Xc is capacitive reactance in ohms, pi = 3.14, F is frequency in Hertz, and C is the capacitance of the total length of cable in farads (1 farad = 1 trillion pf). As long as Xc is much higher (say 5 or 10 times or more) than the output impedance at high frequencies of the component driving the cable, you are good to go, as far as capacitance is concerned.

All of this applies, btw, just to line-level analog interconnects. Speaker cables, phono cables, digital cables, etc. are a different story altogether.

Regards,
-- Al