Long XLR's: PAD Venustas versus Mogami

I'll add to my previous post that a very experienced audiophile I know uses 30 feet of Oyaide PA-02 in a balanced configuration, with excellent results. It has much lower capacitance than the Mogami 2534. He has compared those two cables, and as might be expected the Mogami's presentation differed, in the direction of being more relaxed.

The Oyaide is about $28/meter in bulk (unterminated) form.

http://www.oyaide.com/e_audio/audio_products_files/pa-02.htm

http://thecableco.com/product.php?id=6451

Regards,
-- Al

What components are you connecting? If the connection is between your BAT Rex preamp and the power amp, and the existing cable is Mogami 2534 in a balanced quad configuration, the cable's capacitance is high enough to be causing a small but probably perceptible rolloff of the extreme upper treble, and a slight dulling of transient response, due to its interaction with the high output impedance the preamp has at high frequencies. See Stereophile's measurements.

I can't predict whether the PAD cable would be better, worse, or similar in that respect because its capacitance doesn't appear to be specified.

Unless the output impedance of the component driving the cable is low (and the Rex's is not low), I would not invest in a 40 foot cable without knowing what its capacitance per unit length is. And assuming you want the cable to behave in as neutral a manner as possible, and if it is the Rex that is driving the cable, you should try to select a cable having significantly lower capacitance than the Mogami 2534.

Finally, I would be cautious extrapolating from the experience of others if the component they are using to drive the long cable has significantly different output impedance characteristics.

Regards,
-- Al

Hi Floyd,

Driving the long cable from the PARC will make the output impedance of the preamp irrelevant. The only situation in which the output impedance of the component preceding the component driving the cable would matter (as far as that cable is concerned) would be if the component driving the cable were a passive preamp, or some other completely passive and unbuffered device.

I would characterize the Mogami's capacitance as being moderate, or perhaps a little on the low side of moderate. It is low enough to be negligible at more typical lengths, when driven by most components (including the Rex). One of its major strong points is its noise rejection performance.

Given the low output impedance of the PARC, I don't think that the sonic differences between the Mogami and other cables you may consider can be predicted based on technical factors.

Regards,
-- Al

Neil, one small correction to your reflective and interesting post. Anti-Cables (both the speaker cables and the interconnects) do not by any means have low inductance. In fact their inductance is considerably higher than that of most audiophile-oriented cables.

That would make their speaker cables, btw, not a good choice for use with electrostatic speakers such as yours, unless perhaps cable length is short or a slight upper treble rolloff is wanted. The cable's impedance rise in the upper treble region, resulting from that inductance, would (except for short lengths) become significant in relation to the very low impedance electrostatics usually have at high frequencies, attenuating the upper treble at least slightly. With dynamic speakers such as the Vandersteens that Stringreen uses, that would be a non-issue in typical setups.

Regards,
-- Al

06-03-11: Nsgarch
Al, my assumption (in the case of the AC's) is that the user keeps the two runs a reasonable (like 4" or more) distance apart.

Hi Neil,

That will reduce capacitance to extremely low levels, but will actually increase inductance from the already not particularly low value it has when the wires are twisted together.

See the numbers at the bottom of this page.

Best regards,
-- Al

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

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

06-07-11: Glai
According to the equation, I should be able to use cables of higher capacitance (Mogami) without audible roll off. In practise, the Mogami sounds quite rolled off. What other things do you think are at play there?

Don't know. I'd just put it in the category of cable effects that are technically unexplainable.

If you had an unbalanced interface, I would have speculated that perhaps the Mogami's excellent noise rejection capabilities might be introducing less low level background noise onto the signal than the cable(s) you are comparing to, at upper treble or lower ultrasonic frequencies. I've read a number of times that very low level high frequency noise can subjectively be perceived as increased "air" and ambience. But I doubt that that kind of effect would be at play in the case of a balanced interface.

Best regards,
-- Al