[dclaz]

Hi all,
 
I recently bought some Canare L-4E6S starquad cables for use with a pair of active studio monitors, however I've now read that starquad is potentially an inferior design for this application due to the increased capacitance. Is this likely to be a problem over small runs? The cables are 2m long. Theoretically, am I better off with twisted pair balanced cables?
 
Cheers

 

[Speedskater]

At 2 meters, a star-quad cable will not be a problem. Now if it were a 100 meter cable, the high total cable capacitance  could give some output stages problems.

 

[dclaz]

  At 2 meters, a star-quad cable will not be a problem. Now if it were a 100 meter cable, the high total cable capacitance  could give some output stages problems.

Cheers.
 
Out of curiosity, how exactly does the high capacitance affect things?

 

[yage]

  Cheers.
 
Out of curiosity, how exactly does the high capacitance affect things?

 
High capacitance will limit frequency response at the high end (treble).

 

[dclaz]

   
High capacitance will limit frequency response at the high end (treble).

I see. I've been looking now to understand the mechanism behind that.
 
According to this calculator, it really does not appear to be an issue for short cables... Assuming a 600ohm source impedance, 185 pF/m capacitance and a 2m cable, the cut off frequency where the signal loses 3dB is roughly 717kHz.... 
 
Is this realistic? I can't find a figure for the source impedance for the balanced outputs for my DAC, Xonar E1.

 

[yage]

The output impedance (used as the source impedance in the calculator) of your Xonar is probably an order of magnitude less than 600 ohms, so in the tens of ohms range. Cable capacitance is also probably an order of magnitude lower.

 

[Speedskater]

It's not a low-pass filter problem. (well in a few cases it could be)
The problem is that the output stage may not have enough horsepower to push current into a high capacitance load.

 

[dclaz]

  The output impedance (used as the source impedance in the calculator) of your Xonar is probably an order of magnitude less than 600 ohms, so in the tens of ohms range. Cable capacitance is also probably an order of magnitude lower.

I have no idea about the source impedence, but I thought that would be conservative. I checked the capacitance of the cable here: http://www.canare.com/ProductItemDisplay.aspx?productItemID=53
Is it the "Capacitance between twin Blue and twin White conductors" or the "Capacitance between conductors to shield." that we are interested in?

 

[yage]

  I have no idea about the source impedence, but I thought that would be conservative. I checked the capacitance of the cable here: http://www.canare.com/ProductItemDisplay.aspx?productItemID=53
Is it the "Capacitance between twin Blue and twin White conductors" or the "Capacitance between conductors to shield." that we are interested in?

 
Take a look at this page under 'shielded pairs'.
 
http://www.nationalwire.com/support_basicintro.asp#Capacitance
 
This makes it somewhat problematic as to how to interpret the electrical properties properly (say that five times fast!). A reasonable interpretation might be to simply add the two capacitances together, though I would email Canare to get the final answer.
 
Not knowing what Xonar version you have, I dug up an old Stereophile review of the Xonar Essence ST/STX (http://www.stereophile.com/content/asus-xonar-essence-ststx-soundcards-measurements) where they measured an output impedance of 99 ohms. Again, an email to Asus to get the actual number (if they have it) is probably your best bet.

 

[Speedskater]

As for how the cable capacitance  loads the output stage of the sending unit, it's the total wire to wire capacitance.  That's the unit length value  (pF per foot) times the total length.
From a noise pick-up prospective, each wire should have exactly the same capacitance to the shield as the other wire.  That's why it takes big expensive machines to make good balanced cable.  It's hard to make close tolerance cable.

 

[dclaz]

  As for how the cable capacitance  loads the output stage of the sending unit, it's the total wire to wire capacitance.  That's the unit length value  (pF per foot) times the total length.
From a noise pick-up prospective, each wire should have exactly the same capacitance to the shield as the other wire.  That's why it takes big expensive machines to make good balanced cable.  It's hard to make close tolerance cable.

Cheers.

 

[robrob]

  Hi all,
 
I recently bought some Canare L-4E6S starquad cables for use with a pair of active studio monitors, however I've now read that starquad is potentially an inferior design for this application due to the increased capacitance. Is this likely to be a problem over small runs? The cables are 2m long. Theoretically, am I better off with twisted pair balanced cables?
 
Cheers

 
Since the op is feeding active speakers I assume he's using single ended output probably through RCA connectors or TRS to send the signal to the active monitors. Since it's single ended there would be no common mode noise rejection from twisted pair balanced wire. So wouldn't a grounded shield cable like Canare Star Quad be better for RFI noise protection? I would think RFI noise would be much more of a concern compared to high frequency signal loss to capacitance because any RFI picked up will be amplified in the active monitors. The key here is the op really isn't discussing speaker wires because he's sending the signal to the speakers to be amplified remotely. We're really discussing an interconnect cable which would benefit from a shielded cable.
 
dclaz, I would use the Canare Star Quad cable to feed the active monitors. For single ended common ground use I'd use the two white wires for Left +, the two blue wires for Right +, and the cable shield for the common ground Left - and Right -. This will ground the shield and give you noise protection.
 
This is Canare Star Quad cable but the markings are for balanced line use: