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I need to run a cable to my powered subwoofer, about 60 feet from my preamp. Both the sub amp and preamp have balanced connectors. Is there a good, and easy DIY yourself design for a 60 foot cable with balanced connectors on each end? I'd apprecieate any help.


Thanks.


Wes
 

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Wes -


I've been doing some research on balanced cables and I haven't had a whole lot of luck finding what I've been told is a true balanced cable.


You're probably asking what I mean by "true balanced cable." Here's what I've been told. Some systems have an active differential circuit that, for the circuit to work correctly, needs three conductors - Pos, Neg, and Neutral - in addition to the shielding. The circuit monitors the Neutral and adjusts the signal based on the feedback. The B&K equipment I'm purchasing has a Differential Balanced Circuit.


So far, I've only found one cable supplier, Audioquest, that has a 3 conductor balanced cable. I've found lots of options for a two conductor cable with XLR connectors. However, they use the shield as the neutral leg - which I've been told doesn't work as well.


Depending on your equipment - this may not even be an issue. If you find another, or other, supplier(s) that have a 3 conductor cable please let me know. I haven't purchased the Audioquest yet because they are expensive. However, I'm wondering if the old saying - "you get what you pay for" is true in this case.


Good luck.


Paul
 

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get some raw mic cable from a music store and some xlr connectors....


one can pick up belden 8412 for under a $1 per foot..... the connectors are only $3 to $4 each...


(a lower cost cable is standard pvc jacket 22 gauge 2 conductor with a shield..... a 100 ft section is less than $10)


the soldering is relatively easy.... pin 2 is hot, pin 3 is negative and pin one is the shield
 

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Also check any local pro audio / music shop for balanced XLR interconnect or patch cables. Examples here and here . You can get these in almost any length you need. You can use 'Mic' cable.


You can also buy bulk cable of this sort and the XLR connectors.


I have not seen a consumer powered sub with balanced inputs. What do you have?
 

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Quote:
Originally posted by tubeguy44
the soldering is relatively easy.... pin 2 is hot, pin 3 is negative and pin one is the shield
This is true most of the time for amps in the USA, but not always, I have several pro amps that are #3 hot. :)
 

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DrSpike69:


Studio subwoofers (e.g., Mackie) have XLR balanced in.


Ales
 

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Quote:
Originally posted by afilipi
DrSpike69:


Studio subwoofers (e.g., Mackie) have XLR balanced in.


Ales
Ah, I have seen, used, and own, pro audio powered subs (and speakers) with XLR inputs. :) I mentioned 'consumer' gear. I wasn't saying I have never seen a powered sub with XLR, just not 'consumer' subs. :D I was just wondering what sub was being used.
 

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Quote:
Some systems have an active differential circuit that, for the circuit to work correctly, needs three conductors - Pos, Neg, and Neutral - in addition to the shielding.
There is a + audio signal and an - audio signal, they are the same but opposite in phase. The sheild is at ground.....no neutral.



Quote:
The circuit monitors the Neutral and adjusts the signal based on the feedback
no, it doesn't.
 

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tvtech1 -


I'm not qualified enough to argue the point. I'm just repeating what I heard from B&K regarding the active differential circuit in their Ref. 50. You may want to check it out and see if you find the same thing. If you find out something different please let me know.


I'm planning on spending a lot of money on equipment, etc. to upgrade to separates that will allow me to compensate for the long XLR inter-connect cable runs (60-70 ft). I've been told it's better to run 60-70 ft. of interconnects vs. running the same length in speaker wire. I'm planning on putting the amplifiers for my rear speakers right next to them.


If the equipment doesn't monitor the signal through some means (i.e. netural), how does it know when and how much to adjust the signal strength (up to +/- 6 db)? This is supposed to be a feature of the B&K Ref. 50 and their Reference series amplifiers.
 

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DrSpike69 -


The new Velodyne DD series has XLR's. That's one of the reasons I'm considering buying the DD-15 (my cable run is going to be 60-70 ft) over the B&W ASW 850 (that matches my Nautilus 803 Speakers).


Paul
 

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Quote:
If the equipment doesn't monitor the signal through some means (i.e. netural),
There is no neutral.


There also isn't any reason for a special cable to allow the device to monitor the level, since the signal originates inside the device, it can sample it there.

Quote:
how does it know when and how much to adjust the signal strength (up to +/- 6 db)?
It doesn't know because it doesn't 'adjust' the level. It would be kind of dumb to have your amp arbitrarily adjust audio levels wouldn't it? Thats what the volume control does.


I think you're confused about balanced outputs. A balanced outputs is 6dB higher in voltage then an unbalanced output.
 

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tvtech1 -


After your responses I began to question my understanding of the issue. I called B&K and got clarification.


B&K does have an active differential circuit. As you stated, there is a positive, negative, and ground. The third conductor in the Audioquest cable is a ground, and being separate from the shield, supposedly rejects the noise better than if the shield is used as the ground.


As far as adusting the circuit, I was partially correct. When the cable is first plugged in - the circuit adjusts the signal output to compensate for the signal loss due to the length of the cable. To your point - It does not continuously adjust the signal.
 

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Quote:
the circuit adjusts the signal output to compensate for the signal loss due to the length of the cable.
How does it know how long the cable is?

Is the load impedance bridging or matching?

Why doesn't any other balanced equipment do this?
 

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Quote:
Originally posted by Paul D. K.
DrSpike69 -


The new Velodyne DD series has XLR's. That's one of the reasons I'm considering buying the DD-15 (my cable run is going to be 60-70 ft) over the B&W ASW 850 (that matches my Nautilus 803 Speakers).


Paul
Ah, cool. I have heard a little about this sub, it sounds like it would be very good. I'll have to check one out some time. Let me know if you get it how it works out for you.
 

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techtv1-


How does it know how long the cable is?


According to B&K - It doesn't know how long the cable is, but it adjusts the signal based on the impedence in the circuit which is in part based on the length of the cable as well as quality of the conductors, etc.


Is the load impedance bridging or matching?


Matching.


Why doesn't any other balanced equipment do this?


If the equipment has an active differential circuit - it does. Otherwise, they simply have balanced connectors.


B&K said if you have any other questions they would be happy to answer them for you - 1-800-543-5252 - Ask for Gerry or George.
 

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Quote:
Originally posted by Paul D. K.
techtv1-


How does it know how long the cable is?


According to B&K - It doesn't know how long the cable is, but it adjusts the signal based on the impedence in the circuit which is in part based on the length of the cable as well as quality of the conductors, etc.


Is the load impedance bridging or matching?


Matching.


Why doesn't any other balanced equipment do this?


If the equipment has an active differential circuit - it does. Otherwise, they simply have balanced connectors.


B&K said if you have any other questions they would be happy to answer them for you - 1-800-543-5252 - Ask for Gerry or George.
Not for anything but Professional audio has been using balanced XLR's since the ages of dino's (not that long ago but I can tell you it has been a very long time)


for balanced cable


you can run THREE seperate wires (14awg) each and still have a good noise floor. That is the advantage of balanced inputs. If the signal is not in both A+ AND A- it is getting cancelled out. Shielding can be used as ground as has been used for the past 20+ years in the pro audio world :)


edit: Taking this right from Crown's Amplifier application guide.

Quote:
from http://www.crownaudio.com/pdf/133472.pdf
Balanced Line

A cable with two conductors surrounded by a shield, in which each

conductor is at equal impedance to ground. With respect to ground,

the conductors are at equal potential but opposite polarity; the signal

flows through both conductors.
 

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Figgie -


I think I'm going to chalk this one up to "there's more than one way to skin a cat." I've done a lot of reading tonight on the subject and found that the cable construction quoted by you and techtv1 is the prevalent way to build balanced cables. I've copied below the section from Audioquest's Cable guide that discusses their approach to balanced cables. It's certainly different.


Quote: "When a double balanced cable is used with balanced electronics, it usually has XLR connectors on both ends. One conductor is used for each of the two positive signals, and the shield is used for ground. To us, this is a step backwards: the reference ground is just as sensitive to distortion mechanisms as the positive signals and so deserves exactly the same respect. For this reason (and for better performance when used with RCA plugs) all cables from Coral and above are triple balanced.


An XLR plug can make four possible connections. AQ triple balanced cables use the three pins or sockets to connect the reference ground and the inverting and non-inverting positive signals. The case of the XLR is used to connect the shield to chassis ground."


Maybe it's a gimmick, or just maybe, both ways work and one is better than the other. It appears, most people don't subscribe to the theory or know about Audioquest's version of a balanced cable. I don't know how to resolve the issue other than to try cables built in both manners and see if I hear a difference. Although it may be extremely hard, if not impossible, to find cables with the same conductor material etc. with the only difference being the way the XLR's are terminated.


This has been an interesting journey. Not sure where I'm going to end up. If a two conductor cable, terminated in the manner that's been documented/suggested in the numerous articles I've read, works as well as Audioquest's "triple balanced" solution, I can save a lot of money.


Thanks to you and techtv1 for your thought provoking feedback.


Paul
 
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