Balanced Jack Wiring

[David_NC]

I picked up a QSC CX-6 pro amp last week. This is an older model meant for installation I'd assume, as it has terminal strip inputs on the input board. There were various boards that slid into a slot on the back to provide crossovers, XLR and TRS inputs, etc. Mine has a blank panel, so that's easy enough to resolve - drill holes and mount the jacks.
My question is when I wire the jacks, do I twist the wires, run them side by side, etc? I'll have a signal + and - along with a ground. The jumpers will be maybe 6" long. Any suggestions are appreciated.

 

[swechsler]

I have several commercial amps like this. The manual should give instructions for wiring unbalanced signals. IIRC, you connect the center pin to +, and - and common together. Under no circumstances should you connect + and - together.

 

[swechsler]

OK, just reread your question, and it appears as if you're looking to wire in balanced jacks. Ideally you'd use shielded balanced cable, but you could probably get away with a twisted pair for each and then run a separate common if you don't have that sort of cable. If there is no potential difference between common and chassis ground then you can probably get away with no separate common at all.

Note that the reason I differentiate between common and ground is that with XLR connectors, they aren't necessarily the same. Again, the manual may give more info.

 

[David_NC]

OK, just reread your question, and it appears as if you're looking to wire in balanced jacks. Ideally you'd use shielded balanced cable, but you could probably get away with a twisted pair for each and then run a separate common if you don't have that sort of cable. If there is no potential difference between common and chassis ground then you can probably get away with no separate common at all.

Note that the reason I differentiate between common and ground is that with XLR connectors, they aren't necessarily the same. Again, the manual may give more info.

I'll have some Cat 5e cable I can use. I'd use a twisted pair for the + and - and separate ground to the jack's ground terminal, I take it (the ground is common between the two channels in this amp). I don't imagine the small gauge will make a lot of difference in this short distance. If it's too thin, I'll can twist something thicker.
I said terminal strips, as my other QSC has them along with jacks. This one actually has a Phoenix input connector, which is a bit more tedious to me, but I'm sure it's ideal in a permanent installation. Thanks!

 

[swechsler]

Due to the low current and short distance involved, the small gauge will be fine. The center wire in RCA patch cables is usually thinner than that.

Personally I find the binding posts tedious to use for line level signals. At least with Phoenix connectors you can make the connections in a more convenient spot and then plug them in.

 

[David_NC]

Due to the low current and short distance involved, the small gauge will be fine. The center wire in RCA patch cables is usually thinner than that.

Personally I find the binding posts tedious to use for line level signals. At least with Phoenix connectors you can make the connections in a more convenient spot and then plug them in.

Perfect, and thanks. I'll have to connect the wires to a 5 pin male header, similar to a USB motherboard header. I ordered a wire-wrap tool, which should be good with the Cat5e wire. Next, I'll swap out the terminal strip speaker connections for dual banana jacks. These changes will make the amp much more user-friendly for my application. I'll eventually use this bridged (900 watts into 4 ohms) when I finally get to build Tubezilla, a 15" driver in a 20" Sonotube.

Agreed about the Phoenix connectors. In a permanent installation scenario, they'd be perfect. One could prewire everything so that it's simply plug-n-play. Swapping out amps would be similarly easy.

 

[Semanon]

Do it right. Buy shielded twisted pair like a Belden 8451 or 9451 for short runs. It's like $0.40 a foot and is excellent.

If you want to use UTP cable, consider splitting the pairs to get any common mode rejection benefit (blue/white for +; white/blue for -, for example). But, while using multiple pairs will increase your effective conductive area to 21 AWG, it will reduce the effectiveness of UTP cable's best characteristics, noise and crosstalk rejection.

 

[David_NC]

Do it right. Buy shielded twisted pair like a Belden 8451 or 9451 for short runs. It's like $0.40 a foot and is excellent.

If you want to use UTP cable, consider splitting the pairs to get any common mode rejection benefit (blue/white for +; white/blue for -, for example). But, while using multiple pairs will increase your effective conductive area to 21 AWG, it will reduce the effectiveness of UTP cable's best characteristics, noise and crosstalk rejection.

My plan is to use a single pair of UTP for each channel with a separate single wire for the common ground. The wires will be less than 6” long.

 

[Catmanboo]

 

[whoaru99]

I picked up a QSC CX-6 pro amp last week. This is an older model meant for installation I'd assume, as it has terminal strip inputs on the input board. There were various boards that slid into a slot on the back to provide crossovers, XLR and TRS inputs, etc. Mine has a blank panel, so that's easy enough to resolve - drill holes and mount the jacks.
My question is when I wire the jacks, do I twist the wires, run them side by side, etc? I'll have a signal + and - along with a ground. The jumpers will be maybe 6" long. Any suggestions are appreciated.

Over that distance and more or less inside the amp I doubt it will make a difference either way.

That said, I'd twist the pairs because that's generally what you do with balanced lines so any noise is more commonly ingressed, which makes the balanced common mode noise rejection more effective. Again though, I can't imagine it making much more than a theoretical improvement in this situation.

 

[David_NC]

LOL depending on how neatly this turns out, I'll def do a pic or two. I'll get to try my hand with a wire-wrap tool, which should be fun.

Over that distance and more or less inside the amp I doubt it will make a difference either way.

That said, I'd twist the pairs because that's generally what you do with balanced lines so any noise is more commonly ingressed, which makes the balanced common mode noise rejection more effective. Again though, I can't imagine it making much more than a theoretical improvement in this situation.

Exactly. a couple twisted pair from a Cat5 cable should do it. The annoying thing is that I know I have at least 100' of it in various lengths, but I can't find any. I hate when I clean up and organize... stuff is so hard to find afterwards!