Co-Ax and Soldering

[unbalancedgraham]

That is the wrong cable. You need a balanced cable. First though you need to know the input impedance of your preamp. If it is lower than the output impedance of the sound card, you are in trouble without an interface.

You need a two conductor cable and a shield.

On the RCA plug you connect black 3 and 1 which is the shield to the ground of the RCA plug. And pin two positive phase to the hot pin of the RCA plug. Now you wire the balanced connector normally,1 ground which is shield, pin 3 black, and pin 2 which is positive phase. You must do this to optimize signal to noise, and also have the signal correctly phased. Doing this wrong will lead to an out of phase condition.

But still you must pay attention to impedance first when attempting to float a line, which is what you have to do to do what you want. What I described above is a floating line.

Ahh ok, interesting because I usually use sommer miniature balanced cable for installation or hand leads. This would provide as much or adequate shielding if wired as you mention?

Also, my sound card does not state an impedance output but my preamp has an unbalanced input of 30ohms and balanced is 60ohms. So as it is servo balanced it would detect the signal as unbalanced and route to 30ohms.

I suspect the output of the sound card is around 30ohms but I can't be sure.

Thank you for the advice, all very helpful and interesting!

 

[TLS Guy]

Ahh ok, interesting because I usually use sommer miniature balanced cable for installation or hand leads. This would provide as much or adequate shielding if wired as you mention?

Also, my sound card does not state an impedance output but my preamp has an unbalanced input of 30ohms and balanced is 60ohms. So as it is servo balanced it would detect the signal as unbalanced and route to 30ohms.

I suspect the output of the sound card is around 30ohms but I can't be sure.

Thank you for the advice, all very helpful and interesting!

What is your preamp? Those numbers do not sound right.

The age of your preamp is important as older equipment had source and input impedances of 150 to 600 ohms, often 200 ohms in my experience.

Newer equipment has a source impedance of 50 to 60 ohms and designed to work into an input impedance of up to 10,000 ohms.

For digital balanced standard AES 3 the impedance should be 150 ohms in and out.

On the other hand unbalanced circuits have a source impedance of 1000 to 10,000 ohms. In my experience usually around 2000 ohms. These unbalanced outputs are designed to work with an input impedance of 50,000 ohms or close.

My bet is that your sound card has a source impedance of 2000 ohms and needs to see an input impedance of 50,000 ohms or thereabouts, or it will not be happy.

Now a lot of modern equipment has TRS connectors that can be balanced or unbalanced. If you use a mono plug then it is unbalanced and conforms to a spec. as I outlined above. If you use a stereo connector with tip and ring, then the unit sees it as balanced and conforms to the spec I outlined above.

However you can not float a line from an unbalanced source like your sound card into any balanced input, without a transformer or bridging IC circuit. Most often these days it is done with a bridging IC circuit.

You have been very sparse on the details of your equipment which makes it impossible to give you precise advice.

But my advice stands you can float from a balanced output to an unbalanced input, but floating from an unbalanced output to a balanced input creates no end of problems if you do not know what you are doing.

 

[unbalancedgraham]

What is your preamp? Those numbers do not sound right.

The age of your preamp is important as older equipment had source and input impedances of 150 to 600 ohms, often 200 ohms in my experience.

Newer equipment has a source impedance of 50 to 60 ohms and designed to work into an input impedance of up to 10,000 ohms.

For digital balanced standard AES 3 the impedance should be 150 ohms in and out.

On the other hand unbalanced circuits have a source impedance of 1000 to 10,000 ohms. In my experience usually around 2000 ohms. These unbalanced outputs are designed to work with an input impedance of 50,000 ohms or close.

My bet is that your sound card has a source impedance of 2000 ohms and needs to see an input impedance of 50,000 ohms or thereabouts, or it will not be happy.

Now a lot of modern equipment has TRS connectors that can be balanced or unbalanced. If you use a mono plug then it is unbalanced and conforms to a spec. as I outlined above. If you use a stereo connector with tip and ring, then the unit sees it as balanced and conforms to the spec I outlined above.

However you can not float a line from an unbalanced source like your sound card into any balanced input, without a transformer or bridging IC circuit. Most often these days it is done with a bridging IC circuit.

You have been very sparse on the details of your equipment which makes it impossible to give you precise advice.

But my advice stands you can float from a balanced output to an unbalanced input, but floating from an unbalanced output to a balanced input creates no end of problems if you do not know what you are doing.

Hey!

OK, so I'll come clean...! I have been reluctant to say my kit set up as I know it isn't audiophile grade at certain points - I've worked in pro audio so know a thing or two about studio gear and its performance and flexibility so have chosen (through situation) tyhis set up:

Lenovo Desktop->

-> Creative Omni 5.1 USB (unbalanced RCA and 3.5mm jack outputs) - No spec on their website as to the output impedance - >

-> Behringer MX882 Mixer / Line Driver (using to match the unbalanced signal with the balanced output I need to run to...) ->

-> Genelec 7050B Subwoofer (all 3 front channels + LFE run balanced in to this) ->

-> 3x Genelec 1029A Powered Monitor Speakers.

Now I know it may be a bit of a massive overkill to worry about cables with such a crappy sound card but, I am looking to upgrade in stages and for the prices of a few £ and my soldering I want to clear up as much noise as possible and make it future quality compatible when I decide (read - have the cash) to invest in a much better sound card at some point.

Hope you can let me know

 

[TLS Guy]

Hey!

OK, so I'll come clean...! I have been reluctant to say my kit set up as I know it isn't audiophile grade at certain points - I've worked in pro audio so know a thing or two about studio gear and its performance and flexibility so have chosen (through situation) tyhis set up:

Lenovo Desktop->

-> Creative Omni 5.1 USB (unbalanced RCA and 3.5mm jack outputs) - No spec on their website as to the output impedance - >

-> Behringer MX882 Mixer / Line Driver (using to match the unbalanced signal with the balanced output I need to run to...) ->

-> Genelec 7050B Subwoofer (all 3 front channels + LFE run balanced in to this) ->

-> 3x Genelec 1029A Powered Monitor Speakers.

Now I know it may be a bit of a massive overkill to worry about cables with such a crappy sound card but, I am looking to upgrade in stages and for the prices of a few £ and my soldering I want to clear up as much noise as possible and make it future quality compatible when I decide (read - have the cash) to invest in a much better sound card at some point.

Hope you can let me know

The simplest and your best connection is to just run RCA out from your sound card, to TRS mono jacks on channels 5 and 6 inputs. Use the mono TRS plugs, just tip and body, no ring. You can run the main outs to your Genelecs balanced.

The input impedance is 25 KHz which will be plenty for your sound card. You can buy those cables off the shelf for little money.

Using a floating line from your sound card will have no advantage.

The old maxim of "keep it simple stupid!" applies here.

I guess I should have made you list your equipment at the beginning and we would have saved a lot of trouble. Your Behringer unit does have unbalanced inputs, so use them.

 

[unbalancedgraham]

That is the wrong cable. You need a balanced cable. First though you need to know the input impedance of your preamp. If it is lower than the output impedance of the sound card, you are in trouble without an interface.

You need a two conductor cable and a shield.

On the RCA plug you connect black 3 and 1 which is the shield to the ground of the RCA plug. And pin two positive phase to the hot pin of the RCA plug. Now you wire the balanced connector normally,1 ground which is shield, pin 3 black, and pin 2 which is positive phase. You must do this to optimize signal to noise, and also have the signal correctly phased. Doing this wrong will lead to an out of phase condition.

But still you must pay attention to impedance first when attempting to float a line, which is what you have to do to do what you want. What I described above is a floating line.

Yes, apologies - I was a little bit shy of ridicule of the first stage of my set up and I muddied the waters as a consequence!

That's great advice, thanks!

Can I also ask which would be the best shielded cable you could recommend and can I wire up unbalanced to the xlr inputs using the same principal? I mean, would I wire the ground to just one pin as well as the signal?

Thanks again!

 

[markw]

Yes, apologies - I was a little bit shy of ridicule of the first stage of my set up and I muddied the waters as a consequence!

I don't know your experiences with other sites but we're not inclined to make fun of whatever equipment people have. Some here may be brutally honest when asked for advice though.

Anyhow, welcome to the machine. You'll get some good advice here. You lucked out and got the attention of one of the more knowledgeable members here.

 

[unbalancedgraham]

I don't know your experiences with other sites but we're not inclined to make fun of whatever equipment people have. Some here may be brutally honest when asked for advice though.

Anyhow, welcome to the machine. You'll get some good advice here. You lucked out and got the attention of one of the more knowledgeable members here.

Thank you for the welcome! Sorry, I have always been wary of forums but it's clear you guys are cool!

And yes, very thankful indeed!!

 

[TLS Guy]

Yes, apologies - I was a little bit shy of ridicule of the first stage of my set up and I muddied the waters as a consequence!

That's great advice, thanks!

Can I also ask which would be the best shielded cable you could recommend and can I wire up unbalanced to the xlr inputs using the same principal? I mean, would I wire the ground to just one pin as well as the signal?

Thanks again!

Buy a cable of the right length and termination from Blue Jeans cable, monoprice or an outfit like Sweetwater. These cables abound and cables of good and serviceable quality easy to obtain. I don't get hung up on wire!

I recommend that you use the simplest and easiest termination. You have an unbalanced source and your Behringer has unbalanced inputs. Use them. Don't make it complicated and float lines when you don't have to. You would only float the line FROM the sound card if you only had balanced inputs. There is no advantage whatever over using unbalanced to unbalanced. Floating just increases the odds of you making a mistake.

 

[unbalancedgraham]

Buy a cable of the right length and termination from Blue Jeans cable, monoprice or an outfit like Sweetwater. These cables abound and cables of good and serviceable quality easy to obtain. I don't get hung up on wire!

I recommend that you use the simplest and easiest termination. You have an unbalanced source and your Behringer has unbalanced inputs. Use them. Don't make it complicated and float lines when you don't have to. You would only float the line FROM the sound card if you only had balanced inputs. There is no advantage whatever over using unbalanced to unbalanced. Floating just increases the odds of you making a mistake.

Again, thanks for your time on this!

My only query now is that the four other channels on the behringer are xlr and they are I am using for my centre channel and LFE. So a floating line is my only option? Is this correct or am I being dippy?

I would buy a cable but I'm addicted to flux burn smoke

 

[TLS Guy]

Again, thanks for your time on this!

My only query now is that the four other channels on the behringer are xlr and they are I am using for my centre channel and LFE. So a floating line is my only option? Is this correct or am I being dippy?

I would buy a cable but I'm addicted to flux burn smoke

I think you only have two unbalanced connection on that unit.

You will have to float the other two. Remember that the black and ground connect at the sound card end. You wire the xlr normally. You are OK as far as impedance is concerned.

I have just realized you are in Europe, as you spelled center, centre.

 

[Speedskater]

If the receiving component has balanced inputs, even if the sending unit only has unbalanced outputs, there is a small advantage to using the balanced inputs. But the hassle of doing so often outweighs this small advantage.

 

[TLS Guy]

If the receiving component has balanced inputs, even if the sending unit only has unbalanced outputs, there is a small advantage to using the balanced inputs. But the hassle of doing so often outweighs this small advantage.

So small it is negligible and not worth the hassle.

People usually think hum is due to a defect of shielding, whereas it is almost always a ground loop issue.

Floating and balanced connections do absolutely nothing to mitigate ground loops.

The OP should be warned that desk PCs and internal sound cards are absolutely notorious for generating ground loops. However we will deal with that if the issue arises, which is likely given the nature of his hook up.