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Home noisy cabling setup: can I improve it without changing the cables?

fabiospark

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Hello everybody,

in my home recording studio (my living room...) I have a "musik making" corner with a PC (an Intel NUC) and a Focusrite 18i20 interface.

I have a shielded 1+1 RCA cable that run from two balanced outputs of the interface to a Rotel ampli RCA input on the other corner of the room.
The wires of the two channels run side by side, as in the cheap RCA stereo cables we usually find in the box when we buy something audio related.

Like this (look only at the cable, not the connectors):
Scan 383.jpg

To go into the interface TRS outputs I'm using a pair of these:
Scan 384.jpg


This wiring has always been a little noisy but since I got the NUC, when I switch it on, a strong RF noise is added so I'm considering to
replace it with a balanced (differential) wiring, then putting a stereo balanced-to-unbalanced converter near the ampli.

Here's a question:

1 - Can I use the two cores and the two shields of one stereo RCA cable like the one above to make one channel balanced connection, with a TRS on one end and another TRS or an XLR to the other end? (It dipends from the converter input connector). Or that kind of structure, with the two shielded wires running side by side, would not be that efficient?

2 - Is there any alternative consideration I should do before taking the balanced + converter route?

3 - I have in house an RGB cable with three single shielded wires: could be of any utility?

I noticed that while the interface has the earthing wire in the power cord, the Rotel hasn't, so I thought that could be a grounding problem, forcing the shield of the audio cables
to work as grounding conductor too, to ground the Rotel through the interface so I tried to connect directly the Rotel to ground but the noise didn't change.

Here is the wirings:
Scan 385.jpg


Thanks.
fabio
 

Blumlein 88

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I hate giving advice about such from a distance. The RCA you show is probably not shielded at all. Switching to an RG59 or RG6 RCA cable with a good shield might do the trick (or might have no effect). Switching to the RGB cable is a good thing to try. It will be likely RG6. Just use two of the three that you need. If you already have the RGB cable, might as well try it and see as it is free. If that doesn't work you'll have to get another idea.
 
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fabiospark

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I hate giving advice about such from a distance. The RCA you show is probably not shielded at all. Switching to an RG59 or RG6 RCA cable with a good shield might do the trick (or might have no effect). Switching to the RGB cable is a good thing to try. It will be likely RG6. Just use two of the three that you need. If you already have the RGB cable, might as well try it and see as it is free. If that doesn't work you'll have to get another idea.
Thank you for your reply.

The two cores of the stereo RCA paired cable are shielded.

I tried with the RGB with TS jacks on the interface side and RCAs on the Rotel side and it better.
In the next days I will try to use the RGB also from the Rotel to the headphones ampli because I noticed that i'm gettin a bit of noise there too,
even when thr Rotel is off.

Would I get a better rejection if I use a double shielded cable? (Two shields around the two single core wires plus one shield around the two shielded cores?
In that case, maybe it would be better to connect the outer shield on one side only?

And what can you say about my question for using a stereo RCA cable (with parallel cores) to create a balanced connection?
Thanks.
 

Holmz

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My NUC was coupling in through the USB.
A sheild will not help that.
I needed to attached XLRs just to provide a nice ground between them, even though I was not using the XLRs for signals.

What is the nature of the noise, as in how does it sound?
Hiss, hum, or computer clicking?

If it is hum or clicking, then would be tying chassis grounds with the Rotel, Audio Interface, Media Box, PC and headphone amp as a first attempt.
I would think any screw on them would work.

This wiring has always been a little noisy but since I got the NUC, when I switch it on, a strong RF noise is added so I'm considering to
replace it with a balanced (differential) wiring, then putting a stereo balanced-to-unbalanced converter near the ampli.

The Jenson XRL to balanced transform is another solution that has elegance, and almost always works.

Adding the NUC and getting the problem, so of points to the NUC (IME).
 

antcollinet

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The twin screen+core will work as a balanced connector - but a proper balanced cable wil normally have twisted pair conductors - which gives additional noise immunity.

Most likely you'll get away with the cables you have.

Regarding your balanced to unbalanced connector - you probably want to avoid connecting the earth/sheld from the unbalanced side to the balanced if you can - and keep the unbalanced connections as short as possible: cm rather than m.
 

Holmz

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The twin screen+core will work as a balanced connector - but a proper balanced cable wil normally have twisted pair conductors - which gives additional noise immunity.

Most likely you'll get away with the cables you have

One would think so, but when I hooked up a USB to a DAC it was atrocious.
Finally adding some XLRs seemed to ground the DAC better.
But a USB isolator was another potential.


Regarding your balanced to unbalanced connector - you probably want to avoid connecting the earth/sheld from the unbalanced side to the balanced if you can - and keep the unbalanced connections as short as possible: cm rather than m.

The OP probably needs to try it with the shield connected to get a more solid ground connection.
Or at least me mindful that not connecting the shield at each end could be a problem.
They likely need to try it both ways, or be prepared to do that.

But if the noise is coming into the system as airborne, then that is different.

A grounding between chassis is an easy way to test things out. Prety much just need to touch it and listen to whether it is better or worse, or no effect.
 

Speedskater

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Yes you can use two coax cables to make one balanced interconnect.
Henry Ott (RIP) interference expert had a Power Point slide showing that.
Balanced_co-ax.jpg
 
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fabiospark

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"Twisted pairs or shielded twisted pairs are usually used in balanced circuits since a twisted pa is inherently a balanced configuration"

Does that mean that I could use a Cat 5 or 6 UTP cable to make an audio balanced connection?
 

antcollinet

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"Twisted pairs or shielded twisted pairs are usually used in balanced circuits since a twisted pa is inherently a balanced configuration"

Does that mean that I could use a Cat 5 or 6 UTP cable to make an audio balanced connection?

Probably - I've not tried it but can't see any reason it wouldn't work.
 

Speedskater

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Yes, the pros are sometimes using CAT cable for balanced interconnect systems. Some use unshielded and some use shielded. Its trickier for microphone cables.
 

Holmz

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"Twisted pairs or shielded twisted pairs are usually used in balanced circuits since a twisted pa is inherently a balanced configuration"

Does that mean that I could use a Cat 5 or 6 UTP cable to make an audio balanced connection?
Yeah.
 

Holmz

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"Twisted pairs or shielded twisted pairs are usually used in balanced circuits since a twisted pair is inherently a balanced configuration"

Does that mean that I could use a Cat 5 or 6 UTP cable to make an audio balanced connection?
^Yeah^.


But if the nature of the noise is a buzz computer sound, then it could be that the ground plane in the devices are not all the same.
(It don’t take much.)
and the twisted cable will not defeat that mechanism.

If it was a hum with the IC laying on top of a power cord with a magnetic field, then twisting is champion.

This:

... This wiring has always been a little noisy but since I got the NUC, when I switch it on, a strong RF noise is added
^this^ suggests it is the NUC, and some capture of the output, and analysis could show whether it is steady state noise, or some bursting and periodic spikes that are causing what sounds like RF noise.

so I'm considering to
replace it with a balanced (differential) wiring, then putting a stereo balanced-to-unbalanced converter near the ampli.
If it is the ground plane, then you need a better ground connection, so one side of the twisted pair, or another wire, needs to be a larger diameter.

You could use an isolator near the NUC usually a transformer of sorts, which are often RCA to XLR.

But ideally one should figure out the mechanism before determining the fix that mitigates, or ameliorates, the mechanism.
 
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fabiospark

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But ideally one should figure out the mechanism before determining the fix that mitigates, or ameliorates, the mechanism.
Yeah, that's why I've been looking for help.

Today I soldered 4 RCA at the ends of my half a skein of RGB left loosely coiled, and plugged them in to create a second way from the Rotel Zone 3 Out to the IN 3 of the Head Box. I thought that in this way I could check and compare the different noise picked up by the RCA cable to the RGB cable, at least from the Rotel to the Head Box.
At first I tried with the Rotel powered off, then with that on but with no input assigned to the zone outputs and in the end, with the "music making" interface input (RCA cable) assigned to both outputs and here's what I've got (look at the table to see all at a glance:

ScenarioNUCInterface
power
Cable A (12m)Rotel
power
Rotel input
to output
Cable B (6m)HP amp
power
Noise
name
Overall noise at normal listening level
1ononRCA stereo pair side by sideoffoffRCA stereo pair side by sideon1Very low level, almost nothing
4ononRCA stereo pair side by sideoffoffRGB (only R and B)on4Very low level, almost nothing
2ononRCA stereo pair side by sideonoffRCA stereo pair side by sideon2Medium level
5ononRCA stereo pair side by sideonoffRGB (only R and B)on5Very low level, almost nothing
3ononRCA stereo pair side by sideonmusic interf.RCA stereo pair side by sideon3High level
6ononRCA stereo pair side by sideonmusic interf.RGB (only R and B)on6Medium level

I highlighted the scenario 5 results because if you compare that with the previous one (num. 2) you can easily see that using the RGB cable between Rotel and Head box seems to make a lot of difference. I also put here the noises:
https://soundcloud.com/prik-m%2Fnoise-1%2Fs-g1unPXhQs0n
https://soundcloud.com/prik-m%2Fnoise-2%2Fs-DGodnGa3hcs
https://soundcloud.com/prik-m%2Fnoise-3%2Fs-m7kAJeCZs6e
https://soundcloud.com/prik-m%2Fnoise-5%2Fs-DNp9cUMhOVY
https://soundcloud.com/prik-m%2Fnoise-6%2Fs-4y7otu6r92D
 

Holmz

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Sounds like computer noises to me.

Is there a screw on the NUC case that you can attach a wire to?
 

antcollinet

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This is almost certainly ground loop noise - You don't describe how all the components in your system are grounded (or not)

But you don't even need any of them to be grounded - if your interface is connected to your PC with USB, you have a loop from PC through USB to interface, through RCA to Rotel Through RCA to HP Amp and back through RCA to PC. If you're not using USB you still have the loop via mains ground between PC and interface.

You also have multiple loops. There is another PC to HP amp to Rotal and back to mains vai rotel mains connector.

Those RCA Cables are long (12m and 6m), so I'm guessing the loop area is large - very prone to magnetic field pickup.

To elminate the noise, you need to find a way to break the loop, or use balanced analogue cables throughout. There is a reason balanced is used in professional applications.

How many of the analogue interconnects could you replace with optical?
 
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fabiospark

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This is almost certainly ground loop noise - You don't describe how all the components in your system are grounded (or not)
Yes, I did it, at least in part. In the drawing you can see that:
- the Focusrite (USB audio interface) is grounded trhough the power cord
- the Rotel is not grounded because the power cord and connector doesn't have the groung pin/wire
- the desk PC is a tower form factor with a PC 800W internal power supply that has ground pins and wire
- the NUC is powerred through a brickwall power supply so and I don't know whether it is grouded or not
- the Head Box is powered through an AC to AC power supply and I don't see no grounding pin nor wire.

To elminate the noise, you need to find a way to break the loop, or use balanced analogue cables throughout. There is a reason balanced is used in professional applications.
That's my original idea and not yet discarded, really. And than I would need at least one stereo converter.
How many of the analogue interconnects could you replace with optical?
None.

Thanks.
 
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fabiospark

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This afternoon I ran a new RGB cable from the interface (TRS BAl/UNBAL) to the Rotel STAGE input RCAs, and another one from the Rotel Zone 3 RCA outputs to the Head Box RCA input 1.
I soldered plugs with all metal body at both ends.
Then I made a little testing starting from scratch.
1 Switched off the NUC + Switched off the Rotel + cable RGB2 from Rotel Zone 3 out to Ch1 of Head Box = no noise (nothing else connected to the other channels of the Head box)
2 Switched Rotel ON with Stage input assigned to ZONE 3 out = nothing changed (no noise)
3 Switched NUC ON = RF noise started.
This is the main noise I would like to get rid of.

Should you need some other testing I'll be glad to do it.

Shouls I need to connect together the chassis of the NUC and the Rotel and/or of the Head box, in the RGB I ran the green is unused: can I use the shield of that?

I've been a professional electrician so no probs if you ask me to run wires or anything like that.

Thanks.
 
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