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Making an unbalanced to balanced box
Old 30th January 2013
  #1
Here for the gear
 
🎧 5 years
Making an unbalanced to balanced box

First off, I'd like to say hello to everyone here at the forums. Seems like the best place to answer this quest to remove noise coming though speakers.

First of all, my chain starts at a stereo 1/8" out of my pc's motherboard > converter to two mono rca > left and right krk Rokit6's. I get a ton of noise from what sounds like the computer itself processing.

I figured if I would simply wire up a box to convert my 1/8" stereo signal into two mono TRS 1/4" cables to the balanced 1/4" input on my krks, I could fix the issue. I think I have the concept of a balanced cable down alight, but it was seeming a little to simple to create the box I had in my head. Here's what I planned to do:

1/8" stereo input > two TRS balanced 1/4" outputs. I would split the ground to go to both TRS outputs and then solder the left and right signals to both + and - leads of the TRS outs. Would this then create a balanced connection between the box and my monitors? It seems like it would not because how would the signal know which way to travel down the two leads? If I am wrong, what would the correct way to get a balanced connection to the speakers?

One last thing I had in my head. If I had a 50 ft unbalanced cable and then have some sort of conversion to balanced cables right before the output(say speakers), would all of the noise get cancelled out? Would it act like a filter I think it would?

Thanks for the read!
Old 30th January 2013
  #2
Registered User
 
Rick Sutton's Avatar
 
🎧 15 years
I can't tell you why you are having noise problems but I can tell you that your method for making a balanced cable is not going to work. Given the fact that you have two unbalanced lines to begin with you need to transform each one of those lines to a balanced connection. The two most common ways to accomplish this is:
1. Use a transformer for each line to balance it.
2. Construct or purchase an amplifier circuit to balance it.
You might want to check out some some system theory and IIRC the Rane company has a good tutorial on their site.
Old 30th January 2013
  #3
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savyurrecords's Avatar
 
🎧 10 years
This is why I hate the terms unbalanced versus balanced. It makes people think that unbalanced is all around bad. It is not it works just fine almost all of the time. The problem is when you run it a very long distance, and even then it might not be a problem.

Unbalanced will work just fine. The problem is your PC sound interface. You need a separate audio interface. Those sounds you can hear will never be filtered out through some wiring gizmo. You can get just about any one and your problem will disappear.
Old 31st January 2013
  #4
S21
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S21's Avatar
 
🎧 5 years
It is likely that you have a radiofrequency interference (RFI) problem and that the received interference is rectified in your powered speakers. One of the products is the noise you hear.

I take it that you are sure that the pc is the source - does the interference follow pc activity? Does the same problem occur with your monitor off?

If you have strong interference relative to a line-level (or headphone-level) signal then the interference is likely conducted along a metallic path between the source and the amp in your speakers.

That metallic path will either be your audio cables or (less likely) power cables.

Pay attention to grounding. If you have cut the ground pin on your pc, well that is probably the cause there. Signals will try and take the lowest impedance path to ground and if that is via your speakers, then so be it.
Old 31st January 2013
  #5
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Lotus 7's Avatar
To Mehnike,

There is not enough info in your original post to accurately determine the cause of your noise problem. It's possible that the audio card in your computer has a high noise floor and the noise you're hearing is actually part of the audio coming from the card.

It's also possible that the noise is being induced in your unbalanced cables and converting to fully balanced interconnects might help. As Rick said, your concept of converting from unbalanced to balanced is in error and to do that would take either a set of transformer or active converters such as those made by Rane, Radio Design Labs, Soniflex, ART and others. FYI: connecting the (+) and (-) inputs (together) on a balanced input will result in no signal at all.

It's also quite possible that as S21 believes, your active speakers are rectifying RFI and that's what you're hearing.

With the limited info provided, all of the above is pure speculation. As savyurrecords said, using an internal sound card is often prone to noise problems. Sometimes careful grounding may help, but more often going to an external interface which gets the analog audio circuitry out of the noisy digital computer environment is the easiest solution. A good external interface connected to your computer only via Firewire or USB will already have appropriate balanced outputs and will be a good match for your powered speaker's balanced inputs.

Sorry to not be of more help, but if I were facing your situation I'd first try the grounding the computer to a good power line ground and possibly try running an external ground wire between the computer and your speakers. However there should already be a very low impedance path there provided by the shield in your unbalanced cables. It's unlikely that may help very much, but it's worth a try. Properly converting your unbalanced stereo output to balanced is not worth the cost, and may not help at all. To do it properly will cost as much as just purchasing a decent stand-alone external interface, which is really the best way to proceed IMHO.

Start saving for a nice RME, Focusrite, MOTU, Apogee, or other "real" audio interface.
Old 31st January 2013
  #6
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by Lotus 7 ➑️
Start saving for a nice RME, Focusrite, MOTU, Apogee, or other "real" audio interface.
+1

computer sound cards are made with a few $$ worth of chips, prob 16 bit.

Get a real audio interface for a couple hundred $ if you really want to make music.
Old 1st February 2013
  #7
S21
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S21's Avatar
 
🎧 5 years
I agree that it is all speculation without more information.
Old 1st February 2013
  #8
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ears2thesky's Avatar
 
1 Review written
🎧 10 years
Ummm...this:

Whirlwind pcDI | Sweetwater.com

Duh.
Old 1st February 2013 | Show parent
  #9
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Lotus 7's Avatar
Quote:
Originally Posted by ears2thesky ➑️
As has already been pointed out, running an unbalanced connection may have nothing to do with the computer noise the OP is hearing, so changing to a balanced signal and/or interrupting the ground connection may not help at all.

The fixed insertion level drop of a Whirlwind pcDi is 20 dB (40dB with the switchable pad).

The output from an internal audio card 3.5 mm jack will already be on the low side (probably - 10dBv, at best) so requires most of the available gain on the OP's ROKIT 6's.

The pcDI is intended to drive low-Z, high-gain mic inputs, not active monitor line-level inputs. It includes high turns ratio step-down transformers.

IMHO subtracting another 20 dB from the signal is not likely to help his situation.

Whirlwind pcDI specification sheet:
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Making an unbalanced to balanced box-pcdi-specs.jpg  
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