Electronics > Beginners
Phono cable and common mode noise filter?
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C:
You need to understand that when noise is added to a signal it is very hard to remove.
Music is generally thought of as 20hz to 20khz.

So 50hz & 60hz power is in the music band.
So if you already have some noise, you try to prevent adding more noise.

On some audio systems you find a large ground lug. This is to be connected to all parts of the system with large wires. The intent is to remove the differences between each part's ground.
For you CD this is the medal chassis.

Then for each stereo source you have a 3 or four wire connection.
With the ground bonding above the signal return should not be carrying much ground noise.
There still could be a difference in potential for the signal returns.
A differential input can work with this.
When you do use a differential input then you want each phono jack isolated.
Here your old amplifier might not use the differential inputs.

Think of each channel of a source as
Music source + noise1
Music return + noise2
at the output.
Noise1 is not the same as noise2. With out that ground bonding, noise2 changes.

The best you can easily do is not add more noise to the source output connections before it gets to your old amplifier's input connection..

Better connections is an important step.
You could twist the two pair output from the CD.
If the twisted pair picks up some common mode noise a differential receiver will remove it.

For shielded phono cables it is a different story. The shield is limiting the changes to center conductor while picking up noise.
This looks like a signal change to the differential input.
Here the best you can do is to have a low resistance AC connection to your OLD amplifier ground. But this is also adding more noise to your old amplifiers ground. That ground bonding is an attempt to reduce this.

If you filter out power supply noise, you are also removing music.
You fix this by not allowing power supply noise in.

Good cables and differential receiver connected to your old amplifier is two options.

C




JohnnyMalaria:

--- Quote from: FriedMule on June 02, 2018, 03:59:10 pm ---First I am wary sorry that I first reply now, but had some family busyness to help with.

I'll try to explain it better.:-)

The whole idea is to use standard of the shelf music sources that do not have balanced output. And then connect them to my amplifier. Unfortunately does my old amplifier get noise in what I think as the whole spectrum, 50hz and up.
So my thought was simply to take each channel's positive and negative leads, filter the common noise and thereby have a clean signal. When the signal is cleaned, I just want to amplify it.

--- End quote ---

So the noise you want to get rid of is neither created by the CD player nor picked up by the cables. It is generated by your amp.

Forgive the comparison, but it is like distilling tap water and using that to flush the toilet.
IDEngineer:

--- Quote ---1) If "my old amplifier get noise in what I think as the whole spectrum" means your amplifier is noisy, nothing you can do to its input signal will fix that. You can test this by shorting the inputs to the amplifier; does it still have what you consider excessive noise? If so, the source of the noise is within the amplifier itself and you can't fix that by manipulating the signals from "standard of the shelf music sources".
--- End quote ---


--- Quote ---So the noise you want to get rid of is neither created by the CD player nor picked up by the cables. It is generated by your amp.
--- End quote ---
Anyone else here starting to feel like this guy just needs to buy a better amplifier?  :horse:
FriedMule:

--- Quote from: IDEngineer on June 02, 2018, 06:58:23 pm ---Anyone else here starting to feel like this guy just needs to buy a better amplifier?  :horse:

--- End quote ---

LOL hmm yes that is what I have to do, or build one myself:-)
But it sounds like that it is not possible to filter out external common mode noise if there are only + and - wire on each channel? In a DIY amplifier.
C:

--- Quote from: FriedMule on June 02, 2018, 07:47:01 pm ---
--- Quote from: IDEngineer on June 02, 2018, 06:58:23 pm ---Anyone else here starting to feel like this guy just needs to buy a better amplifier?  :horse:

--- End quote ---

LOL hmm yes that is what I have to do, or build one myself:-)
But it sounds like that it is not possible to filter out external common mode noise if there are only + and - wire on each channel? In a DIY amplifier.

--- End quote ---

The problem here is that you have to have common mode noise to
to filter out

A single ended signal be it on a phono jack or BNC does not have common mode noise. Here you have signal + noise that is not common mode.
The center conductor caries signal + noise.
The shield caries return signal + noise.

The shield being exposed picks up environment noise.

No common mode noise here.

C
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