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| Phono cable and common mode noise filter? |
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| Richard Crowley:
--- Quote from: FriedMule on June 01, 2018, 03:57:07 am ---The changes did I make after this comment: ... To a start, I did not know if it would work so I asked here as my first question and got this answer: --- End quote --- Sorry, either I don't really understand what/why you are asking about this, or those other responses, while technically correct seem rather oblique to what I thought you were asking. --- Quote ---could you please explain it [impedance-balanced] more, maybe with a small schematic? --- End quote --- This shows RS which is the Source Impedance of the existing unbalanced output. Frequently there is actually a series resistor in the output path as shows, and that could be assumed to be the source impedance if you can't actually measure it. They simply create a "fake" ("impedance-balanced") "cold" output with the SAME output impedance as the active "hot" output. Then whatever noise is induced into the balanced path along the way will be picked up equally by the "hot" + side and thhe "cold" - side of the balanced audio connection. That gives maximum advantage to the differential input circuit at the destination end to reject the common-mode noise picked up by both the hot and cold sides of the balanced circuit. --- Quote ---I was trying to filter as you write, but got the answer that is was impossible, that I only could filter HF. --- End quote --- But 30KHz is exactly "HF", so your responses are very confusing. Do you REALLY mean 30 Kilohertz, or do you mean 30 Hertz? 30 KHz is almost trivial to filter out without even giving a second thought to balanced connections. While 30Hz is very definitely why we use balanced connections. |
| Richard Crowley:
And always remember that a "impedance balanced" output, and even a "real" balanced output by themselves do almost NOTHING to reduce pickup of noise and interference. It is the differential/balanced INPUT of the destination gear that does all the heavy lifting. This diagram shows the larger view and how the destination input circuit interacts with the source output circuit... https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcR-AtAyyBBuI_IN-ALsYLhM3vVGcaNNwEa13HoOVlq9QfPBgLY2 |
| Brumby:
With all the talk about the circuitry, I hope the cabling is not forgotten. To get the benefit of balanced line signal transfer, please make sure you use the proper balanced line cabling - the twisted pair inside a single shield. One cable per channel. Don't try doing this with two standard shielded cables - the sort you get in a set of stereo RCA leads - and just using the centre conductor of each as your differential lines with the two separate shields (connected however you like). If you have an electrically noisy environment and/or long runs, you will never get it to work properly. |
| FriedMule:
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. |
| IDEngineer:
--- Quote from: FriedMule on June 02, 2018, 03:59:10 pm ---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 --- Read this entire thread again, and consider these points: 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". 2) Your "standard of the shelf music sources" apparently do not have native differential outputs. The left channel, by itself, has no noise-free reference you can rely upon. So how would your magic filtering circuit "know" what is noise (to be removed) and what is signal (to be preserved)? That's what true differential signals do for you: Give you a way to distinguish between the signal and everything else. Here's a thought experiment: You are given a signal comprised of a square wave at 1KHz and a triangle wave at 1KHz and told to filter it to (using your words) a "clean signal". No other information is available. Describe what your circuit will do to "clean" this signal. You can't, because you don't have enough information. Is the square wave the signal and the triangle wave the noise? Is it the other way around? Now, consider your left (or your right) signal. Without a reference, how does your circuit "know" what to retain and what to reject? |
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