I'm trying to use my LapTop through my Hi-Fi.
Using the built-in soundcard I get a lot of digital noise superimposed on the audio signal.
I'm contemplating trying an external USB soundcard but, if the noise is on the 5VDC, surely the noise will still be present.
Anyone any ideas what to try ?
Using the built-in soundcard I get a lot of digital noise superimposed on the audio signal.
I'm contemplating trying an external USB soundcard but, if the noise is on the 5VDC, surely the noise will still be present.
Anyone any ideas what to try ?
A scope shot or something that shows the frequency spectrum of the noise would be a good start, if it is audible then how is it being created and from where...
Then how to define digital noise, as usual digital noise is of a higher frequency than we can hear....
That said a laptop is the worse possible source you could pick, design constraints (NOT JUST COST, BUT THERMAL ETC) make then noisy compared to a desktop PC. USB DAC would be better depending how good the USB supply is, and these can vary greatly in quality. Galvanic isolation is best......
Then how to define digital noise, as usual digital noise is of a higher frequency than we can hear....
That said a laptop is the worse possible source you could pick, design constraints (NOT JUST COST, BUT THERMAL ETC) make then noisy compared to a desktop PC. USB DAC would be better depending how good the USB supply is, and these can vary greatly in quality. Galvanic isolation is best......
Sounds like the culprit could be way more low tech faulty ground connection. Try changing the cable you use between the laptop and the HiFi system. Cures the problem in most cases.
And.....
I have pointed out some problems with using laptops as a source and the best method of solving the problem, some sort of galvanic isolation, where do DJs come into the equation!
Noisy club or venue is a bit different than sitting using a laptop at home, so is a bit irrelevant to your problem, but the perfect tool for a DJ.
I use a Dell M6500 (I7 core) with 12G of RAM and an ASUS cheepo with I3 core, the ASUS has less poser supply noise, its doing less work. The problem with laptops is trying to get the computing power people want in a confined space thus adding extra engineering problems to the equation and so there have to be trade offs, which can result in a nosier electronic environment (and generally does as well as less computing power when compared to a desk-top of the same specification, processor RAM etc).
I would be interested as I said in knowing what spectrum the noise is at, looking at the analogue supplies on the sound card would be a start, and could some filtering be added to reduce the noise. if you can hear the noise then there is a good chance there may be more you cant hear that is adding to the general RF pollution that is around these days.
I have pointed out some problems with using laptops as a source and the best method of solving the problem, some sort of galvanic isolation, where do DJs come into the equation!
Noisy club or venue is a bit different than sitting using a laptop at home, so is a bit irrelevant to your problem, but the perfect tool for a DJ.
I use a Dell M6500 (I7 core) with 12G of RAM and an ASUS cheepo with I3 core, the ASUS has less poser supply noise, its doing less work. The problem with laptops is trying to get the computing power people want in a confined space thus adding extra engineering problems to the equation and so there have to be trade offs, which can result in a nosier electronic environment (and generally does as well as less computing power when compared to a desk-top of the same specification, processor RAM etc).
I would be interested as I said in knowing what spectrum the noise is at, looking at the analogue supplies on the sound card would be a start, and could some filtering be added to reduce the noise. if you can hear the noise then there is a good chance there may be more you cant hear that is adding to the general RF pollution that is around these days.
Does the problem disappear when running on battery or when driving headphones? It commonly does.
It is not unusual for switch-mode power supplies to have rather strong capacitive coupling between secondary-side ground and primary AC/return or safety earth, due to the inevitable EMI filter caps. This seems to be particularly problematic in notebook power supplies for some reason, maybe because these often lack a safety earth connection. But even if they did have one, you would commonly still experience ground loop issues (some supplies use a 1k resistor between secondary-side ground and safety earth though).
An isolation xmfr usually helps, though its CMRR may struggle if one side is pulled to half mains voltage and the other to earth. Giving the offending leakage currents a path to earth and thus keeping both sides on about the same potential should help.
This sort of problem may also occur with an external soundcard as long as it's galvanically coupled to the host system (some use USB isolators) and has unbalanced outputs, with a purely unbalanced connection to the playback system. Balanced connections make life much easier here. In fact, it is quite easy to rig up an unbalanced output for balanced connection, you just have to know its output impedance and balance that out with a series resistor in the "cold" connection directly after the output.
It is not unusual for switch-mode power supplies to have rather strong capacitive coupling between secondary-side ground and primary AC/return or safety earth, due to the inevitable EMI filter caps. This seems to be particularly problematic in notebook power supplies for some reason, maybe because these often lack a safety earth connection. But even if they did have one, you would commonly still experience ground loop issues (some supplies use a 1k resistor between secondary-side ground and safety earth though).
An isolation xmfr usually helps, though its CMRR may struggle if one side is pulled to half mains voltage and the other to earth. Giving the offending leakage currents a path to earth and thus keeping both sides on about the same potential should help.
This sort of problem may also occur with an external soundcard as long as it's galvanically coupled to the host system (some use USB isolators) and has unbalanced outputs, with a purely unbalanced connection to the playback system. Balanced connections make life much easier here. In fact, it is quite easy to rig up an unbalanced output for balanced connection, you just have to know its output impedance and balance that out with a series resistor in the "cold" connection directly after the output.
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