I have a NEC laptop which has an external power supply that causes serious interference to phone lines nearby. It has a high leakage current, touching the audio jack sockets hurts, as they are coupled by capacitors to 50% of mains. Any usb device attached to this is going to induce a lot of noise onto the ground.
Finally found the problem ! It was a very very tiny piece of copper from drilling the holes that bridges two circuit lines. Now the board is working.
Thanks again for the help.
Frank
Thanks again for the help.
Frank
Noise
Hi,
I'm using a Behringer UCA202 as a test injection device. I believe it is PCM2902 based. I'm posting here because UKRAM has noticed 1Khz spaced noise in the recorded spectrum. I'm getting this too. It's odd that the amplitude seems to be altered by the 'resampling quality' setting in the windows driver!
The test setup is very simple. Input and output are connected together. I play a 1 second sample tone and record it at the same time. I then do an FFT on the recorded signal.
I've tried 44.1KHz and 48Khz sample rates and the results are the same. The noise spikes are anything from -65dB to -85dB (of 16 bit fs).
Any ideas? Is this inherent in the chip/unit?
Hi,
I'm using a Behringer UCA202 as a test injection device. I believe it is PCM2902 based. I'm posting here because UKRAM has noticed 1Khz spaced noise in the recorded spectrum. I'm getting this too. It's odd that the amplitude seems to be altered by the 'resampling quality' setting in the windows driver!
The test setup is very simple. Input and output are connected together. I play a 1 second sample tone and record it at the same time. I then do an FFT on the recorded signal.
I've tried 44.1KHz and 48Khz sample rates and the results are the same. The noise spikes are anything from -65dB to -85dB (of 16 bit fs).
Any ideas? Is this inherent in the chip/unit?
PSU noie
I assume the 1ms periodic spacing of USB traffic is the culprit here, and that this is somehow getting in via the PSU. I don't think it's direct though because the appearance of these noise peaks is dependent on there being a test tone and they are arrayed either side with diminishing amplitude the further away they are. I assume it is some sort of mixing (modulation) effect.
Here's the resulting spectrum :
http://www.icemans.co.uk/uca202-1.jpg
I assume the 1ms periodic spacing of USB traffic is the culprit here, and that this is somehow getting in via the PSU. I don't think it's direct though because the appearance of these noise peaks is dependent on there being a test tone and they are arrayed either side with diminishing amplitude the further away they are. I assume it is some sort of mixing (modulation) effect.
Here's the resulting spectrum :
http://www.icemans.co.uk/uca202-1.jpg
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