Hi there,
I have just made a USB Sound card using a MAX4299 Stereo Amp and a PCM2900E Audio Codec. It didn't work properly at first, and whenever a sound was played a loud crackling sound would play, no matter what the actual output was supposed to be.
After spending ages error-checking and using an oscilloscope to work out where the problem was, I got the card to work perfectly but only if I connected the analog ground of the board to the ground of the oscilloscope. As soon as a I disconnected the oscilloscope ground, all I got was the loud noise again.
Does anyone have any idea why it would only work when attached to the oscilloscope ground, and if there is anything I can do to fix it?
Cheers
I have just made a USB Sound card using a MAX4299 Stereo Amp and a PCM2900E Audio Codec. It didn't work properly at first, and whenever a sound was played a loud crackling sound would play, no matter what the actual output was supposed to be.
After spending ages error-checking and using an oscilloscope to work out where the problem was, I got the card to work perfectly but only if I connected the analog ground of the board to the ground of the oscilloscope. As soon as a I disconnected the oscilloscope ground, all I got was the loud noise again.
Does anyone have any idea why it would only work when attached to the oscilloscope ground, and if there is anything I can do to fix it?
Cheers
You obviously have a grounding problem.
I take it you have amplified speakers. Are they by any chance grounded to the same ground as the scope? (I'll bet they are).
If so, I would immediately check the connector where they plug into the sound card, and the wiring to the speakers.
Wes
I take it you have amplified speakers. Are they by any chance grounded to the same ground as the scope? (I'll bet they are).
If so, I would immediately check the connector where they plug into the sound card, and the wiring to the speakers.
Wes
I presume you're using the +5v usb power for the board. Does the analog ground and power supply share the same ground wire? What happens if you use an external power supply?
For a different application i bought and used an isolated hub from these people.
http://www.bb-europe.com/
For a different application i bought and used an isolated hub from these people.
http://www.bb-europe.com/
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