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| Need help with ground loop |
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| laejf:
--- Quote ---Screw that, try this. You said that external PSU for the BT makes it go away. So remove your 7805 and connect the external PSU to its GND and OUT pads. Should be quiet, right? --- End quote --- Yes, but the problem is that I don't want to add another voltage source i.e. another battery to it. So I'm looking for another way to perhaps get the USB-port floating with a single source. |
| laejf:
--- Quote from: DaJMasta on August 10, 2019, 07:20:28 am ---Differential mode could definitely do something, any picked up noise probably differential mode, but you want to keep the filter cutoff away from the audio band, since the input signal isn't differential. That being said, what about an RC or LC low pass filter on the audio inputs? Won't do anything to protect against like power supply noise, but would effectively eliminate high frequency noise picked up on the input cables. Shielded signal cables or shielding for the amp can be a viable option, too. Still, your best bet is going to be to scope it and see where it's coming from. With the gain options for the chip, you can probably still see noise on the inputs/power rails if it's significant on the output, so time-correlating them should show you where exactly it's coming from. Much more narrower scope (ha) of a problem to troubleshoot when you can identify where the noise is actually coming from. --- End quote --- Since the noise is hear-able, a low pass filter on the inputs would filter out music as well, wouldn't it? I will try to find out more with a scope, I'm not very confident in my skills in trouble shooting with scopes but I'll try! The class D amp also puts out a lot of noise at 250kHz which doesn't make it easier. Thank you |
| laejf:
--- Quote from: xlnx on August 10, 2019, 09:18:06 am ---I'd like to add that if the if the ground connection from the USB is your real problem, then you may use a digital isolator device from Analog Devices or Silicon Labs. Search for "USB 1500V" on eBay/AliX to se how it's done. That solution also has an isolated 5V to 5V power module with 1500V isolation to bring power to the isolated side - you may not need that if you can power it from the inside. --- End quote --- This is definitely something I'll keep in mind if I don't find a work around with what i have. Thanks! |
| magic:
--- Quote from: laejf on August 10, 2019, 10:58:40 am ---Yes, but the problem is that I don't want to add another voltage source i.e. another battery to it. So I'm looking for another way to perhaps get the USB-port floating with a single source. --- End quote --- The point is testing, finding out what's the source of the noise. I still suspect that ground return current is involved, although I'm not sure how to explain away lack of difference from reducing ground connection resistance other than maybe a few dB just wasn't enough for you to notice. Disconnecting the USB port from board ground and powering it with an isolated converter definitely seems like a solution. |
| laejf:
--- Quote from: magic on August 10, 2019, 12:01:54 pm --- --- Quote from: laejf on August 10, 2019, 10:58:40 am ---Yes, but the problem is that I don't want to add another voltage source i.e. another battery to it. So I'm looking for another way to perhaps get the USB-port floating with a single source. --- End quote --- The point is testing, finding out what's the source of the noise. I still suspect that ground return current is involved, although I'm not sure how to explain away lack of difference from reducing ground connection resistance other than maybe a few dB just wasn't enough for you to notice. Disconnecting the USB port from board ground and powering it with an isolated converter definitely seems like a solution. --- End quote --- I wrote in my original post that I tried powering the BT-module with an isolated source and that it solved the problem. Is that not the same or have I misunderstood your point? |
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