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RF issue - insane noise from Logitech's Powerplay mat

phrosty

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Logitech's Powerplay mat is feeding a huge amount of noise into my PC through USB. My Scarlett Solo is affected heavily, making its XLR input basically unusable with a loud pulsing buzz that gets amped alongside the mic. A warning to any audiophiles! It seems I'm not the only one who's noticed.

I'd like to keep using the mat if possible -- is there anything I can do to isolate it? I've tried an ifi defender+ and it does nothing. Not sure what to do beyond that.
 

AnalogSteph

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Now if that doesn't help, then it gets interesting. The guy on Reddit tried some USB hubs to no avail, for example. It is certainly possible for RF to get into the mic input somehow (CMRR is never truly infinite), and a wireless charging mouse mat pretty much implies there's a lot of that floating around. I would experiment with the positions of both mat and interface / mic cable, if that makes a difference it is very likely to be an RF problem. If so, this may be worth bringing to the attention of Focusrite support as well.

If you find that the mic cable is involved, I might try one using starquad cable stock. This is used specifically where more resilience to external interference is required.
 

kipman725

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Hilariously I'm an expert in wireless power transfer. I would speculate that the mat coil(s) are been driven by a single ended driver which causes them to have an electric field that doesn't cancel. If one end of the coil goes + and the other goes - then the field a long way from the coil sums to 0. However if one end is kept at GND and the other end goes + and - we don't get cancellation. This causes common mode noise generation through capacitance to the environment. The other end of our common mode noise circuit is the USB cable. So we should attack the USB cable and wrap it round a load of ferrite cores to up the common mode impedance of our noise circuit. I don't know what frequency this is using but its going to be a few hundred kHz (hard to filter), 6.78MHz or 13.56MHz (easier). Try this core: https://www.we-online.com/catalog/en/WE-STAR-TEC#74271251
 
OP
P

phrosty

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Thanks for all the advice everyone, I really appreciate it.

It appears to be an RF issue -- I moved the mat to the other side of the room and plugged it into a USB charger, and the noise is still picked up by the Solo ~6 feet away. If I move the mat around mid-air then the volume of the noise changes.

I notice when I unplug the XLR cable from my Solo, the noise does go away (despite amping still increasing the audible noise floor of the interface) so I *hope* the cable is bad -- I'll make a new one and see if that helps things.
 

DonH56

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This seems like a good time to try a star-quad XLR cable...
 

Feyire

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kipman725

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gosh I hope it uses induction to transfer energy rather than capacitive coupling :O (would be tempting considering the form factor)
 

somebodyelse

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That gaming mouse must drain batteries fast if they offer a wireless charging solution. Too bad it doesn't come with a Faraday cage
140hrs even with all the LEDs on, which would be a pretty serious session. You can also charge it using a cable. I suppose a charging cradle and pogo pins would have been too simple...
 

Otnehs

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Hilariously I'm an expert in wireless power transfer. I would speculate that the mat coil(s) are been driven by a single ended driver which causes them to have an electric field that doesn't cancel. If one end of the coil goes + and the other goes - then the field a long way from the coil sums to 0. However if one end is kept at GND and the other end goes + and - we don't get cancellation. This causes common mode noise generation through capacitance to the environment. The other end of our common mode noise circuit is the USB cable. So we should attack the USB cable and wrap it round a load of ferrite cores to up the common mode impedance of our noise circuit. I don't know what frequency this is using but its going to be a few hundred kHz (hard to filter), 6.78MHz or 13.56MHz (easier). Try this core: https://www.we-online.com/catalog/en/WE-STAR-TEC#74271251

Based on this report, it looks like 6.78 MHz lines up. Do you still recommend the above core?


 

kipman725

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yep with 2-4 turns (if they will fit). You're looking to maximise the impedance at the frequency of operation.
 
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