preenfm Forum

PreenFM => preenfm2 and preenfm3 => Topic started by: matrix12x on November 22, 2023, 01:10:34 AM

Title: filtering USB +5V line
Post by: matrix12x on November 22, 2023, 01:10:34 AM

Has anyone modded their Preen FM3 to add something like:

https://andybrown.me.uk/2015/07/24/usb-filtering/

Its a ferrite and some caps.

My PFM3 gets kind of noisy on USB power. Which I can work around with the DC connector and removing the USB DC jumpers. But, its just so darn convenient to use USB to power sometimes.

Title: Re: filtering USB +5V line
Post by: Toltekradiation on November 22, 2023, 07:54:47 AM

Hi,

i used ferrite on some diy modular, i think it's good to lower EMI noise a bit, but i don't think it would be enough to clean usb power, which can be very noisy..

There is also this kind of solution for this :
https://www.audiophonics.fr/en/interface-modules/usb-20-isolator-12mbps-1x-usb-a-to-4x-usb-a-module-p-17895.html (https://www.audiophonics.fr/en/interface-modules/usb-20-isolator-12mbps-1x-usb-a-to-4x-usb-a-module-p-17895.html)

i tried cheap chinese usb isolator, it was real junk,
the audiophonics may work, i have not tested it but it's a reliable website in my opinion.
There is other usb isolators around, but not cheap...

Title: Re: filtering USB +5V line
Post by: matrix12x on November 22, 2023, 07:59:48 PM

Thanks. I put one external ferrite on all of my USB cables, but that's generally just good for EMI/RFI. This is much lower freq than that since its in the audio range.

The circuit I showed above I can build super cheap and the ferrite is not the bolt around a cable type, it's the thruhole (or smt) type.

I was thinking of trying one if the audio isolators you linked to.

Title: Re: filtering USB +5V line
Post by: Toltekradiation on November 22, 2023, 08:07:47 PM

oh yes, i read your post a bit in hurry :-X

yes it's worth testing : just a few components :D

Title: Re: filtering USB +5V line
Post by: matrix12x on February 23, 2024, 10:31:59 PM

So while I had my PFM3 open for the booting issues I had, I decided to try out filtering the USB lines using the circuit from the link above.

it helps so much when operating from USB. The digital whine I would get when powering via USB is now inaudible. I'm very happy with this solution.

I probably should have measured the pre and post filter noise on my scope for completeness.

Of note, I was previously trying out a ferrite on the USB cable and it was not helpful for the USB induced noises I was hearing.

Title: Re: filtering USB +5V line
Post by: Xavier on February 25, 2024, 05:09:45 PM

Thanks for the update.
So here is the schema that fix the noise ?
Cool  :)

Title: Re: filtering USB +5V line
Post by: matrix12x on February 26, 2024, 12:22:29 AM

@Xavier  Exactly. Let me know if you want me to run before and after plots of the USB supply noise. I don't mind un-soldering and remeasuring.