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Filter RF interference from mobile phones
Filter RF interference from mobile phones
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Old 2nd October 2008, 07:39 PM   #1
joydivision is offline joydivision  Portugal
diyAudio Member
Join Date: Feb 2007
Location: Algarve
Default Filter RF interference from mobile phones


So, I had to get myself a Vodafone Connect Pen (mobile broadband), as I'm studying and living there most of the time. The problem is: I am going to take one of my amps (the TDA clone), and a small pair of speakers, to have music, and the vodafone card, just like any GSM phone, is causing audible interference, that we all know so well...
In my LM3886 I don't have the problem.
So, I'd like to hear some hints on what can I do to filter that.
I am thinking of:

- putting a 330pF cap between -In and +In of the chipamps, and also the preamp section opamps.
- putting 10pF decoupling caps at +V and -V to gnd, at both chipamps, and maybe also the preamp opamps?
- "glueing" some aluminium foil at the insides of the case, that are free (unfortunately very few... as most electronic is mounted there), as the case is wooden...
- installing ferrite beads (those found, i.e, in usb cables) around the cables that go from chipamp output to speaker binding posts.
- I already have a simple LPF at the amp's inputs, in form of 100pF to GND. Should I add another cap to the input of the preamp section opamps, aswell?

Any further ideas?

P.S.: interference isn't coming from input wires:
I can pull them out, and regulate volume pot to 0%, and still hear the same mobile phone buzzes...
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