Hello. I've been working on a couple headphone amp designs for weeks now. One is a design using a maxim max9722 headphone amp IC and the other is a slightly more complex build using NJM4556AD dual op amps. Both amplifiers share the same power delivery and charging system composed of a texas instruments BQ24072 li-po battery charger and STM6601 smart push button controller to handle soft on/off and low voltage protection. The 4556 based headphone amp also has a LTC3122 based DC/DC boost converter circuit configured to deliver +/- 12v to the 4556 op amp.
Both amplifiers are nearly silent almost no hiss or other odd noises I can attribute to the amplifiers themselves and I'm quite happy with the audio quality but I've been having persistent issues with RFI from my 4g cell phone when it's transmitting or receiving data within approximately 1 foot of either headphone amp.
I have read numerous guides on dealing with RFI and have implemented a number of suggestions. low pass filters on input and feedback circuits, ferrite beads, obsessive ground fill on both board layers. No matter what I try it doesn't seem to affect the signal bleeding in from the cell phone. I've held the amps right next to a number of other RF sources including routers, microwaves, AM/FM transmitters etc. and the only component that seems to introduce any noise at all is cell phones.
I've been a forum lurker for quite a while and I apologize for my first post being one asking for assistance but I'm kind of stumped currently on how to go about this problem and thought perhaps somebody with experience could give some suggestions.
Both amplifiers are nearly silent almost no hiss or other odd noises I can attribute to the amplifiers themselves and I'm quite happy with the audio quality but I've been having persistent issues with RFI from my 4g cell phone when it's transmitting or receiving data within approximately 1 foot of either headphone amp.
I have read numerous guides on dealing with RFI and have implemented a number of suggestions. low pass filters on input and feedback circuits, ferrite beads, obsessive ground fill on both board layers. No matter what I try it doesn't seem to affect the signal bleeding in from the cell phone. I've held the amps right next to a number of other RF sources including routers, microwaves, AM/FM transmitters etc. and the only component that seems to introduce any noise at all is cell phones.
I've been a forum lurker for quite a while and I apologize for my first post being one asking for assistance but I'm kind of stumped currently on how to go about this problem and thought perhaps somebody with experience could give some suggestions.