Preamp RFI problems

Jonnyc

Member
2004-10-20 4:30 am
I have built a 6 channel preamp using the following components:

1 HC11 Microcontroller
3 PGA2310 Volume controls
3 OPA134 Op-amps
2 Maxim Max4619 Analog Switch chips
Bunch of passive stuff.

The problem I am having is that when I plug the preamp into the wall (without any audio cables attached) my TV goes snowy when I turn on the preamp. It's obvious that the RFI is either going through the mains to the TV or it's being transferred through the air, which is unlikely (though still very possible) because my preamp is in an aluminum chassis.

I have three transformers in my amp ( they're not very good ones and not toroidal). One for the digital part of the amp, one for the analog +15V and one for the analog -15V. My analog and digital grounds are separate (except one point right by the PGA's as reccommended in the datasheet) and are floating. Earth ground is connected to the chassis.

While I realise that my grounding scheme is slightly less than safe, I'll fix that problem after I fix the RF problem.

What would be the easiest and cheapest way to start tackling this problem? What are all the different possiblities for what could be causing this interference?

Oh, and one more question... will adding toroidal transformers reduce the amount of popping in the speakers when I turn the power on the preamp off? Would I need them on both the digital and analog side? or just the analog side?

Thanks,
Jon