A little problem with Op-Amp

[badboy6120]

Hi everyone

do anybody knows a good Op-Amp that doesn't have any problems with wireless signal like Mobile???
When I put my cell phone on the case of my audio system and If someone calls me I hear the sound of cell phone' s signals on my sub ( I use the ap-amp as my sub's low pass filter)
I used 4558, TL062 and currently I'm using TL072 that is much better that those two.
Is there something better than TL072 ???

Thank U

[poynton]

1. - Don't place your phone on the system.

2. - Prevent RF from entering. Screen inputs, outputs inc. power

3. - if the opamp is only used as a low pass filter, either cripple the HF response by placing a small cap across the + and - inputs, and across the output to -input, or use an opamp with a lousy HF response eg uA741


.

[DF96]

Not an op-amp issue, but a circuit issue. Add RF filtering.

[Mooly]

Originally Posted by DF96

Not an op-amp issue, but a circuit issue. Add RF filtering.

Agreed... the reason the TLO72 appears better is probably because the 4558 is bipolar and the RF signal is being demodulated by the input transistors of the opamp. Almost like a crystal set radio.

Space between your phone and equipment is the best solution.

[badboy6120]

Thank you so much for your answers
but could you give me more info about this RF filters??

[indianajo]

Ferrous steel case for your circuit is good for RF filter.. Putting 20 turns of wire on a toroid core on the input power lines helps, too. Got rid of the florescent lamp interference on my disco mixer. It already had ceramic caps on the input lines to signal ground. Putting a 20 pf ceramic cap across the feedback resistor of your op amp, helps also.
If you have more money than junk power supplies, you can buy RF filters for AC power entry to a circuit from distributors. Corcom is one brand.