Noise in Amp from LED Strip & servo

Posted on Feb 4, 2014

TL072 is amplifying an audio signal which is going to speakers & arduino analog input. Amp is powered by a wall wart with 12V 2A output. The same 12V is also regulated to 5V and used to power an AVR. The AVR is being used to PWM, using a power transistor(TIP120), an LED strip taking 1A from the same 12V supply. There 1) Now the rapid switching of current for LED strip is messing up

Noise in Amp from LED Strip & servo
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the amplifier output. It`s working fine with LED Strip off but when using PWM, there is a high frequency noise in the amplifier output. I have a 0. 1uF and 10uF caps near power inputs for both AVR and amplifier. This is probably due to insufficient decoupling. Can someone please help me make it better 2) There is another independent source of noise I`m finding which I`m unable to explain. The audio is going into Arduino which is controlling a servo as well. As soon as the servo is connected, there is a constant loud noise in amplifier output. This remains even after powering the arduino and servo using seperate USB supply(only ground connected). I placed audio setup and servo data wire far apart since they may be interfering due to PWM used for servo, but it wasn`t of any use. Since in both cases, amplifier is producing noise, I think my amplifier diagram might be at fault. If I remove the amplifier, the audio stream reaches arduino without any noise. Anybody got any ideas how to remove these 2 noises Add a resistor on the non-inverting input of the opamp-something between 33K and 100K. Coupled with the innate input capacitance of the opamp, it should form a low-pass filter. See these in tube amps all the time-it`s called a "grid stopper, " and it helps prevent high frequency oscillation. and picking up radio stations. It shouldn`t effect the output much-a resistor in series with the input doesn`t change the signal voltage...

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