# Audio amplifier coupling issue

I keep getting oscillation / uncontrollable noise with the following circuit. My input is a balanced audio signal which goes through a TL082 op amp configured as a differential amp. The output of the op amp feeds an STA540 power amp IC. What's frustrating is if I use either circuit independent of the other, I have no issues. I get a great, clean signal through headphones at the output of the op amp, and I get great, clean signal if I feed it directly into the STA540 and bypass the op amp. BTW - the balanced inputs arrive at the op amp decoupled. The output of the previous stage (not shown) already has decoupling capacitors.

I'm stumped. Any help is appreciated.

• You probably need a lot more decoupling on your Vcc rail in order to break the feedback that's occurring between the two stages. Feb 22, 2015 at 19:43
• I've gone as high as 2,940uF smoothing (between VCC and Ground) on VCC without any improvement. Is that what you mean? Feb 22, 2015 at 20:09
• Not exactly. You also need smaller ceramic capacitors, in the 0.1 to 10 uF range, mounted very close to each chip, to provide a low-impedance path for the higher frequencies. Feb 22, 2015 at 20:34
• Very close to each chip going VCC to GND, or VCC to the VCC pin on the chip? Feb 22, 2015 at 21:02
• Vcc to Gnd on each chip. Feb 22, 2015 at 21:20

You are using the TL082 out of specifications, $Input~voltage~range ~~\pm15V$, in your application is almost $17V$ also the power supply is very near to the maximum supply voltage, you should check the voltage on your capacitors.
Probably, the opamps are out or order and you should replace it, violating $V\tiny{ICR}$ is a bad idea.