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Let me repeat that it's normal , so don't go chasing ghosts at the supply or input or wiring.
Op amps go stupid when fed way less than +/-15V , specially if both rails come down at a different rate, but it's not "broken" .
Same as seeing a car wavering right and left at a highway, and finding driver is drunk, stoned or has some cardiac or diabetes problem, don't waste time checking the steering system or loose wheels.
It can be tamed or killed by careful grounding/layout change ... which is not the case, we are repairing, nor redesigning.
That said, that "pfuiiiitttt" oscillation, as well as turn on/off pops and thumps is usually "swept under the rug" (which does not mean "solved" by any means) by some muting system
So go check that mute and if necessary replace or increase the time constant capacitor so it covers that noise.
Often mute circuits have an unsymmetrical RC time constant, by adding a diode, so it turns on slow (leaving plenty of time for amp to stabilize) but turns off fast, before the mouse fart is heard.
I'd check that area.
First by fixed muting with a piece of wire, so we check that mute can indeed stop it .
If so, we can tweak mute.
Not dissing anybody, just trying to save you some frustration or wasted time.
Op amps go stupid when fed way less than +/-15V , specially if both rails come down at a different rate, but it's not "broken" .
Same as seeing a car wavering right and left at a highway, and finding driver is drunk, stoned or has some cardiac or diabetes problem, don't waste time checking the steering system or loose wheels.
It can be tamed or killed by careful grounding/layout change ... which is not the case, we are repairing, nor redesigning.
That said, that "pfuiiiitttt" oscillation, as well as turn on/off pops and thumps is usually "swept under the rug" (which does not mean "solved" by any means) by some muting system
So go check that mute and if necessary replace or increase the time constant capacitor so it covers that noise.
Often mute circuits have an unsymmetrical RC time constant, by adding a diode, so it turns on slow (leaving plenty of time for amp to stabilize) but turns off fast, before the mouse fart is heard.
I'd check that area.
First by fixed muting with a piece of wire, so we check that mute can indeed stop it .
If so, we can tweak mute.
Not dissing anybody, just trying to save you some frustration or wasted time.
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