Audio System X-Ion 280.2

Got this amp for repair. Everything working normal, but i have crackling noise on one channel.

1 RCA on left channel plugged, left channel nearly ok, right channel also playing noises, which belongs to the music.
Both rca cables plugged, more diaorted on both channel.

All filters of, if i press the button for hp or lp, and then deactivate a filter, for about a second everything plays normal.
I expect the TL072 at the input.
The op amp with 6 Volts is this circuit. Its nearly exact the same.
The other in the Preamp board have 30V.

So iam not sure if the voltage is correct, because this op amp is in the bias circuit.


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No, i cant see it on the scope. Signal trace i dont have. I use a small earphone speaker, but its not loud enough to hear that noise. I have 6.2V accros pin 4 and 8 on each channel.
It sounds, that the noise/music ist blending between the channels.. If i use only one rca input, i still have noise on the other channel. If i push lp filter on and off again, the other channel is quit. If i then connect the 2nd rca cable, the noise is again there. The same if only one rca cable is connected, push lp on and off, increase gain, the noise starts again..
I'd suggest buying a set of bluetooth headphones with a separate transmitter that has 1/8" or RCA inputs. You can sometimes find them for $20US here. They are worth the investment. They allow you to hear very quiet sounds/noises and allow you to pick the best grounding point, even if that point has voltage on it. You'd need to add a small, simple circuit to the input to protect them but it's only caps, diodes, resistors.

Have you tried this with both a standard head unit and with a ground isolated signal source to see if either made a difference?
You need to pick the closest ground. The ground plane near the test point is often best. You can also test across the two input pins of the op-amps when using an isolated tracer.

Start at the RCA input by placing the two tracer probes across the RCA shield and ground. The signal should be clean there.

Did you make the protective circuit for the signal tracer?
Yes, i build it like yours. Works very well. But in the preamp circuit, i cant here any disortion. Also when the ground from the tracer is connected to the rca shield, and i place positive at the positive speaker output. Only when speakers are connectedt to the terminal, then its starts disorting.
On the picture with the caps marked, I have clean, loud audio. Also on the tl074 left below. If I try the other op amps, the audio is very weak, and disappear,when I hear over the tracer. I use pin 4 for ground, and the op amp outputs for positive.


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I don't know if pin 4 (-15v) is a good choice. Find a good (close) secondary ground point). It may not make a difference but you'll definitely have a good reference.

If you haven't done so, read section 8 on the Beyond the Basics page.

The only op-amps that you'll have clean signal on are up to about where I marked on the diagram. Beyond U3B, you are in the feedback loop and may have almost anything (most won't look like clean audio) up until the output if the amp.
Ok, tried secondary center. ... All the same. I have good audio at the rca terminal. If i try op-amp in the bias circuit. Pin 1 and 2 are very loud, and disorted, Pin 5 and 6 and 7, are less loud, but also disorted...

IC U11 in the second picture, left lower one. I have the only with good signal, But this one is in front of the remote connector .