Audison Voce 5.1k disorted Signal

[Achim1409]

Hello, i have a Audison, on the Channels A ( A-Class) i have i disorted upper Sinewave, on the right channel its the lower sine wave. I expect a problem in the preamp board. It doesnt change, if i move any switch or HP switch. When the amp heats up, it becomes more. Maybe somebody had this failure allready. Also the Sub Channel is damaged, but i removed the Drive board for that channel, and the amp runs fine for a year. Maybe also somebody know something.

 

[Achim1409]

Find attached a nearly similar diagram.
OP Voltage is Ok. 28V DC, 14 +, 14-V

 

[Achim1409]

The problem appears only with a load connected. Then allready 0.1v input is enough. The the picture. That's magnified on the positive half.

 

[Achim1409]

If i increase or decrease the bias, the signal gets smooth. But i cannot believe, that each channel has the same problem with the bias. All are separated...