Noise - HK Sound House 600

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Hello, I have this PA system on the table. I'm working on hi-fi mostly this is first PA system.

ISSUE: There is huge noise on tweeter even if volume is down.

I'm trying to do something with power amp.
I added 22pF parallel to R27. but it not helps.

Do you have any idea what can be upgrade to do low noise ? Thank you for any ideas.

Schematics of poweramps: schematics.png
Service manual: hughes_kettner_lucas_600_service_manual.pdf
 

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