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Is the amp making the thumping sound when you are turning it off or is it making this sound while it is powered on? Can you be more specific?
Is the amp powering off or is the protection light coming on when it cuts out?
CHECK TURN-OFF thumps.
(lv rms output into 8 ohms)
A) Left channel ±2V peak.
B) Right channel ±2V peak.