17-10-2016, 07:49 AM
As previously mentioned, measure the actual B+/- rails to see if they are sagging under high load.
I encountered many transistorised PA/Disco amplifiers during my time at Aitkens and one oddball fault which caused the symptoms you describe was the soft start circuit, usually encountered on big amps with toroid transformers but sometimes seen on small hifi gear too. The amp's would run quite happily through the startup resistors for quiet audio, but as soon as you cranked them up the rails would sag and the amp would hit protection mode. I can't see from the diagram but it doesn't appear to have a soft start, but you say this amp isn't the same as the one in the diagram?
Dave.
I encountered many transistorised PA/Disco amplifiers during my time at Aitkens and one oddball fault which caused the symptoms you describe was the soft start circuit, usually encountered on big amps with toroid transformers but sometimes seen on small hifi gear too. The amp's would run quite happily through the startup resistors for quiet audio, but as soon as you cranked them up the rails would sag and the amp would hit protection mode. I can't see from the diagram but it doesn't appear to have a soft start, but you say this amp isn't the same as the one in the diagram?
Dave.
