Help hunting down an odd fault

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Old Hand
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#1 Help hunting down an odd fault

Post by RhythMick »

I completed my brothers amp a while ago and have since made a number of improvements on the design. I took his amp back and applied the same improvements, but now have an odd fault that has me flummoxed.

The amp works fine by itself. We use powered subs. When I power on the left sub, no problem. When I power on the right sub the house circuit trips. I've confirmed the fault is within the amp (specifically the right channel) by swapping the subs over. The fault occurs when powering on whichever sub is connected to the right channel speakers.

I can post circuit diagrams and get into detail, but what has me flummoxed is that the speaker terminals have no connection to earth. The speakers are driven by output transformers. For my own amp I grounded the negative speaker terminal, but missed doing that on Geoffs. So the OPT secondary is entirely floating. I've examined the wires and there is no short, plus I've tested each speaker terminal and it has no connection to earth.

Any ideas how powering on an external sub connected to a floating OPT secondary could cause a trip ?
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#2 Re: Help hunting down an odd fault

Post by chris661 »

If the OPT is floating and the sub is grounded, you might find that there's some residual current to the sub's ground, which would trip the RCD.

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