UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Rotel RX402 soft put-put

Mooly · 3rd Dec 2019, 9:01 am

Pleased to hear you found the cause of this.

Finding why it affects them is a whole different ball game, there could be a combination of both radiated energy involved (leads acting as aerials as you mentioned) and also having the energy superimposed on the household ground leads which will have significant impedance away from mains frequencies and so allow voltage to appear. If the audio set up has multiple ground connections (amp and source components individually earthed) then you have a second possible route for this stuff getting into the audio chain.

The energy would also likely couple quite well through the transformer primary/secondary barrier and again enter the equipment.

It would be interesting to put a scope on the SECONDARY side of the power supplies and see if anything was visible even though the amp in isolation is quiet.

3rd Dec 2019, 9:01 am	#10
Mooly Octode Join Date: May 2011 Location: Lancashire, UK. Posts: 1,351	Re: Rotel RX402 soft put-put Pleased to hear you found the cause of this. Finding why it affects them is a whole different ball game, there could be a combination of both radiated energy involved (leads acting as aerials as you mentioned) and also having the energy superimposed on the household ground leads which will have significant impedance away from mains frequencies and so allow voltage to appear. If the audio set up has multiple ground connections (amp and source components individually earthed) then you have a second possible route for this stuff getting into the audio chain. The energy would also likely couple quite well through the transformer primary/secondary barrier and again enter the equipment. It would be interesting to put a scope on the SECONDARY side of the power supplies and see if anything was visible even though the amp in isolation is quiet.