Surround sound power supply RFI

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samsat

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I have a relatively old surround sound receiver/amplifier.
The power supply generates a lot of broad band RFI but I hear it mainly on VHF.
This happens even when the amp is in standby.
Unplug the amp from the mains and all noise goes away.

I could look at replacing the amp but would first like to take a look at seeing if I can sort out the issue.

Where would be a good place on the PS to start placing ferrite beads etc.

Thanks.
 

RFI-EMI-GUY

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Power cord to reduce the conducted signals, and where the amp feeds the speakers to reduce the radiated signals.

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samsat

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Thanks. I'll look at power cord options. In standby mode the actual amp is off so speakers are not active.
Interference level is the same weather the unit is powered on or in standby.
 

RFI-EMI-GUY

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Thanks. I'll look at power cord options. In standby mode the actual amp is off so speakers are not active.
Interference level is the same weather the unit is powered on or in standby.

When it comes to RF interference, nothing can be considered completely off unless you disconnect wires, the power supply could still be using those wires as a dipole.
 

nanZor

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You might want to plug into a Tripp-Lite Isobar surge-protector / noise filter. Not just the usual surge protector strips, but the ones that incorporate the isolated noise filters - hence the Isobar name...

They have vhf filters in them in addition to isolation and common-mode attenuation. My use is to help prevent some stuff around here from pumping their switching junk into the house wiring, where ferrites on the cords did little.

They've been out for decades, but these days they don't label the individual circuits, nor tell you that for the MOST attenuation, to use the outlet the furthest away from the AC cord input. They used to label them with 25/50/75/100 db attenuation depending on the model from just 1 to about 8 circuits and the attenuation added up in series.

I had one decades ago, and just got hooked on them again when they quieted down my own entertainment system.
 

prcguy

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I would think the noise would radiate more from the power cord vs the speaker leads as the noise would be generated within the power supply. For VHF suppression I've found three #43 mix large snap on ferrite chokes can reduce the noise considerably. You would place these on the power cord as close as possible to the unit. Doing the same to the speaker cables might also help.
 
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