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In the Forum: Audio Discussions
In the Thread: It’s mad, mad, mad... electricity.

Post Subject: PP3000 and 30KHzPosted by JOHNR on: 11/30/2015

Romy,
The common mode noise will lie between 5 meg and 8meg or 8 meg to 12 meg depending upon whether it is forward or backward mode working.
It does not have much to do with the 30Kilohertz.
It is possibly true that one unit may have filters to keep out such noise and that they work in both directions thus should also reject such emissions from a second unit. In real life, I doubt that - refer to the following text.

The regulatory system publishes a "mask" that a machine must comply with before being given an approval. The problem is that the mask is not adequate for high level audio. As an example powering a second dac whilst listening to music will affect the music and that in itself proves that they do interact.

The mains filters are basically inadequate.

If you are concerned that placing a 1uF cap across the mains spoils the sound then that surprises me because the cap by itself will alter the lagging power factor in a system by a miniscule amount. You should be able to add 100uF to bring the phase angle up to 95% lagging without altering the sound.
It looks to me as if your power factor is being corrected to a leading PF somewhere else in your system.

BUT, if your PP3000 unit operates with an internal power factor correction front end, the front end filtering will be minimal because the PF will be 95% or better at all times, but still lagging.

The least you should do at this stage is to try the "Y" network of 2 caps. These will sum the opposing voltages thus will self cancel. If this reduces the problem then the nature of the interference is essentially proven. The cap value is not in the audio passband therefore should not affect the audio.

A second suggestion is to fit a clamp on ferrite to the power cable on each unit. If no difference, then RFI is not your problem.

Question: are you by chance connecting each PP3000 to a single external ground rod?

John

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