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

Post Subject: Dual PP3000 unitsPosted by JOHNR on: 11/29/2015

This is classical common mode noise interference on a common supply. This type of noise will pass right through any power conversion technology and in both directions. Due to the timing variations, I would expect it to be a little bit of mains interference and a lot of cellular RFI.

Question -
Do these units have front end power factor correction? If they do not, then you need to search for products that do this.

I note from earlier posts that suggestions to fit dedicated filament supplies to tubes will help. I can help with that but you will have to wait a while.
One aspect of both small signal and large DHT tubes is that RFI can pass through the filament and be amplified by a factor of 1.

The supply should be a.c. only since it is the diodes that create the common mode noise. You can of course invest in a CMChoke on every tube if you wish starting with the high gain tubes.

I saw your post showing the hand drawn curly "snakes" through the main waveform but never saw any answers to curing what is a 5 meg RF waveform mixed in with the 60 Hertz. Cell traffic is peaky at certain time during the day explaining why it varies so much. If the interference is in fact RFI and not mains borne, it will give your sound the appearance of greater brightness and having a gritty characteristic.

Suggestions:
Suggest you try inserting a 5 amp rated common mode choke firstly on the Opera network. Look for a 3 to 5 milli-Henry choke

Fit a 1 uF/440 volt capacitor each side of this choke and see what happens. I use MKP1848 rated at 900 volts for this application.
If that works but needs more, add a pair of 33nF "X" type capacitors at the center of the filter; one on the 220 rail volt and the second on the 0 volt rail. Bring the legs together and connect to a ground point using thin, single conductor wire.

On the low power units e.g. DAC, install a 50uF oil filled motor run cap in series with the line side of the power feed to the DAC. This removes most broad band 5 to 8 meg of noise without spoiling the sound. This will help if you have lots of cellular traffic in the area. Does not require any ground path, it absorbs the RF.

Another question - what filtration does the PP3000 have on its output rails? As an example, does it have a common mode choke?

I saw you comment about manufacturers fitting too much filtration on their products. My experience is they fit only what Regulators such as TUV and the UL underwriters see fit. These standards are FAR TOO LOW for ultra fi.
John

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