DC on the mains
Subscribe to Ask Paul Ask a QuestionWhen AC mains get a dose of DC the connected audio equipment will hum. What can be done about this?
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When AC mains get a dose of DC the connected audio equipment will hum. What can be done about this?
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I got nuthin.
Got nothing
Signed in to PS Audio and YouTube… no joy.
Yea… I’m good now.
Apparently nothing can be done about DC on the mains 😉
It is not only the hum. What I have noticed is that the DC rail voltage can drop a bit (like 0.2 – 0.3V) and fluctuate a bit. Then if you have an amp with no feedback and DC-coupled at the output DC-offset can raise to like 100-150 mV which is not dangerous but just a bit annoying. That is my observation.
Paul,
I have a similar problem with hum in the transformer of my Esoteric integrated amplifier at our holiday flat. I already own a P20 power regenerator which I use on my hi-fi system at home. I had hoped that if I bought another PS Audio power regenerator for our holiday flat it would fix the hum problem. However, your comment at the end of your video indicated that it would just transfer the problem to the power regenerator – so I would still hear the hum. Would you please recommend a product which will solve this for me?
I agree Paul, beer has to be cold, the colder the better. I like Coors Light made there in Colorado, Miller 64, and Labatts Light, all low calorie beer to watch my weight.
Paul, you’ve raised some contentious subjects in recent videos, but I can’t believe you’re going to disrespect British beer. That’s really going too far! And it’s not warm; the Campaign for Real Ale (CAMRA) recommends 54°F to 57°F.
Apart from the problem with the beer, I still didn’t understand how the diode bridge removes DC.
Sorry about the beer remark. British beer used to be a joy because they were local beers served quite cold. Now they are, for the most part, big corporate beers – often cold, but not always. In any case, it’s been a few years since I visited a pub. Maybe it’s all changed. When I did go the big distributors had bought up all the independent pubs and made the owners carry only their lines of brews.
As to how the diode bridges work (two in series). A diode needs 0.6 volts to turn on and conduct. So, when you run the AC through a bridge, you love the first 0.6 volts because the diode isn’t yet conducting. Add two of those in series and now you’ve lost the first volt. If that first volt is DC, then the DC is blocked and cannot get through the bridge.
Hope that makes sense.
It must have been a few years ago, and yes everything has changed since 1980. There is much better range of varied and excellent beer sold these days, from a larger number of independent breweries, all served at an ideal temperature.
My first post on the video thread because I don’t have the patience for long videos!
I’m 100% with you on warm British beer. I hate it. Always have. I used to like a cold beer, usually Italian or Belgian, but a quality Belgian beer at room temperature is the pinnacle for me.
Having also lost some pounds, beer is out and gin is in (although gin was never out in the first place). Beer is full of sugar. You can drink as much gin as you like on a balanced diet and I’ve risen to the challenge.
Wine is OK in moderation, about 800 calories per bottle, so sharing a bottle with one or two people is fine.
Tonic was added to gin by the British in India as the quinine offered some protection against cholera and other diseases. It stuck. I’m sort of addicted to quinine, but have recently tried some tonics made without quinine. Takes a bit of getting used to, but you get more of the gin flavour.
Another alternative is using a VERY light cider as a gin mixer, like this one.
https://www.chapeldown.com/collections/cider
Toroidal transformers almost never use laminations in their cores. Instead the core is made of a ferrite material that’s typically suspended in an insulating epoxy matrix to minimize eddy currents. The hum experienced in the transformer is caused by the windings moving. I too had an issue with DC on the mains and used a home-built bridge/capacitor DC blocker and it worked great. Later versions of my amplifiers used fully potted toroid transformers which prevent audible humming without the need for the “blocker”.
I think it’s the capacitor that’s blocking the DC.
There is a big distributor in North London (actually in Borehamwood) called Futureshop. They supply DC blockers. They are a bricks and mortar business with a large warehouse (been there, it’s 10 minutes from me), not an internet reseller. George should give them a call. They will probably send him one on loan. I’ve bought cables from them and they are 100% good guys. They also sell PS Audio.