DIY Mains conditioning Power bar (Mains DC, and Mains voltage)

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I folks,

I'm not looking to open a can of worms on the supposed sonic advantages/disadvantages of mains conditioning.

Let me explain the situations: I moved to a new city in the last year, and since getting here every largish transformer I have hums. The toroid in my SS amp hums, an EL I'm using in a new amp hummed a bit when I tested it, I can hear the transformer in my Desktop computer hum, and the power amp for a home theater system hums, and there is now more background noise and a worse power off thump than there was before. These things are all in the same room, but the hum follows any of them around the house.

All of this humming is getting close to driving me insane. We also have a small aquarium pump elsewhere in the house that vibrates, so much so it has kept me awake some nights. I replaced one pump on warranty, thinking it was the pump, and then tried another brand, all of which were well regarded for being quite and smooth. Most of the time it is very quite, but sometimes it is extremely loud, I've noticed when it is being loud the Torioid in my SS amp hums worse. Both of them are loud right now in fact. CFL's seem to hum sometimes too.

My fiance hears the humming too, so I know I haven't just lost my mind. In fact, she though she was going crazy until she mentioned it and I told her I could hear it too.

So from some research I think that there is likely DC on the mains, quite a bit, or that there is some signal at higher than 60hz. Or both. Unfortunately I only have a DMM, so i'm not sure how to test for either of these. However, I'm going to be moving a lot over the next few years, so it occurred to me that I might as well just build something that deals with both.

I've found plenty of circuits for DC blockers, seems like some diodes and large capacitors in parallel is the way to go for that.

As for dealing with non-60hz signal that isn't into the RF range, I'm having trouble and looking for suggestions.

Additionally, the mains voltage is not very stable here, and rather high. Normal is 123, but I've seen it as high as 125 and as low as 118 when testing outlets. I've been getting more into vintage gear lately, so I was thinking I might want some a 117 or 115 outlets on my "power station". I may just buy a variac (which would probably hum too :headbash:), but what are some other solutions and ways of dealing with the unstable voltage, usually it will be go +/- 1v a few times a minute, with occasional big drops and spikes that aren't related to local draw.

Speaking of testing outlets, I've had to replace a few because of faulty grounds, I was thinking of incorporating some sort of fault detection circuit and indicator LEDs on my power station, any suggestions there as well?

I've got about 4x as many power bars as I actually need around here, so I have plenty of outlets, and appropriately rated switches and breakers to scavenge.

Sorry for the long rambly post- I didn't sleep well last night. Can you guess why?
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A reviewer for The Absolute Sound has the same problem in his home. He asked James Bongiorno, the designer of an amplifier under review, for help.

The only problem I experienced was occasional physical
humming of the large toroidal transformers in the amplifiers.
I’ve had this happen from time to time with other amplifiers,
so I know it’s something from the AC lines, not the
components themselves. In my location, it manifests itself as
a mechanical hum that swells and diminishes rhythmically at
what sounds like a 60-cycle frequency. It’s a sporadic problem in my
neighborhood, sometimes several days going by without
recurrence, and it fortunately rarely seems to happen while
I’m listening to music. This sound is entirely physical, i.e.,
you can hear it with everything turned off but the amplifiers,
and the speakers disconnected, and it is neither part of
nor does it affect the audio signal or circuitry.
I asked James Bongiorno if he’d explain the issue in greater detail.

James replied, "When this condition occurs, the blame lies squarely with
the power company, whose AC lines are dirty. Until power
companies literally clean up their acts, there are basically
three solutions. The first is to redesign the transformer so
that its flux density is much lower. Alas, the only way to do
this is to increase the overall size of the transformer, which
would affect everything else in the product, thus adding
substantially to the cost of everything including the shipping
carton and the freight. In my opinion, this ‘solution’ forces
the majority of consumers to ‘fund’ the very few with the

"A second solution, also expensive, is to find an original
PS Audio Power Plant, the one with the built-in regenerator.
I am under the impression that PS Audio’s current units do
not have this feature, which if true makes them of a no help.
Nor are any of the currently popular line conditioners and
filters useful in addressing the issue."

"The third solution is the most practical and cost effective:
the use of a little device called the ‘Humbuster,’ also originally
from PS Audio though no longer made. But it’s easy enough
to make one (or two for a pair of monoblocks) with parts from
Digikey, Mouser, or even a local RadioShack. It would consist
of a couple of 25-amp bridge-rectifier assemblies, a few
capacitors, and a small Bud box with an AC input and output

I managed to find a PS Audio Humbuster and can report
that once I plugged the amps into it, the problem never
recurred and the fine performance of the amp is otherwise
If you read Rod Elliott's article on Mains DC Blockers, you'll see that the circuit Rod recommends has the exact same parts list: a high-current bridge rectifier, a few capacitors, and a chassis & mains connectors.
Thanks all, I've read that article a couple of times and it is very good. I've decided that I'll put DC blockers at each device, as following his formulas I can get bipolar capacitors in the appropriate size and ratings for each device cheaper than 2 polar capacitors of twice the capacitance in series for a global solution as I was originally thinking.
We are talking about DC blocking of the mains feed to the transformer Primary.
The capacitance there must be enormous so that the impedance presented to the 50Hz is kept very low at normal transformer currents and low enough such that the diodes don't turn on when maximum power is being delivered to the speaker.
The capacitance requirement is complicated even more by the short duty cycle of the primary current. It mirrors the charging current in the secondary to rectifier circuit.

Expect C of 5mF to 10mF. I don't think 5mF bipolar electrolytics exist.
Though I could just parallel the same caps as a global solution I guess, so never mind. The effective ripple current rating of n identical caps in parallel would be (ripple rating)*n right? As for any given load and frequency the current would be divided equally. For different values you would have to account for capacitive reactance and other differences between them.
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High end amplifier manufacturer Bryston, includes a Mains DC Blocker as part of the internal circuitry inside their power amplifiers. They publish the schematics of many of their power amp products on their website.

I've snipped out the relevant part of the schematic of their 3B SST2 amplifier, and (crudely!) circled the Mains DC blocker. You can see the difference between what Rod Elliott's site suggests, and what Bryston ships in their commercial products.


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have you checked your consumer unit (fuse box) for 'work hardened' connections and loose screws? i had my consumer unit changed recently and almost all of my electrical problems have gone electrician said that everything was loose. i used to get bulbs blowing a lot and checked my consumer unit a few years ago and had to tighten everything up which helped but the new unit is much much better. might also be a good idea to check the ground/earth rod.
A reviewer for The Absolute Sound (which ask some questions to Mr. James Bongiorno, developer for SAE, SUMO and some other company) mentioned this:
This sound is entirely physical, i.e.,
you can hear it with everything turned off but the amplifiers,
and the speakers disconnected, and it is neither part of
nor does it affect the audio signal or circuitry
The last part of this statement is absolutely wrong - check out therefore the images in post #39 under
Variations of DC Main Filter against buzzing Toroid Transformers - what is the right?
In the second image one will note the huge current peaks due to saturation. If there is in use a torodial transformer without physical hum and audible noise, these current peaks can have a great affect to the power amp front end.
I. e., dc filter will enhance sonic quality in any cases, as long as DC on the mains and as long no dynamic loss occur due small capacities and too low DC voltages on the capacitors.
My approach was tested on a Pass Labs X250 - go to post 184 on page 19 under

For different circuit variations check out post #8.

and this thgread:
dc filter
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