DC Blocker in a power supply

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Greg
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#1 DC Blocker in a power supply

Post by Greg »

I have recently purchased for a nice price a 2KVA Airlinks Balanced Power Supply which is a basic model with no mains treatment apart from a spike suppressor. I am intending to add a DC blocker before the transformer, but have recently read elsewhere that DC blockers are in themselves filters that bring their own degregation to sound quality. I have no idea if this is true, so please can those who have knowledge on this express your observations on whether the addition of a DC blocker, whilst possibly stopping DC getting through might bring added degregation to sound performance. Certainly my own experience of filtering from when I built a 'Swampy' filter which others here tried was that it dulled and flattened the sound and rather knocked the life out of it.

At present my experience is that my new BPS has brought an improvement to sound in terms of speed and attack on notes, reveals more nuances and micro detail, bigger and better control to bass and a more realistic high treble, plus more transparency. Sounds good but read this in preportion. It's not night and day, but a pleasant and overall subtle improvement. Fitting a DC blocker seemed to me a fit and forget option that would deal with DC whether there on the mains at present or of it appears in the future. I know Ali and Gary have done this so all advice, knowledge and experiences on the value of a DC blocker are very welcome. In particular, does the inclusion in the mains supply effect the sound in any way?

Many thanks in anticipation.
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andrew Ivimey
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#2 Re: DC Blocker in a power supply

Post by andrew Ivimey »

I've heard more than a few of these devices because I have a friend who cares...( and has a considerable disposable income).

I like Swampy''s thingy. it's still in circuit upstairs with my 'ongaku' and it's a not bad system otherwise.

But from what I've heard with my friend who cares,who worries,there is a difference,which might be true. If the listener agrees the difference then one has to decide better or worse...

I don't bother and neither am I troubled with such devices.

Just how much money one has to spend and on what comes to mind in such situations.
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Ali Tait
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#3 Re: DC Blocker in a power supply

Post by Ali Tait »

In my case it was more about keeping the transformer quiet Greg, as toriods don't like DC.

Had to fit a 30A NTC too, as mine would trip the breaker on switch on. It is a 3kva though.
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#4 Re: DC Blocker in a power supply

Post by Neal »

I've used a DIY one for years on my PreII more out of curiosity than anything else and not noticed any downsides to sound quality. The short term power demands for your amp Greg are going to be supplied by the reservoir caps. I don't think a slight increase in impedance a blocker may or may not add to the mains supply is going to be an issue especially as the balanced tx is already adding it's own.
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#5 Re: DC Blocker in a power supply

Post by jack »

Ali Tait wrote:In my case it was more about keeping the transformer quiet Greg, as toriods don't like DC.

Had to fit a 30A NTC too, as mine would trip the breaker on switch on. It is a 3kva though.
Whilst the NTC is a good plan, the correct approach when driving inductive loads is to change the default domestic MCB on the ring from a "B" class device to a "C", and if it still trips at switch-on, to a " D"...
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#6 Re: DC Blocker in a power supply

Post by Ali Tait »

Yes, but didn't want to mess with the CU.
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Paul Barker
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#7 Re: DC Blocker in a power supply

Post by Paul Barker »

Out of interest, when altering household electrics.

Wife went to coroners hearing or whatever its call fe- father in law death. It transpires that a loose connection in a normal household socket in the bedroom, which mother in law (surviver beocause she was in hospital for broken hip) gave a statement on was always noisy. Anyway said loose connection gave off sufficient carbon monoxide while it burned away. Because we all know arking is a hot temperature and able to burn any combustibles near bye. Enough CO that is to cause death of father in law who was found dead far end of bungallow from the source almost at the back door. He din't quite make it. After which, through the night the flames eventually took hold and the place was burned down.

Respect any arcing noises you get when you walk past an accessory or a socket or plug something into it. S8crews come loose due to the 50hz and need tightening when that happens. This is why quite a long time ago, I think it was with 16th addition, that the use of joint boxes where they were inaccessible was banned. Best practice is one continuous cable from accessible point to accessible point, which should allert the user to get something done about strange noises.

I had never been in their bedroom, and being old people they managed their situation within their own minds without telling anyone.
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#8 Re: DC Blocker in a power supply

Post by jack »

Was really sorry to hear what happened Paul - I completely concur with "noticing the little things", like noise from fittings... or a wall being warm...

We have a small cottage we rent out - only rebuilt about 10 years ago with all the right paperwork.

During a check last year, the tenants mentioned that one of the ceiling lights in the sitting room had been buzzing & flickering a month or so back and about two days later the rest of the ceiling lights stopped working - I asked them why they hadn't mentioned it before, to which they replied that they knew the inspection was coming up and would mention it then...

The MCB hadn't tripped and the smoke detectors hadn't sounded. When I removed the fitting the top had completely melted/burnt out - a right mess of molten plastic etc. - Arcing had started due to a screw not being tight enough, eventually it carbon-tracked and the unit burnt out in the ceiling - that fitting was the first in the chain of 50W halogen down-lights, so was carrying the most current...

Thankfully, there was a fire hood over the fitting (as is required in the regs) and the void was filled with insulation (rock wool), so the fire didn't spread...

Why oh why didn't they report it when they first heard it buzzing? It could have been disastrous if the fire hood hadn't been there - who knows what could have happened. Naturally we also have sealed C0 & smoke detectors - sealed so the tenants can't remove the batteries to have a cheeky smoke, though I have seen them put plastic bags over the detectors in the past - we now explicitly mention in the contract that tampering with or deactivating any safety item, i.e. the detectors, is absolutely not allowed.

Remember this is a fairly new building to modern regs with up-to-date certification and but for pure luck (and the modern regs) it could easily have burnt down & killed or seriously injured the occupants. All now replaced with GU10 LEDs...

I won't even mention my in-laws' farm. Nightmare territory.
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Paul Barker
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#9 Re: DC Blocker in a power supply

Post by Paul Barker »

wellweareletdown by manufacturers.

i was full scope and have had many such light fittings do likewise. they are apauling quality.

any screwed joint can and many will come loose due to the 50hz oscilation, inspight of correct torque on installation. The hazard is one of the things checked and corrected in a PIR which is recommended 5 yearly but not required in law.

This is decided as a result of deaths from such causes.But fil situation is as rare as hens teeth, so shant result in a change.

Gas explosions are much more prevelent hence the laws over gas inspections for landlords.

I choose to work in these realms where I stand on the front line of ptotecting public. But I'm paid £1 more than a shelf stacker.
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#10 Re: DC Blocker in a power supply

Post by jack »

Completely concur on the quality of fittings issue - we didn't skimp on fittings and all are from (allegedly) reputable manufacturers via long-established factors.

Just read up about PIRs - it said that as a landlord I should have one done every 5 years - I'll sort one out ASAP...

Ta
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rowuk
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#11 Re: DC Blocker in a power supply

Post by rowuk »

I would think that the DC blocker is the second best solution. The first would be to get the DC out of the line so that we wouldn't have to filter it later. Maybe a dedicated power line for the stereo and no power supplies/house appliances that radiate junk?

Maybe we need some 1:1 isolation transformers with a gap?
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Paul Barker
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#12 Re: DC Blocker in a power supply

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rowuk wrote:I would think that the DC blocker is the second best solution. The first would be to get the DC out of the line so that we wouldn't have to filter it later. Maybe a dedicated power line for the stereo and no power supplies/house appliances that radiate junk?

Maybe we need some 1:1 isolation transformers with a gap?
Ideal, but costly if your hifi has a lot of demand. Just the laminations for say a 1kva one with air gap would probably weigh in at between £50 and £100. When I made a 3kva one for my 3 phase milling machine Laminations alone cost me £100 and it was standard assembly, interleaved because I didn't gap it. copper was near enough another £100.

For a gapped core of minimal noise you'd be talking same sized beast just for 1kva.

But if you wanted just to make specific gapped power tramsformers for the duties in the hifi chain that mattered, it would be a lot cheaper. You would make the particular power transformer for the specific seperate gapped. It would probably come out twice the size and cost of the equivalent interleaved.
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Paul Barker
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#13 Re: DC Blocker in a power supply

Post by Paul Barker »

Paul Barker wrote:
rowuk wrote:I would think that the DC blocker is the second best solution. The first would be to get the DC out of the line so that we wouldn't have to filter it later. Maybe a dedicated power line for the stereo and no power supplies/house appliances that radiate junk?

Maybe we need some 1:1 isolation transformers with a gap?
Ideal, but costly if your hifi has a lot of demand. Just the laminations for say a 1kva one with air gap would probably weigh in at between £50 and £100. When I made a 3kva one for my 3 phase milling machine Laminations alone cost me £100 and it was standard assembly, interleaved because I didn't gap it. copper was near enough another £100.

For a gapped core of minimal noise you'd be talking same sized beast.

But if you wanted just to make specific gapped power tramsformers for the duties in the hifi chain that mattered, it would be a lot cheaper. You would make the particular power transformer for the specific seperate gapped. It would probably come out twice the size and cost of the equivalent interleaved.
Of course if you want it balanced, which you may aswell for a complete job, add more money to your project fund.
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#14 Re: DC Blocker in a power supply

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Paul Barker wrote: any screwed joint can and many will come loose due to the 50hz oscilation, inspight of correct torque on installation. The hazard is one of the things checked and corrected in a PIR which is recommended 5 yearly but not required in law.
This has just reminded me, the old bungalow had an electric immersion heater, with a switch on the wall, (but not the only means of switching it mind as there was also a timer for economy 7). This switch and the associated wiring in and out was always "uncomfortably warm" when on, bearing in mind 3kW going through it.

As the switch wasn't actually needed to switch anything, I sort of converted it to a junction box as it were by removing the wires from the screw terminals and soldering them directly together. After that the fitting and cabling always remained stone cold. Just goes to show!
 
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#15 Re: DC Blocker in a power supply

Post by Paul Barker »

A common experience. Also happens with showers.
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