DC Blocker - Suggestions?

Hi Ardbeg10,
By adding together the transformer sizes in the 555PS, Supercap, 2 x 135s, phono stage and turntable, plus a safety factor, I knew that it would need to be several kVA. The next step was to email Airlink Transformers, receive a delightful reply from the Engineering Director and discuss it with him over the phone. He recommended either a 3kVA or 5kVA model.

In order to allow for possible future expansion and to minimise impedance, I went for the larger model. The difference in cost between the two was negligible. The BPS5120MP also allowed me to step the output voltage down by 10V to a true nominal 230V (+/- the usual variation that occurs through the day), which reduces peak loads on the Naim power supply components by a few percent and knocks out transformer hum even further.

So in summary, I didn’t really calculate it. I went with the recommendation of the Engineering Director of Airlink Transformers. It seemed like a safe bet at the time!

Best regards, BF

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If it helps I went with the BPS2000 version (2KVA).

Another thumbs up for Airlink Transformers. Very good support and fine products.

I bought an Airlink transformer due to all the posts on a previous thread stating how good they are at reducing hum.
It made no difference to the hum I was experiencing so they appear to work for some issues but not for others.

If the hum is DC related then any true isolation transformer (galvanic isolation) will remove, it will typically be more a slight rasping sound and will vary in intensity throughout the day and may appear to come in ‘waves’ of hum with no load on the associated device.

If it’s of any help to the OP, the hum I was experiencing was not as Simon describes as mine was constant with no change throughout the day.

Hi Pedropete, then if it’s of help, I would suggest the hum you experiencing is possibly not DC related, and may simply be the construction tolerances associated with the transformer.
As an example my NAP250.2 hums more than my 552PS, NDX2, CDX2 which are all typically rather quiet.
When there is DC offset in the mains (my laser printer fuser heater seems to invite this in my house) then they will all buzz to varying degrees… so I can tell if something is printing and my music room, is no where near the laser printer :grinning:

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I’m curious in why Naim have chose not solving this as others have years ago? They use a different kind of transformer and if so, what is its benefits compared to what rest of the industry is using? As soon as I find a thread about humming amps it is 9/10 times a Naim amp…

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I think this has been discussed many many times. Naim choose high efficiency toroidal transformers which are sensitive to asymmetric mains /saturation because of SQ performance.
Additionally I understand they believe putting an inline DC remover mains side of the transformer impacts performance/SQ so don’t do it… like some other manufacturers do, but clearly this is a user option purchasing an inline dedicated commercial DC remover if wanted.
I think there was a run a few years back of some rather noisy transformers in their quiescent state that Naim used but they replaced anyone affected (they did with me).

To be honest I don’t see the problem… we see loads of pages of tweaks and elaborate chains for home network LANs and Wi-fi, but seemingly when it comes to Mains, then the enthusiasm for tweaks tends to dry up to some extent. There are several commercial DC blockers out there for the audiophile, and arguably they would be more beneficial than a particular home network Cisco Cat switch over another.

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I had a variable hum tone & volume that I diagnosed as DC offset, after some research I designed & made a DC blocking filter, & have to say, surprisingly, despite Naim’s advise to the contrary. it improved the SQ. And that has been the same experience with another forumite with a DC blocking filter.
Sad to say that although the DC blocking filter completely fixed the variable elements of the hum tone & volume, the hum remained albeit now at a steady unchanging level.
The main culprit was the CDX2 & its small transformer, so transformer size is not always part of the problem. The CDX2 was fixed with a ‘cuddly toy’ PSU, now only the power amp & tuner transformers have a soft hum.
I subsequently found the DC (asymmetric sine wave distortion) was from a nearby house on the same phase who’s owner is an artist who works in metal. He’s now set up in a workshop elsewhere, so no more variable hum tone, but the DC blocker is staying.

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Mike… indeed I am aware of your success, and in fact I am not personally surprised, DC on the mains and saturating a transformer Into clipping typically presents a very distorted duty cycle voltage to the rectifier… which can’t be a good thing in terms of producing low noise stabilised power supplies… so I would encourage Naim to think again, because although I don’t see it as an issue, clearly some do, at least have as a switchable option… it’s not too difficult to do… at least electronically… though when they fail it can be rather spectacular…

Yes it’s not the size of transformer, but it’s efficiency and minimum resistive (as opposed to impedance) components. Larger transformers tend to be more efficient than smaller, but not always.

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… & maybe think again (& a bit harder) about SMPS.

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100% agree - also it would be good if Naim were working on some quiet switch mode PSUs similiar to the ones Chord and Linn use as these maintain high quality sound without the accompanying buzz. The buzz was the main reason I gave up on Naim PSUs. I must confess some of the setup tweaks drove me to distraction, but that’s another thread,

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That’s because whenever someone suggests tweaking a mains issue the old-boys club slam them: it has to be a dedicated mains or nothing apparently. Of course, if Naim designed their expensive power supplies so they don’t need tweaking… or at least got over the “no filter/conditioning” mentality of the last century that would be good.

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There is a hint of sanity in the old-boys dedicated mains supply. In UK the power circuits are normally a “Ring Main”, this means a power ring looping around a numbers of sockets & returning back to its circuit breaker.
A separate single supply to a socket is a “Radial” circuit or that can be better as a dedicated radial off a separate supply independent of the main Consumer Unit (CB box).
However, per this thread subject, sine wave distortion such as causes DC Offset that emanates from the local supply, is not helped by a dedicated supply, unless that supply is via a balanced main transformer or a DCBlock Filter.

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I bought a Supra DC Blocker. Let’s see how this goes :slight_smile:

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Yes it will. I have a balanced mains transformer. The system is physically isolated from the mains via the gap between the windings. DC does not pass through to the system winding, so effectively, DC is blocked.

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Kind of, as the Mains is AC, and is coupled via a transformer, the output of the transformer is the mains.
Also transformers are typically galvanic isolators, that is they will only conduct AC and not constant DC…however unless the transformer is balanced it will still have asymmetric wave forms on its output, which will perpetuate ‘DC’ on the mains syndrome.
However one must take care of the mains earths between the output of the transformer (blancedj and the input, as there could be quite a potential between these, and if balanced should not be joined (unless you still want DC on your mains)

DC cannot pass thru a transformer winding

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and, by default, the two sides on the Airlink BLT ARE connected. Hence the DC offset still exists. Airlink told me this. You could cut the earth connection between both sides but I’m not 100% sure of the implications of doing so.

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Definitely - if you have perfect mains that’s great, but even though I have seperate consumer unit and dedicated supply for hifi some linear PSUs are very noisy. My solution was to opt for products with quiet SMPSs, but a good mains filter can improve LPSUs. As always nothing wrong with giving it a try if you have mains issues.