Why does noise floor drop when you add a large psu?

On the face of it, one might expect there to be more noise in the system with bigger external power supplies.

Is it mainly about the quality of the supply, and how the electricity is generated?

That’s the million dollar question, seems generally you don’t get the “best” out of most Naim products until you add an external power supply. Not being very technically minded I struggle to see why it makes such a difference, but it clearly does.

I must admit i scratch my head on this one. If you look at the nd555 internals there is a digital powered side and an analogue side…does not look that power hungry to someone like me. So powering both with what looks to be a massive overkill psu the 555 dr doing both sides brings a really good result. But add another so the analogue and digital have their own 555dr brings a nice uplift…i don’t really understand why one psu is not enough. The 555 dr psu have transformer and capacitors that muscle amps would be proud of?

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Let’s not forget the following:

  • The more expensive transformers have better regulated outputs. Even when both are DR, the larger ones provide better smoothing capacitors.
  • A large torodial core respective to the current draw is less likely to come anywhere close to flux saturation, thereby making for less EMI noise from the transformer.
  • A big issue for toroids is their somewhat Jeckel and Hyde nature. All things being equal, with stable mains, they deliver current without much if any EMI from the core. Compared to EI transformers that still generate EMI under good conditions and need some type of sheilding between them and sensitive components. But EI are fairly tollerent to less than perfect mains and things like DC offset. But as soon as the mains is not great or has any DC offset, your quiet toroid goes nasty, the core saturates and suddenly emits more EMI than an EI design. So putting that in an external box - especially if your mains is iffy - yields benefits.

A DC Blocker really helped my system out. A cheaper way in solving problem with nasty DC offset on the grid which is very common today.

I think that is the main reason with those devices with either / or powersupplies.
However external powersupplies to my mind are going to offer a slightly larger source impedance due to the length of the Burndy lead… so there might be some cons as well… with all things being equal… perhaps it compensated by external PSUs having generally a larger more efficient transformer which has a lower source impedance.

I do note that this is increasingly a Naim characteristic that other quality manufacturers tend to be not as sensitive to… with some manufacturers opting for multiple localised regulated and noise decoupled mini powersupplies in built in the product.

Selling a 555PSDR with like 6 caps and a transformer in a box for 10000 USD is of course wonderful business. Not to forget. So making the design by purpose work better like this is part of their DNA.


I think you are mixing business model and DNA, although admittedly there is a degree of interdependence.
The Naim DNA so I have been told by Naim at various events, is about audio component decoupling.
This is grounded in good engineering design and electro magnetic compliance design.
The powersupplies are only an aspect of that… but if I am honest I have becomes less and less satisfied at a personal level with the approach with respect to powersupplies… and I am not entirely convinced the approach is optimal for digital componentry such as DACs, streamers etc… where increasingly it’s about decoupled ground domains and EM separation … and locally decoupling of power rails… I do wince when I see powerrail wires routed in straight parallel lines in a digital product.

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You have missed the DR regulators… but in the grand scheme of things relatively marginal, so point holds true.

I suspect the reason is, that the more expensive psu’s have more individuality regulated power rails, this allows the psu to provide dedicated regulated Rails to separate sections within the equipment so that one section ‘tugging on’, drawing power, from the Power rail has less affect on the adjacent sections.

I recall a YouTube video in which Naim touches on this with the Exposed or opened up ‘posh’ Naim phono stage given as the example.

In the simpler PSU’s it separates the power to the power amp from the pre and also breaks the power to the pre into two sections

I think that the benefits of a second 555ps … relate to the micro disturbances each of the transformer secondaries have in operation … with each other - each power rail varies fractionally creating micro disturbance within transformer… You would think the huge reservoir caps would sink this…obviously not…

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To take another example, some users of the EtherRegen (and other switches) add specialist LPSs and report a drop in the noise floor.

How would this work?

(Apart from expectation bias).

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I would say a poor switch mode powersupply may create common mode high frequency currents in the connected equipment… and this might couple into your digital audio.
The other aspect is that a noisy powersupply may modulate the serial line clock so reducing its stability.
However it is worth noting linear powersupplies can be noisy as well, it’s not just the domain of poor switcher mode supplies.

In my HF radio land, which is significantly more sensitive to noise than audio, it is possible, albeit not cheap, to have hugely silent and high performance switch mode powersupplies.

If you are receiving a 10 watt ERP SSB signal from Australia in the UK… you need extremely quiet power-supplies…


It’s reasons like all those above that I don’t write off a product because it uses an EI transformer instead of toroidal or SMP.

They all have strengths and weaknesses which play to the engineering capabilities of the manufacturer. There is a blind faith in toroids and an ill informed hifi snobbery that leads people to think any real linear PSU must be toroid and anything else is cheap rubbish. Which is totally untrue. There are exceptionally good and bad examples of all types. I know some people who’d actually refuse to by a product if it used EI for example. Totally short sighted.



Soulution, which produces some of the best amplifiers available, doesn’t use toroidal power supplies in their products.

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Yes, it certainly looks like reaping it.

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Very small Swedish brand Lejonklou has for years been using dual SMPS in some kind of push-pull mode to get a very low-noise supply and build amps that sound really musical and fine.

And then there is Linn of course.

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Thats hardly a fair characterization of a 555DR. The Naim power-supplies involve so much more tuning than slabbing together a few Linear Tech regs in a box.

The problem is not Naim:s obsession with power supplies, the problem facing them is to bring this knowlegde into a modern/acceptable format.


One of the main strengths Naim have is in their power supplies and the hierachy as you go up the range. They really do make a difference, at a price I must admit.
You can’t hear any reduction in background noise, or I can’t anyway. It just makes things easier to hear and more musical to listen to.
Reminds me of my first visit to the factory when Julian was still there. I picked up a 250 power amp transformer with a warning to be careful of its weight. Yes it was heavy, very.

When I added a 555DR psu to my 272 there was a definite lowering of noise.

The background just droppped away leaving the intended music :notes: right there.

Or did I imagine that?

Is there a technical reason why less EM pollution should flow in my system with a bigger toroid?