nDAC with 555PS DR or 555PS

I think the merits of DR vs non-DR PSs depend on which PS it is as well as which box it’s being used on. When I had an original SuperNait powered by a HiCap I took up the opportunity to have it DR’d and that was the best value Naim upgrade I ever made, a major improvement in SQ. I also had a XPS powering a nDAC done and whilst that was also an improvement to my ears, it was much more marginal.

Oh and the 250DR is just miles better than the previous 250 (he said from behind the sofa!)

Roger

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I would like to make a correction, the DR at the power amp had least of this dynamic booster effect if any or just a placebo, though i did not test all possible combinations with it as it was upgrade straight out of the box for me. It is also a different amp (using the new transistors and perhaps other new components. So to be more precise, if I need to attach a number, would say 10pct for source, 10 percent for pre and 2-3 pct for the power amp if any.

I am not an audio engineer so please do not laugh at me, I need some pro help to demystify this DR effect, that concerns many of us. So far, came to the conclusion that some people are happy with the DR at the source and pre-amp and some not, right? Also all people are happy with the DR at the power amp. If so could it be the speakers making the difference. The effect is most noticeable at about 400-600Hz, which is about the mid range of classical guitar. Looking at my speakers, they have a high capacitive load at 433Hz (-41deg phase shift and 6.54Ohms impedance), hmm, could that be it? so how could be and is it possible that the output capacitance of the loudspeaker is fed back into the control loop amplifier and form a single-pole lowpass with the pre-amp output impedance, that further transfers the same effect to it’s power supply output impedance causing phase shift, that further cause instability in the control loop, when there is not enough phase safety margin. And is it possible that in the older non-DR versions this phase safety margin is bigger, so they are less speaker load dependent. On a separate note, if that could be really the problem, is it fair to assume, in the new classic series the power supply for the source and pre-amp was deliberately made non-DR? at least I cannot see it as DR? maybe i am wrong? @Richard.Dane can you help too?

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Sorry BBK, I’m not an engineer. Perhaps if @110dB sees it…?

The NPX300 contains 6 DR regulators.

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Hi @BBK

Here’s a quick answer, I hope it helps.

NPX 300
The NPX 300 has 8 DR regulators, with 6 separate grounds. The separate grounds join at the appropriate PCB location for the respective product that is being powered. (for streamer, pre-amps and streaming pre-amps)

Power amps
The speaker load impedance irrespective of a regulated PSU in the power amp will have an effect on the performance. Power amps have feedback, the feedback is taken from the output. Loading on the feedback changes the phase shift of the feedback. Engineers in all companies work hard to ensure there is adequate ‘phase margin’ for closed loop stability irrespective of load. Lots of compensation is great for stability but makes the amp sound dull, too little compensation sounds great but could be susceptible to very high frequency parasitic oscillation (typically 1-10MHz region). The PSU of the power amp and power amp output stage appear in series with the speaker signal current.

Certainly the high frequency impedance of a power PSU will effect stability. Detailed circuit and PCB design is needed. Simply adding capacitors on the power amp rails lowers the impedance but can push noise into the ground they are connected to. At Naim the connection from the built-in DR regulator is connected as close as possible to the power amp output stage.

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I’m sure DR is superior to non-DR technically but after having a non dr 555ps on my NDS and the pleasure it gives me as the joint best sounding source I have ever heard (with myLP12), I cannot imagine ever wanting to “upgrade” to DR. Perhaps it’s just the 100% or more premium for used items or the eye watering cost new (for me)? Certainly non DR is for me is not wanting in terms of SQ. I do however find it very interesting that some prefer DR and some don’t. There are obviously many parameters at play here but I am a firm believer in having a balanced system and that such a system can in many cases compete with the best of the current technology on an even playing field. Of course some will disagree :nerd_face:

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Dear @110dB , Thank you very much for your time and input. As far as my brain cell can understand, the better the PS is the more critical is to the loudspeakers load, and that could be one reason for the “DR effect”. I am happy with my DBLs and a non-DR versions, think this will end the discussion for me :slight_smile: and hope will also help others in optimizing their systems going forward. I think people with ND555 have greatest flexibility and luxury to have one DR and one non-DR and swap them to find the best SQ.

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@IainO , thank you for the input too. Given the conclusions so far, would be better to also have NPX300 without DR regulators, so people can, can have options :slight_smile:

@Paul52135 , if your source is better with non-DR, I think your pre-amp would be also be better with non-DR. I wander which you have at the moment?

My preamp still has its old 52PS :grin:. I suppose it’s possible to DR with a Supercap DR but I won’t be trying it. I wonder if anyone else has?

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I stand corrected by Steve on the 6 vs 8 regulators.

I said 6 because that’s what naim’s own (old) website used to say, just check google

It’s also on many reseller sites, such as Sevenoaks….

You can see 8 regulator boards in that pic.

So it seems naim have shot themselves in the foot by releasing launch materials which were incorrect! Now all over the internet as 6…

Marketing and R&D are two different universes these days.

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I am considering looking for a 555PS to add to my nDAC.
The idea of getting an NDS to use as a DAC remains as an option later on.
The source is a Jay’s Audio CDT2-MKIII, I do stream very infrequently using a Wiim Pro as a network bridge for Qobuz. The rest of the system is DR with a NAP-300 power amp.
The question remains to go DR or non DR with the 555PS

Non DR it sounds so much more coherent and musical.

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Non dr can be serviced at Class A and should be cheaper. A few reckon a non dr sounds better, that maybe true, but id need someone to explain why that should be. Put a 555dr on my ndx2 and was surprised at the improvement. A friend of mine prefers her xpsdr on her ndx2 though.

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I ended up going 555PSdr and found a fairly freshly serviced unit and over the last 2 weeks has run in nicely; as was said somewhere, with the 555ps, the combination is a complete bass monster!!

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Great it wotked well for you. After all maybe is a speaker dependent outcome.

Great that the sound is still improving as the relatively newly serviced 555PS settles in

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Pretty sure it’s bias there.
Freshly serviced 555 is always better then tired kits.
Dont underestimate service due to older psu’s especially non dr.
Preferring a bare ndac over powered ones tels
a lot.