In the (one would hope very unlikely event) of software VC failure defaulting to max volume, when you can leap to the rack to hit mute or grab the VC knob, you equally could leap to it and hit the power amp power switch - it is another physical way to mute the output in an emergency.
Edit: Not sure why this targeted HiFi Man
Totally agree … it could be quite a big boom !!
I had same discussion with a Nagra dealer…I told him that I have only one (!) source left and that a pre-amp could be skipped in my quotation. He replayed: NO way- he tried a 25k Nagra DAC w/ volume control directly to a Nagra power amp. That was not the same sound as the second best DAC feeding a pre-amp. His finding: buy the best pre amp even if you have only one source.
I very much doubt it’s going to sound optimal and be totally safe.
For one thing the matching impedances are probably all over the place.
The input impedance of the NAP500 is 18k ohms
The output impedance of the ND555 I can’t find specified, however the input impedance of the NAC552 is 47k ohms whilst it’s output impedance matched for Naim NAPs is <50 ohms with a load impedance of 10k ohm minimum …
So to me I would expect the ND555 is optimised to drive a NAC load, not a NAP load… so it will work, but iit will most likely not be sounding any where near optimal. And if not optimal why bother with a 500 series product, or any Naim product for that matter.
I don’t quite understand why some forget the importance of impedance matching with preamps, which is a crucial activity for the amp to sound its best.
The “mundane” volume control and input selection functions of a preamp are obvious. The signal’s characteristics are not. I think that the desire to “eliminate an expensive volume control and input selector” is what drives this way of thinking - ignorance.
Even Chord make preamps and they recommend them with their DAC,s like DAVE which have volume controls.
The standard reply would be, “Of course they want to sell us an expensive piece of (unneeded) equipment!” 
Impedance/drive capability of course is indeed a crucial factor, and it may be that the ND555 isn’t suited to feeding a NAP’s 16/18k input impedance. However, as you indicated the information isn’t readily available, and I’m not sure that what information is available really supports concluding it is not.
In the absence of such indication from Naim I would certainly not expect the ND555 to be have the same capability as, say, Dave, with its very low output impedance and ability even to drive speakers direct let alone being quite happy and capable of driving virtually any preamp or power amp: However, the ND555 might yet be quite capable of adequately driving a NAP’s input, even if not intended that way.
Of course that is not to say that it wouldn’t sound better through a NAP as Naim intends it to be used, though I’m not sure that anyone has yet indicated an audible difference, let alone in what way.
Aside from that, with some streamers or stand alone DACs a different reason for not using directly into a NAP would be if they don’t have a low pass filter to remove high ultrasonics, which I understand the NAPs do themselves include, however IIRC the ND555 does do that.
I haven’t seen anything recommending that Dave be used with one of Chord’s preamps in preference to feeding a power amp direct, and certainly the manual for Dave makes no such preferential recommendation. Meanwhile on their website Chord says that Dave is “perfect with” followed by the names two power amps… Of course when anyone wants analogue input options as well as Dave, Chord would recommend using one of their own preamps.
Too late to edit, that should have read “the NACs do themselves include”.
From the preamp part of the website, they seem to be recommending their dacs, . Anyhow best to listen for your self. I tried to duck buying a 252/SC dr, with a Dave into 300 dr, sounded devoid of life, imo. But worth trying.
The same here, and Chord refers to Dave as a “digital preamp”…
That’s where I went to check upon reading your previous post, and could find nothing recommending or even hinting that Dave is best connected though one of their DACs… Just double-checked and still can’t see anything, though on the Dave info given under ‘‘reference series’ page linked from the preamp page it says this: “The device’s lossless digital volume control outputs the signal direct to your power amplifier for the purest experience.”.
Of course, as has been mentioned on, I think, the Is the pre-amp a thing of the past? thread amongst others, in a Naim system the preamp may be the key to the ‘Naim sound’, and without it you lose it.
This has moved on a bit from the ND555 - however the same consideration might apply if the ND555 is sufficient an electrical match to NAP500 to drive it effectively, in that the absence of a NAC may mean the absence of the ‘Naim sound’. But as someone said earlier, assuming the OP has access to a dealer to audition, he/she can try with and without.
Well when i look at their Ultima preamp on their website…its a £30k preamp…it says perfect with a number of their products like Dave and Blu2. I expect my hifi dealer and manufacturer to be honest. If i do not need a £30 k preamp, do not mention them together on the same web page. Thats all.
Yes, just as Dave page says perfect with some of their power amps… Taking what else they say into account, i take that as meaning that by being completely transparent and neutral the Ultima is as good a quality as Dave and so would be a perfect match with Dave if you need to combine Dave with analogue sources, or if the want the frequency EQ adjust controls that the Ultima also offers.
Naim products pages also suggest upgrades you don’t need. For example, suggesting a $15K 555PS as power supply upgrade, plus SuperLumina and Powerline for another $5K or so, for my $7500 NDX2.
Yes it’s the only way.
Chord makes a pre-amp in a case that matches Blu2, DAVE and Etude. I asked about it and was told it was useful if I wanted to use analogue inputs such as the matching phono pre-amp. DAVE direct into Etude was the recommendation for me as I have no analogue sources.
When I auditioned The Etude I did so with and without Chord’s statement pre-amp. With its tone controls defeated I couldn’t hear any difference. The tone controls are exceptionally good, but at £30k I decided I live without them. At home I tried a Linn KK pre, but decided i could not hear any benefit.
So my Chord system is a 3 box - transport, DAC, power amp arrangement.
I understand with Naim, the NAC is recommended, but I don’t think it is necessary with Chord. I did at one time use a Naim DAC into NAP200 and relied on software volume control, seemed to work OK, but I understand the “boom” concern, never thought about it at the time.
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