NDX 2 review and comparison to PS Audio DirectStream and Metrum Adagio

The folks over at Lexicom Media have a review from October comparing the NDX 2, PS Audio, and Metrum Adagio. I haven’t provided a link since I’m not sure whether this falls afoul of rules, or a translation for the same reason. But google is your friend: for both digging up the article and translating it surprisingly well! Anyway, sharing the info here for those who might be interested and unaware of the comparison.

Two things of particular note:

  1. They clearly didn’t like the PS Audio. They loved Naim, even though it was connected sub-optimally (RCA) while Metrum got the preferred (XLR) connection. For an all Naim system, they preferred it, and for classical they seemed to prefer it. For Diana Krall they might have preferred Metrum… a backhanded compliment if you ask me :stuck_out_tongue_closed_eyes:

  2. They used all three without a preamp, directly into a Bryston 4B^3 Power Amp. No preamp… Some will say this further disadvantaged the Naim, as it should be driving a preamp. But I see it as saying that the NDX 2 can win a comparison against excellent competition even when driving a power amp directly! Very exciting.

I really like the weekly reviews by Lexicom. I think they are well balanced and fairly neutral. even though the reviews are limited to the brands that Lexicom sells, there is good variety in the reviews. Apart from the equipment findings, they are always very specific mentioning the albums they use when reviewing. It always makes me discover new artists and genres.

I agree! For example, I didn’t have K617, which they mention. Am listening to it on Tidal now and enjoying it very much. It’s one of the very few things I get out of most equipment reviews, which can otherwise be dull as paint.

Have I missed something? How do you connect NDX2 directly to a power amp? How do you control volume with this setup?

There is a digital volume control built in, as it’s a requirement for AirPlay certification. Naim recommend you disable it for best sound quality.

Direct connection to a power amplifier is not recommended. It is only there for Airplay and for best performance you’re best off using fixed output into a proper pre-amp input.

Well that’s interesting, first time I hear about it. How is the digital volume control implemented in NDX2? I’m in a process of possibly changing my passive ATC’s to active ones. I thought 272 would be the only option in Naim lineup (for one box solution in front of them) but it seems NDX2 would work also. Maybe I need to arrange demo of both.

Could be an interesting demo. The official Naim line is bound to be that you should disable it and use a proper preamp, but then, you wouldn’t be using a Naim power amp, so any synergy there becomes irrelevant. Also, you’re getting a better streamer, which might outweigh any downside of the inferior volume control.

There are two ways: using digital volume correction to the stream prior to it arriving in the NDX 2, and using the digital volume control built in to the NDX 2.

The first way, in Roon for example, takes a 16-24 bit sample, converts it to 64 bit floating point, before converting it back to 32 bit integer at the Naim input. Assuming you have less than 8-16 (depending on your starting bit depth) bits of attenuation, it is perfectly lossless.

The second way, which is required for Airplay 2 certification, is not disclosed as of yet. I wouldn’t be surprised if it’s as good as Roon’s way, but I can’t say.

Either way the filtered output is fed from a 10 Ω output impedance on the NDX 2 into a power amp with a minimum input impedance of 10 kΩ. The NAP 300 DR has an input impedance of 18 kΩ, so should be fine. This all, provided the NDX 2 doesn’t introduce ultrasound harmonics above 50 kHz, which of course it won’t do if you feed it data at lower than 96 kilosample per second rates. I don’t know what would happen for data at higher rates (i.e. if the NDX 2 filters those out, or doesn’t in anticipation that a preamp will do so).

People much more knowledgeable than me on this forum (e.g. Richard Dane) have been crystal clear that all of the above does not translate to an optimal configuration. I’ve double checked this with Naim support and they’ve completely backed Richard and others up. So, I wouldn’t do this if I owned a Naim preamp. But I don’t, yet. I will do this at first, and look to purchase a Naim preamp (perhaps a used 82 or 52) at the first opportunity.

One of the things that caught my mind about the Lexicom review is that they did use this sub-optimal configuration in their comparison, and yet they felt the NDX 2 was better than the PS Audio DirectStream and on par with the Metrum Adagio. This is astonishing since both of those were configured in their optimal configurations (i.e. they both have built in preamps and are specifically designed to drive a power amp directly, unlike the NDX 2).


Thanks for a comprehensive reply Pedro.

I don’t really know why Naim would discourage people to connect NDX2 directly to poweramp. Reason is probably only commercial, to sell more preamps. I can’t think of no other reason to this. With properly implemented variable output, one would think that preamp is only unnecessary extra step in the signal path(?) And Naim usually does things with great care.

But I will definitely test this when I the active SCM19A arrives to my dealer. Also sorry for hijacking the thread.

Do the demo and decide fit yourself. Much as I’d like to declutter, my attempts to eliminate a Naim pre from my system so far have been unsuccessful.

Yeah, I had 272 in my mind but after the release of new streamers, I can’t help having a feeling that 272 feels slightly old in comparison. It’ll probably be updated soon and buying it at this point feels awkward. There’s plenty of them available second hand though.

Correction: running the NDX 2 now and I can’t get Roon to allow volume control. So there seems to be only one option: the built in volume control in the NDX 2.

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