Mu-so amplifier design

The design of the Mu-so amplification is, obviously, quite a bit different from the standard Naim components. It seems more related to their Bentley designs. I read somewhere that it somehow uses the digital signal to more directly drive the speakers. I’m wondering if there’s a more technical discussion of technologies used than what is discussed in the marketing literature.

I believe the amplifier is Class D, as used in the Bentley stuff. The speakers are actively driven, so separate amps for bass and treble. It’s basically a car stereo in a little box.

I read somewhere the Steve Sells didn’t think Class D would work for high-end audio. Clearly, their opinion has changed, but I wonder what they did to get there.

I suspect their opinion hasn’t changed. The real “high end audio” from Naim still doesn’t use Class D.

The experience gained from developing the DSP for the Naim for Bentley system led to the Mu-So where DSP is used to give a “big” sound from a small box.

Class D is ideal where you need plenty of power with high efficiency and where packaging is very tight, so it suits the Mu-Sos and the Naim for Bentley system very well.

Even back in my days at the factory there were class D amps being designed and evaluated in R&D. I think that overall, Naim still reckon that regular amplification gives best performance where you have the space and you don’t need so much efficiency, which is why we haven’t yet seen class D appear in a NAP yet.

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Thanks for the note. The marketing makes a big deal about the increase in processing power, but they don’t really explain what that buys you. Do you know of a more extended discussion of how they approached this design? Obviously, I’m not really interested in trade secrets, but my understanding is that the Mu-so has the “Naim sound” but using a very different approach than what is used in their other components. It would be enlightening to learn how they achieved that.

BTW, I’m a new Mu-so 2nd gen owner, so I’m definitely in the gateway phase of the Naim universe…


As I’m not an engineer, I’m not the best person to explain the design, so it’s probably best to ask Naim directly.

Muso isn’t high end audio, in my view (yes, having heard it - that is Muso 1) just a better-than-average boombox - actually darned good for a boom box, and I’d have one if it weren’t for the price and dust trap, but not really hifi let alone high end. Personal opinion of course.

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This is a follow up to a previous post. I saw somewhere that Naim is using direct digital amplification, which is a way of using a digital stream to directly drive the speakers. I found an article on this type of approach produced from NAD, which I believe is called DirectStream or something like that. I’m puzzled that Naim doesn’t talk about this technology more. It’s seems like a promising approach for digital-focused music, which is the case for Mu-so. I speculate that they may have licensed that technology from someone else.

I ‘m definitely enjoying the Mu-so 2nd gen, so I’m curious to understand how it works.

Kevin, I’ve moved your post to your original thread as there seemed no reason to start a new one on the same topic.

… yet :wink:

besides being brilliant, its a gateway product, you may find :upside_down_face:

Joking aside. I can see converging technologies as and when and if Naim master them. Trickle down effect in play. In 5 years a NAPD500DSP anyone? In my long relation with Naim many questions I asked was met with “never” until it was possible :grin:

You can find a whitepaper at NAD It sounds similar to what Naim alludes to what they are doing for Mu-so. I’m intrigued because it’s very different approach that carries a lot of advantages.

The standard hi-fi system will remain niche. The question is how to take those audiophile values and engineer them to work in different environments. Naim is pushing the envelope in that market.

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Adam, unfortunately forum rules make that impossible. If you wish to read it, look for the Direct Digital White Paper, although it comes across more like an ad.

Hi Kevin – I don’t think Naim is doing anything particularly novel here. As others have mentioned, the Muso uses Class D amps, an efficient way of getting decent power in a small package. In the Muso you’ve effectively got 6 amplifiers so Class D makes sense to keep size, weight and cost down.

Naim make extensive use of DSP (Digital Signal Processing) to tailor the sound of the Muso, to account for its placement (eg boundary or open space) and to provide a loudness function for lower volumes. It also implements crossover functions in DSP so the amplifiers serving the treble, mid and bass only deal with those specific frequencies.

I suspect the Muso is just the implementing some of the usual functions of a Class D amp in the DSP section. In most Class D amps, an analogue input signal first needs converting into a digital PWM (Pulse Width Modulation) signal using a PWM modulator. This PWM signal is used to drive the output stage before final low pass filtering. In the Muso, all the processing has already been done in the digital domain so it would make sense for the digital PWM signal generation for each amplifier to be integrated into the DSP section.


I finally found a post from Naim discussing the Processing chain. According to this article on Direct digital amplification, the PCM signal is processed by DSP and then sent directly to the output stage. So, it’s apparently different than the standard Class D amplification as their no conversion to analogue. They also have some a special feedback circuit. So, what strikes me from the Naim post is that it sounds very similar.

Clearly, other manufactures think this approach can reach audiophile standards. Naim has said in other posts that standard Class D isn’t good enough. So, maybe there adopting something along these direct digital amplification lines.

The relevant question there is what was Naim talking about: i.e. “good enough” for what? I think that at least in simplistic terms there is a distinction between what Naim thinks is good enough for boxes that aim to be pretty high up the hifi ladder, and what it thinks is good enough for a far more basic replay unit, whether it be Muso, Qube, or something to play in the confines and limitations of a car. And however much the limitations of D-class or whatever may make Naim not use it in the hifi gear, I suspect the Muso would simply not exist without it as otherwise it would be a lot bigger.

Of course, that comment would have applied to the time it was stated, and whatever Naim thought of D-class at any past point in time need not necessarily mean that with improvements it will never be possible for them to develop something that sounds as good or better than their existing amps - a case of never say never.

I have links embedded in the response above, but it’s not clear if anyone can actually see them.