Naim NDX: the performance upgradeable high-end network player

Uncategorised By Sep 03, 2010

3 September 2010. Salisbury, UK. Naim today launched the NDX: Naim’s first dedicated network player. Designed and engineered to integrate into Naim’s range at a similar quality level as Naim’s innovative multi-award-winning HDX hard disk player and CDX2 the top selling high-end CD player, the NDX is performance upgradeable in stages as the owner demands. The NDX is performance upgradeable by the addition of a XPS or PS 555 power supply and/or Naim DAC.

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Product Overview

The NDX is a high-end network player designed to match Naim’s reference series products. For an existing Naim owner one might expect to see a NDX sitting in a Naim Fraim equipment support system alongside a CDX2 or CDS3 CD player. Naim envisage the owners of the NDX using it, primarily, as a high-end quality streamer playing back music ripped from CDs or hi-res music downloaded from the many online stores.

Technically, the NDX draws significantly from the hugely successful Naim DAC. The innovative and SHARC DSP-based buffering with fixed clocks is utilised along with 16 times oversampling and Naim’s proprietary, low-generated noise, digital filtering algorithms.

The NDX adds far more to a system than just streaming. It includes three S/PDIF digital inputs to support connection from computers to set top boxes to CD players.

It includes internet radio – the radio of the future –supported by vTuner’s five star full service. Search for stations by genre, location or just simply by name. New stations add automatically to the searchable database. Add special favourites or less common feeds to ‘added stations’ via the special Naim webpages.

Connect an iPhone or iPod digitally to allow the NDX to control and play all the stored music, podcasts or audiobooks. Play music on a USB stick, even hi-resolution WAV or FLAC files, with full onscreen control.

Control the NDX with the front-panel buttons, the supplied remote control or an iPhone or iPod Touch running the optional n-Stream app. The app also allows control of a Naim system’s inputs and volume.

Choose the optional FM/DAB module to add terrestrial radio stations. Maybe your favourite radio station has yet to start its internet radio stream.

Key Features

• UPnPTM Network Player with Gapless Playback

• Internet radio with vTuner 5* full service

• Three S/PDIF inputs 24bit/192kHz

• SHARC DSP and buffering with fixed sampling rates

• Naim proprietary 16 times oversampling and digital filtering

• Optical isolation of all key elements

• Front-panel USB port for USB stick playback

• Apple authenticated digital iPod/iPhone playback

• Optional FM/DAB module

• Ethernet network connectivity for reliability. Wireless connectivity for convenience.

• Streams and plays WAV, FLAC, AIFF, AAC WMA, Ogg Vorbis and MP3

• Buffered Digital output on 75Ω BNC connector

• Performance upgradeable with XPS or 555 PS power supply

• Performance upgradeable with Naim DAC

• Linear power supply — 200VA toroidal transformer with four secondary outputs.

• Separate power supplies for digital, analogue, and DSP and clock

• Ground selector switch for optimum performance

• Naim reference non-magnetic, low-resonance low microphony case

• OLED display for high contrast and easy visibility

• British design and build


Just over two years ago, when Naim launched the innovative HDX hard disk player there was a shortage of streaming players and a real dearth of DACs. Now, there is no longer a shortage of either of these but there is still a significant shortage of players that deliver a true musical performance and not just shiny Hi-Fi sound.

Delivering music over Ethernet or Wi-Fi is not difficult, but to do it well requires an attention to detail that is still surprisingly rare in today’s market.

It requires control over every part of the chain possible. CD rips have to be undertaken correctly – a CD rip must be a secure rip. Storage needs to be fast, reliable (and of course backed up).The network needs to be well set up, with low collisions, and plenty of bandwidth.

Finally the player should be designed to be low jitter, reject the RF and other aberrations from noisy power supplies, mobile phones, the general environment and of course the EMI from computers. This is in addition to the standard audio requirements of technically measuring well, having a well-designed and hence good low-impedance power supply and good choice of components.

These are the basic building blocks. Then the attention to detail really counts.


The NDX has galvanic isolation between key sections of the circuits. This reduces the noise transfer to the analogue domain from the digital circuits and connections. Whether the NDX is playing from internal or external digital sources, the digital data is isolated from the DSP and in turn, the DSP is isolated from the master clock and DAC. There is maximum isolation between digital sources and analogue output. The power supplies for each section of the signal path are also independent. Four separate secondary windings feed four separate power supplies for isolation.

Naim’s buffer or memory method of jitter removal relies on a simple concept: the audio data clocks into the memory at the incoming inconsistently timed rate and then a precise clock controls the data out of the memory and into the DAC chips. Selecting the master clock that best matches the average incoming clock frequency, controls the rate at which the memory fills and empties. In this way, the data entering the DAC chips is completely isolated from the incoming jitter.

The NDX uses the same 16 times oversampling filter as the Naim DAC, implemented in the SHARC processor. The chosen filter is a modified Butterworth filter to which additional poles are added to prevent too much phase shift occurring within the audio band. The filter runs as efficiently as possible, using only five lines of assembly code. This ensures both low arithmetic noise (fewer additions and multiplications that cause rounding) and low power supply noise (since the DSP draws less current when it is not calculating).

The DAC in the NDX is a Burr Brown PCM1791A. It is used in 16 times external oversampling mode and runs at a maximum sample rate of 768 kHz.

The analogue output filter is multi-stage seven-pole filter. The design uses Burr Brown OPA42 opamps to perform the filtering; these are single chip opamps so a total of six are required. There is a plethora of audio opamps available but after many hours of listening tests, the OPA42 delivered the finest sound quality in this circuit. A combination of Sallen-Key and multiple feedback low pass filters are used to implement the seven-pole filter.

Reducing power supply (PSU) noise has long been part of Naim’s design philosophy. To increase perceived and measured dynamic range, PSU noise in the NDX is reduced to an extremely low level.

The NDX can be powered from its internal (integrated) PSU or as an upgrade an external Naim PSU; XPS or 555 PS.

The reservoir capacitors are larger than would typically be used to reduce the unregulated voltage noise and provide increased short-term current capability. The four separate PSUs form part of the electrical isolation of the Digital DSP section from the DAC chips and analogue circuits.

Low noise LM317/337 regulators smooth the unregulated voltage from the reservoir capacitors. Voltage supplies to many of the digital circuits are double and in some cases triple regulated to further reduce noise. Quadruple regulated if using an external supply.

When the PSU upgrade option is used with the NDX, power supply separation is maintained as the external power supply also has independent power supplies and ground connections. It also provides a significantly larger toroidal transformer and larger reservoir capacitors to further noise reduction.