NAIM NDX User Manual

Also see for NDX -: Connection guide Guide Supplement Manual Update guide Quick start guide

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NAIM NDX User Manual Manual pdf 8 page image

Copyright Naim Audio 2010 Page 8 of 8Analogue stage filter capacitors that work in the audibleband are prone to microphony, so susceptible componentsare lifted from being in direct contact with the board tominimise this effect.PCB design for digital circuits is as critical to performanceas it is for a high-end power amplifier – possibly moreso – and different techniques are required for digitaland analogue board design. There are high-speedDSPs, high-resolution digital circuits and low noiseanalogue circuits present, all of which require differentdesign approaches. In the NDX the DSPs are placedwell within the boundaries of a six-layer PCB. Multiplepower pins are decoupled using multiple decouplingcapacitors mounted on the bottom of the board, and theDSP also relies on inter-plane capacitance to providelow inductance decoupling. External peripheral devicessuch as the SDRAM are placed as close as possible tothe DSP ports to minimise the loop area of high speedcirculating currents. All high speed traces are measuredand resistively damped accordingly to ensure that digitalsignal edges are not subject to ringing since ringingradiates high frequency electromagnetic energy thatcould affect the analogue circuits.The master clock drivers and timing gate are decoupleddifferently to slow-speed PCB design. For bestperformance the decoupling capacitors are placedtopside to avoid using the inductive PCB vias. Decouplingtraces dominate the topside, being as wide and short aspossible since every millimetre of PCB trace length hasa significant effect when clock signals are at 24MHz withnanosecond rise times. All high frequency traces aresandwiched on the central layers of the PCB where theyare shielded by the ground and power planes that createthe high frequency return current paths. Outer layers areused for low frequency signal and clock decoupling.In the analogue circuits, different techniques arerequired again. Here large planed areas of conductor aredetrimental to sound quality and are replaced with the starground techniques that can be found in all Naim analogueproducts.Gapless playbackThe NDX supports gapless audio playback with bothcompressed and uncompressed audio formats. In thismode there is no two-second gap between tracks, whichcan be so annoying when listening to a live recording or aclassical music recording where the microphones remain‘open’ between movements.Digital outputA single S/PDIF output is provided on the NDX via a BNCconnector, chosen for best sound quality and impedancematching. The S/PDIF output is both buffered andisolated, the isolation being achieved using a high qualitypulse transformer. The buffer, which is used to drive theS/PDIF currents through the pulse transformer to thedigital receiver, isolates the DSP from the high transientcurrents required for S/PDIF output. As the S/PDIF signalis RAM buffered in the same way as the digital data goingto the internal DAC chip, the same level of jitter removal isapplied whether the output is analogue or digital. Digitaloutput is switchable and is should be disabled when theanalogue output is being used.

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