Tech Talk: dCS

A flex-rigid PCB is a single printed circuit board made up of multiple pieces, which are connected by continuous flexible conductors.

Utilising a flex-rigid PCB allows us to have what would otherwise be multiple PCBs (one board for signal processing, another for the digital-to-analogue converter, another for I/O and so on) unified onto a single board. This means there are no interconnects between separate PCBs.

This removes any possibility for slight differences in how interconnects are routed – a few millimetres difference in how a ribbon cable is placed can have effects on the performance, for example. Using flex-rigid PCBs allows for short signal paths for key signals (such as clock circuitry, analogue signals), helping to maintain signal integrity throughout the product – all of which helps to ensure optimal performance and sound quality during playback.

It also reduces the risk of crosstalk and helps to further improve reliability. An additional advantage is that the flex-rigid PCBs are easier to test.

Flex-rigid PCBs are challenging to manufacture – to our knowledge, we are the only audio manufacturer to utilise them in our products – but their use brings several benefits.

The Lina DAC X PCB contains over 2,000 surface mount components on a 12-layer flex-rigid PCB, which folds four ways to fit the Lina DAC X chassis.

Chassis Design

As part of the Varèse project, we investigated how we could improve our chassis design. Typically, the chassis of an audio product would be made from multiple individual panels – one for the top, one for the bottom, and one for each side – which are then secured together. Previous dCS products have used separate panels milled from billet aluminium, which are secured together with no visible fixings.

Our latest products, including Lina DAC X, feature a more ambitious, complex chassis. The main structure of the Lina DAC X chassis is constructed from just two parts: the top and sides are all milled from one single billet and the base, front and rear from a second. Reducing the number of panels means a more electrically sealed environment, as there are fewer gaps in the chassis for any unwanted interference to get into or out of.

It also allows us to incorporate other elements – such as mounting points or standoffs for PCBs – into the metalwork of the chassis. Other designs separate PCBs from the chassis with plastic or metal standoffs, which are pressed into the chassis and then secured with self-tapping screws. This can create some variance in how far the PCB is mounted from the chassis, which can have performance implications (consistency of board height compared to the ground plane – the chassis – aids performance).

The standoffs within Lina DAC X are machined from the same aluminium billet as the chassis plates (including screw threads), so there is no variance in their height and no self-tapping screws needed. This provides great consistency of the height between the PCB and chassis.

The chassis design of Lina DAC X, coupled with the use of a flex-rigid PCB, has also allowed us to isolate power supplies from other components. The top plate of the unit includes a significant aluminium channel that runs along the centre line of the product. Viewed from the front, the left-hand side of the channel houses the PCB, and the right-hand side houses the mains transformer. This separation is made possible thanks to the flex-rigid PCB keeping all of the electronics housed in one half of the chassis, leaving the other half free for the transformer.

Ring DAC

Like all dCS products, Lina DAC X utilises several technologies that are unique to dCS – some of which have been carefully honed and refined over many years. The most notable of these is the Ring DAC, a bespoke D/A converter that is found at the heart of all dCS DACs and music players. It allows the Lina DAC X to convert signals to analogue with vanishingly low levels of distortion.

This low distortion level is true at any signal level, even at low amplitudes (such as quiet musical passages or delicate reverb tails) where other DAC architectures will often lose fine detail to distortion. The Lina DAC X benefits from our advanced Mapper algorithms, which distribute digital audio samples to the Ring DAC current sources at ~6MHz, ensuring no unwanted interactions between current sources occur.

The hardware of the Ring DAC is composed of an array of 0.1% precision metal film resistors, each with an accompanying latch to activate or deactivate the current source based on the Mapper. The latches are fed a clock signal generated by ultra-high quality VCXOs (voltage controlled quartz crystal oscillators) that operate within our bespoke Phase Locked Loop circuitry – a section that other manufacturers simply use off-the-shelf chipsets for.

A number of elements inside the Lina DAC X are locked to the VCXOs – such as the switching power supply elements and the front panel display – to ensure no unwanted noise is generated inside the product. This means listeners do not need to perform tasks such as turning the display off to achieve the best sound quality.

Lina DAC X is an important product for the company, as it brings the core values and performance that dCS has to offer at a price that introduces the brand to a new generation of music lovers.

Manufacturer

Data Conversion Systems Ltd

dcsaudio.com

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