mdxs – the source


mdxs – the source

By Kilian Mattitsch, Martin Hess, Georg Müller / Website

This digital audio player achieves an excellent sound quality – our main interest – thru designated power supplies for as many accessible and reasonable sections of the circuit. Most linear regulators are built from scratch and all is backed by a generous power supply unit.

Starting at the part which creates the analog signal, the power supply of the Hifiberry DAC+ Pro’s analog section (AVDD) is directly connected to a 3V3 SuperTeddyReg (the best linear power regulator we heard) bypassing the onboard LDO.
Second we split the digital section of the DAC, supplying DVDD and MCLOCK each with a 3V3 single LM317 regulator (additionally shielded from power rail noise by a VBE filter).
On the Raspberry Pi board the CPU and the USB ports get ample power thru their own 5V single LM317 regulator.
All regulators are powered by a custom PSU with a large center tapped toroidal transformer and a CRC configuration at its smoothing capacitors.

This design separates noise from

– power hungry or radiating peripherals
– the “gHz” clocked CPU
– the digital processing section of the DAC
– the sensitive “mHz” clocks of the DAC
– the output – the “kHz” analog signal formed in the DAC’s analog section
– and of course mains AC “Hz”

to gain the cleanest hens most sonic audio signal.

Further considerations on star ground, heat sinks, a simple and funny way manufacturing small circuits, and the part assembly in general lead to the overall design of the Copper Plate DAC series.

Which parts where used for this project?

Casing:- the copper plate – main frame, heat sink, star ground; - top & bottom 2mm aluminium plates; - nuts and bolds.Of the shelf circuits:- Raspberry Pi Mod B+ single-board computer; - Hifiberry DAC+ PRO i2s sound card; - 3V3 SuperTeddyReg linear power regulator for AVDD (pricey; alternatively we build tracking preregulator with LT1086CTs).PSU main components (in order of appearance):- Talema 80VA 2x 9V transformer; - 6A Schottky diodes; - Panasonic 5600uF/35V; - 2.2 ohm 7W resistor; - Kendeil 10000uF/40V;Home made circuits:- 2x 5V LM317 single regulators for CPU & USB; - 2x 3V3 LM317 single regulators w/ VBE filters for DVDD & CLOCK;

Do you have a guide available that allows others to build this?

Anything else you like to tell us about your project?

Why DIY? We like to understanding the objects which surround us my making them ourselves. Doing that we have the freedom to select what we want to understand (we are layman in the end), what we built knowledge upon, and how far we venture. Several sources inspired us for our project. Our liking of the very best of British Hi-Fi equipment from the 70s & 80s (especially how it reproduces music and the technical strategy inside to achieve this) led us to the importance of designated power supplies to supply & isolate each circuit section's workload and behavior. The work of several DIY enthusiasts informed us about how to built good linear power regulators or – in the case of Teddy Pardo – where to get the best. We listened to all of them. For economic reasons, and obviously AVDD being most beneficial, what goes where is prioritized. Finally the popularity of the raspberry pi led to great audio software and DAC boards. We like the UI of Volumio and, from all the DAC boards we listened to, we liked the sound of the IQaudIO’s Pi-DAC+ and the Hifiberry DAC+ PRO the most.