The MCU we are planing to use for the FDAC Digital board has a SDcard interface, I was considering adding a SDCard reader to the FDAC so that later we might release a software update (lots of work) that could read and write to the SDcard - Mainly to be able to offer an all in one recorder / or test system.
This opens a whole bag of hurt - dear Adam here on PFM will be rolling around in discomfort!
I can see how the varying CPU process produces different RF / Jitter spectrum and this is a fact of life - what's not tolerable is that this makes its way into the Analogue domain. I myself have heard such effects myself and am not proud - it indicates design limitations with the audio system and as an audio designer I have to share the blame.
Computers will radiate all kind of nasties - they are horrid is this regards so we need to accept this as a fact of life and tackle the problem head on.
I slept on the ideas last night and really want to design this USB Detox (
) interface as I'd be avoiding the elephant in the room to ignore the multitude of problems posed by connecting a computer to the audio system. I've always stressed that the RF and Jitter should be dealt with BEFORE they are allowed to enter the DAC enclosure - this holds true for the MDAC and FDAC.
The design is a quick task, the production will be interesting, but I'm really keen to "send a simple design down the production line before the FDAC PCB's" so it makes this little project even more interesting.
If there is significant interest then it will take less then a week to design the PCB.
As each USB Hub device only offers a certain "limited" level of attenuation I'll cascade 3 devices in series each with there own PSU and Clock interface, this will add extra cost - but its the correct way to design the board.
Lets to a proper job of this
I'll use these RF screen tins for each Cascaded attenuation stage and the Master clock circuit:-
http://www.teko.it/en/prodotti/famiglia/RF/serie/49
So the design will look something like this:-
USB input
RF Filtering
1st Hub
RF filtering
2nd Hub
RF filtering
3rd Hub
USB 2.0 480Mbps USB output (Non Isolated) + RF Filtering
USB 1.1 12Mbps galvanically isolated USB output + RF filtering
There will be two toggle switches to enable the Clock-lock interface + Spectrum decorrelation mode (Enables a random spread spectrum clock source).
Development fee GBP50 + unit sold at cost say around GBP80 payable once we start to manufacturer the PCB's.
If we have say 20 PFM'ers interested then I'll launch the project and spend an hour or 2 designing the PCB each night.