Newbie wants to build all-in-one streaming unit


2013-01-22 5:46 pm
Hey all,

Long time listener, first time caller. I'm an attorney with an undergrad physics degree, so I've taken electronics classes, but never had to independently engineer anything (nor do I remember much of what I learned back then beyond the bare necessities). Am still playing around with CMoys and all that to get my basic sautering skillset up to par. So y'know. Noob.

I'd like to make an all-in-one streaming unit. I was thinking something like a raspberry pi (with raspyfi or squeezeplug) with a wireless USB dongle and an ODAC filling the USB ports, with the ODAC outputting to a three-way switch: speaker stage, headphone stage, and line-out. Speaker stage would be linked to a pair of Linkwitz Pluto clones: the ODAC line-out would go through a minidsp 2x4 balanced unit, then out at line level into faux-Plutos with small, prefab (i.e., not DIY) power amps in their bases. The headphone stage would go through a Meier crossfeed (lifting from the Corda Cross-1), then into an O2.

The main idea is to build something that checks all the boxes without breaking the bank, while allowing for some later upgrades (building the crossover and amplification for the Plutos to spec, for instance); something to tide me over for a while.

Being an EE ignoramus, I had a few questions and would appreciate any other guidance you all could offer:
1. Impedance into the crossover circuit. The original Corda Cross-1 had six-position bass and treble switches to account for input and output impedance. I seem to recall reading that the ODAC had an output impedance of about 40 Ohms, while the O2 has "Input impedance >= 10K" (source). I am not entirely sure what that last figure means (10 KOhms?), and am not sure quite how to account for it in the crossover design. I think I can pull out the resistors used for the appropriate switch positions (the Corda Cross-1 manual lays these out), but would appreciate any guidance you all have on that point.
2. I am really lost on how to power this thing. I'm fine with using up half a power strip to power discrete components when I'm clumsily breadboarding this monster, but after that I'd like to have everything running of a single plug. I apologize if this is overly ignorant, but is that a matter of good voltage regulators, independent power circuits for each component, some multi-rail power supply pcb, or something I've missed? Just trying to narrow the field of what I need to research.
3. Thoughts generally? I like the idea of taking all my functions and squeezing them into a single box. My collection is all digital at this point, so I have no need for fancy phono pre-amp stages or anything like that. I'm just not sure of the soundness of this plan from an engineering point of view (e.g., wifi dongle interfering with the internal electronics, the effect of having all these components in a tight space, etc.). I'm not looking for absolute electronic perfection, but I'm picky enough that I'd rather spend some time on the front end planning it out than overhauling it down the road.

Thanks for any input you may have!
Hi, I am currently building an amp that consists of ODAC, O2, OTL Tube Amp, 2x Linkwitz Crossfeed and Raspberry Pi with RaspBMC.

Unfortunately I am still waiting for my front- and backpanel from the housing. So i was nat able to connect the individual part and test them. But I'm already now thinking of a new HeadphoneAmp/Preamp with a built in Raspberry.
Currently I am getting the digital Audio from the USB-Port of the Raspberry which is then connected to the ODAC. The next step would be to direcli connect a DAC via I2S to the PINs on the board.

However to answer your questions :)
1. Amp/Cinch inputs usually are designed to have a 10kOhm input impedance. The Linkwitz -filter has a high-impedance Version that I would recommend. However wether you have exactly 10kOhm or more or even less does not really matter.
2. Just look on mouser or digikey for a 5V power supply. You will find nice finished boards for about 40$ or even less
I am also thinking about such a solution. In my specific case I want it to be as minimal as possible, so only connections for: wifi and AC in and speakers out.

Raspberry PI -> ESS9023 DAC -> Hypex Uc180

Raspberry PI -> ESS9018 DAC (Buffalo DAC) -> Hypex NCore

Things I've to consider:
- extract I2S from the Raspberry: this seems possible from the free spots near the GPIO, but also a driver update is necessary (I plan to use Squeezeplug)
- use the switched 3,3V or 5V from the Raspberry's GPIO to trigger the DAC and the power amps (the Hypex's have 12V trigger input).
- how do I arrange volume control (preferrably via the control app).