Currently I have my desktop audio set up, kinda maker style. it's a collection of parts, hooked together. A PCM2707 USB DAC, a classic 47 headphone amp and a bunch of 3.5mm Y splitters etc.
I would like to bring it all together into one box and put a few extra inputs onto it. I was putting it off as USB Dacs tend to be SMD only. I'm all ready about to bite that off and chew it for something else, so I can't use it as a blocker anymore.
So here would be what I would be after building and I would love your suggestions and input on choosing components. Note I am not an audiophool. I will be happy with 44.1 or 48khz output and 192 to 256 encoded data.
Inputs:
* USB DAC input
* Aux Input 3.5mm jack/RCA phono (these can on the same input)
* Bluetooth input
Processing:
Pre-amp, Gain booster with gain control - I'm tired of not having that little bit of extra gain from some quiet sources.
Outputs:
* Headphone amp w/ single 3.5mm jack output
* RCA/3.5mm x2
Starting with the DAC, is there much difference between the various Burr Brown/TI PCM270* DACs? Are the TDA chips any different? I'm assuming the datasheet typical application circuit would suffice? The headphone amp and pre-amp I can just copy the 47 Amplifier schematic but I might need to work out the impedance between them so I don't just lose all that gain. I might also need to check the current limiting on the main headphone amp and pair up two op amps on the output, though I think the 47 already does this.
On the multiple outputs, should I bother with unity gain op amps to balance the impedance or leave it as it? The 3.5mm jack/RCA will be output from the pre-amp stage.
The multiple inputs. Is it possible to have them duplex in that they are all active at the same time? Maybe with a mute toggle or gain control on each instead of a mutually exclusive selector? I suppose this could be done on the pre-amp, in a stereo pair of opamps on each input with a gain control on each input rather than a single on the output.
Finally, am I mad attempting this or should I consider an off the shelf solution that meets most of my needs such as some of the micro stacking components?