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keves

Attempt at evaluating PCM4104
« on: November 27, 2016, 05:48:15 PM »
Hello,

As part of a MIDI controller/mixer I am trying to build, I want to use the PCM4104 4 channel DAC (http://www.ti.com/product/PCM4104). I am pretty sure I have the USB->I2S stuff figured out on the microcontroller I am using, and before designing the final board I want to hook up the evaluation kit to a PCM4104 and play with it for a bit. I know there is a $200 evaluation kit, but I figured I would like to make my own as a step towards the final hardware design.
I have very limited analog design experience, so I simply copied the data-sheet/evaluation kit reference design, and kind of half-assed the power supplies. My goal is to get the thing working for now, and later worry about performance optimizations.
I will be feeding this board +/-12v DC regulated by a pair of LM317/LM337 cheap modules I have around, and +9v DC from a lab PSU.

If anyone has the time, can you please take a look for any obvious mistakes/potential issues?
Note that this design will be completely open-source and I will be providing both the Eagle files as well as software once there is something to show. To my understanding there are not a lot of DIY 4 channel MIDI controllers/mixers around there. If anyone's curious the CPU will either be an STM32F4 variant or the new STM32F7.

Schematics are attached and PCB rendering is at http://imgur.com/a/uEM4I

Thanks!


Rochey

Re: Attempt at evaluating PCM4104
« Reply #1 on: November 27, 2016, 10:15:49 PM »
Your caps on the references you have are a little small. pop on a footprint that lets you put a 2.2uF cap too.

Your design on your output stages have a 2K between the differential out. That is pretty low. You're assuming that the PCM4104 can drive a 1KOhm to mid-rail. I've looked at the EVM schem, and it does the same... but I'd still prefer a higher value.

One big ground is good - your system partitioning is good. There shouldn't be any digital return currents going around your sensitive analog outs, although I'd move your EN-DAC and DAC-VCC jumper nearer to the output connectors, so that they don't run over your analog outputs on the top of the board. Consider moving the DAC 1117 regulator to the middle of the board, and the connector near to it. It's okay to have connectors mid board yaknow :) My moving that regulator to the middle of the board, routing your VOUT's for channel 2 and 3 will be much less likely to be impacted by the power rail switching all over the place.

That's all I have for now. Good luck.

/R

Expat Audio Home: http://www.expataudio.com

keves

Re: Attempt at evaluating PCM4104
« Reply #2 on: November 28, 2016, 12:47:04 AM »
Thanks for taking the time to look at this!
I'll try moving the things around like you suggested. With regards to the 2K between the differential out - notice that it is not populated (There's a note about that on the  EVM schematics). Why is it there at all?

deva

Re: Attempt at evaluating PCM4104
« Reply #3 on: November 28, 2016, 01:15:32 PM »
Maybe I'll look really stupid for this but...

Is it just me, or are the jacks facing the wrong way from the board edge?

keves

Re: Attempt at evaluating PCM4104
« Reply #4 on: November 28, 2016, 01:39:40 PM »
Haha, you might be right :)
It doesn't really matter since I'll be hand assembling the through-hole parts, but yes I am not sure I placed them in the right orientation  ::)

mattamatta

Re: Attempt at evaluating PCM4104
« Reply #5 on: December 05, 2016, 02:39:23 PM »
You may want to verify the clearance of the jacks with the surrounding parts.  That rectangle on the left that says Neutrik (which will be on your right when you fix it) is probably a nub that sticks out as these jacks sometimes have, so be sure that it's not overly close to the IC leads or caps.  May want to consider the ability to get an iron in there for rework; if not, at least keep it in mind during assembly and do the ICs first if soldering by hand.

joaquins

Re: Attempt at evaluating PCM4104
« Reply #6 on: December 05, 2016, 07:07:32 PM »
You may want to verify the clearance of the jacks with the surrounding parts.  That rectangle on the left that says Neutrik (which will be on your right when you fix it) is probably a nub that sticks out as these jacks sometimes have, so be sure that it's not overly close to the IC leads or caps.  May want to consider the ability to get an iron in there for rework; if not, at least keep it in mind during assembly and do the ICs first if soldering by hand.

I'd load the jacks from the opposite side as the SMD parts and you could even get away having components under the jack, almost the whole stage would fit there reducing significantly the board size, if that's a concern.

JS
If I don't know how it works, I prefer don't turn it on.

keves

Re: Attempt at evaluating PCM4104
« Reply #7 on: December 24, 2016, 01:04:46 AM »
Excellent ideas, thank you! :)