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freeDSP Aurora-based USB 8-channel DSP/DAC/Preamp/Amp Build (in progress)

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#1
Build thread for my Aurora-based (almost) "everything" box. This will contain, at the very least, the following devices:

- freeDSP Aurora
- Mean Well RPS-30-7.5
- (2x) TPA3255EVM
- (TBD) (2x) JLE TICore260BTL
- Connex SMPS800RS

The intended use is for the Aurora to act as a USB sound card in my PC so that I can feed a stereo 4-way monitor setup.
 
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Thread Starter #2
The chassis for this build is of a clamshell style, comprised of two Fat Daddio 16"x12"x3" anodized aluminum rectangular cake pans. Since the material is aluminum and not too thick, the casework is relatively pleasant, though I must admit that the sides can distort as the aluminum is not particularly strong. In any case, I don't regret going down this route... at least, not yet.

First photo (IMG_9823) shows some of the layout work. At this point I had already mounted the power entry module and two power switches (1 for the Aurora power supply and 1 for the amp power supply). Those went pretty easily with a Dremel with abrasive cutting disc and a rectangular file. As for what's actually in the photo, I CADed the mounting hole layouts for the PCBs, printed them onto paper, and taped them to the pan so that I could punch the centers. Here is where I realized that my printer is not particularly accurate; on a ~140 mm span (I think lengthwise on the paper) the printed center-to-center distance is about 0.5-0.75 mm longer than what drawing calls for. Good thing I checked before I ended up with useless holes! My first solution was to score the paper with my digital calipers fixed to the correct distances, but eventually I just resorted to laying the PCB on the paper and then tracing out the insides of the mounting holes using a mechanical pencil. This actually worked surprisingly well, so much so that in the future I'll probably do away with the CAD & paper.

Second photo (IMG_9824) shows the marks from a Flexbar optical center punch. Love this thing. Not quite perfect (mainly an ergonomics thing) but it definitely makes quick work of punching accurate centers. One of the optical sight guides they provide with the unit has a sighting circle that pretty much lined up perfectly with the pencil-traced circles I drew beforehand, so if I had to guess, the accuracy of the punch marks is probably better than +/- 0.2 mm assuming perfect "centricity" on the included Flexbar optics and center punches.

Third photo (IMG_9826) shows the PCBs in place. I was expecting everything to fall into place, but it's still a relief when it actually does. Any guesses as to what the drawer pull and the as-yet-unused 1/4" bolts around the perimeter are for?

The amp modules will go into the other cake pan (not shown in any of these photos)
 

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Thread Starter #3
Pretty lights! Managed to finish off the GLB board and wire up all the power. Applied power for the first time and updated the firmware on the Aurora to the latest. Not liking the sound from the fan on the SMPS800RS, will probably swap that out to a quiet 80/92 mm PC case fan.

Not really looking forward to doing the wiring on 8 balanced outputs but it's got to be done. Will be starting the casework for the TPA3255EVMs soon.
 

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Thread Starter #4
Actually, before I start the casework for the TPA3255EVM modules I need to replace the analog input headers. Amongst other very-questionable decisions made by TI on this unit, the pins on the analog input headers are tin-plated; they are actually the only ones on the board that aren't plated in gold. So, I'm going to do that as well as replace the bulk caps with much smaller ones. Since I'm powering a bunch of modules from the SMPS800RS which has a manufacturer-recommended limit on load capacitance < 10 mF, I'm going to replace the stock 2x4700 uF caps on each module with 2x1000 uF 200 V. The higher voltage forces a bigger cap size which allows for higher ripple current rating.
 

abdo123

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#5
What an interesting project!

Did you make a list of materials (or is there one available) because i might just make one for myself!
 
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Thread Starter #6
What an interesting project!

Did you make a list of materials (or is there one available) because i might just make one for myself!
Thanks!

I will provide a BOM once all the parts/materials are locked in. Alternately, if there are specific questions you have I'm happy to help at any point.

It also depends on what devices you want to use, i.e. follow what I did exactly, or go with different amps etc.
 
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Thread Starter #8
Nice work!

Have you considered this kind of USB surface Mount connectors? For cable strain reasons I always prefer connectors to cable + rubber gaskets.

Keep us informed about the SQ!
Yes, but I couldn't find a supplier of it that I could trust, and also I wanted to minimize the number of USB connections so that the connection would be as reliable as possible. Having said that, if I had one of those cable assemblies available that looked like it was made well, I definitely wouldn't hesitate to use it (if I were to do this again).

Never had an issue with cable glands with proper rubber inserts, though. Many connectors use cable glands for stress relief anyway.
 
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Thread Starter #10
Really cool project
Thanks!

There are two reasons I started this: 1) I wanted an active multi-channel monitor setup that used my PC as a source and had DSP (obviously), decent 8-channel DAC, plus a relatively-easy-to-implement GOOD volume control, and 2) my existing setup has a really annoying ground loop that is too difficult to figure out (or that I'm too lazy to figure out... you decide). miniDSP is almost there, but doesn'tt quite tick enough boxes for this.

Doing a good volume control for 6 or 8 channels at a time is not trivial. VCAs aren't very high-fidelity, custom PCBs with relay-based resistor networks are labour-intensive, the learning curve (for me) with ICs like the PGA4311/CS3318 is too steep and still fairly labour-intensive, etc. The Aurora does it all and is very inexpensive comparatively.
 
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Thread Starter #11
FYI - the analog IO headers on the Aurora board have tin-plated posts as well (sigh), at least on mine. Anyone using the analog IOs on it, again assuming they get tin-plated posts, should be careful to use tin-plated female contacts on the cable header connectors, and preferably those with high-force contacts. Gold-to-tin contact interfaces are to be avoided due to propensity for excessive tin oxide build-up on the gold contact side, and tin-to-tin contact interfaces benefit from high contact forces so as to encourage breaking through the oxide layer.

ALSO, don't use high-force contacts in a full 24- or 26- position wire connector. That would require an extreme amount of force during insertion or removal. Break up the connection into chunks... I plan on using 6-position wire connectors (the ribbon cable shown in the photos above is only a temporary setup).
 
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Thread Starter #12
Replaced the analog input headers with ones having gold-plated posts. Job went quite a bit tougher than I expected, mainly owing to the fact that the solder pads on the TPA3255EVM are fricking tiny, and also that the thermal reliefs on the ground pads don't do much to relieve the massive heat suckout. To their credit, though, the PCBs held up quite well to way too many heat cycles on those pads without any real damage (solder mask got marked up since my iron tip was too fat).

Didn't have enough time to do the bulk caps but will get to that in the next few days.
 
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Thread Starter #13
Small update - have physically removed the bulk caps from the TPA3255EVM boards, leaving just the remnants of the pins to desolder. I had previously tried to desolder these using two soldering irons at the same time, but the PCB would just not let the pins get hot enough to truly melt the solder.

1_contents_removed_1.jpg 2_contents_removed_2.jpg 3_cap_base_removed.jpg 4_ready_to_desolder.jpg
 
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#14
Wow, interesting project - keeping an eye on this. I'm in the planning phase of making a fully active tower system, and have been beating my head over what DSP to use, because I'm planning on making multiple DSP boxes which needs to be "orchestrated". It is not fun to configure (at least) 6 DSP "client" boards one by one...
 

somebodyelse

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#17
It doesn't look like it unless you can find one on the used market, or source the components and assemble one yourself.
 
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