I got all hot and bothered with skrodahl's great Amplifier/RPi build, (http://www.runeaudio.com/forum/tpa3116-runeaudio-project-t319.html)and wanted to do something similar. As it were, my board was just sitting out in the open. There was a temptation to leave it that way, I dig the geek factor, but it does look a little off compared to the rest of my system.
DSC_1686b.JPG (235.43 KiB) Viewed 3024 times
This is my layout, very similar to skrodahl's at http://www.runeaudio.com/forum/tpa3116-runeaudio-project-t319-50.html. This is extruded aluminum, and didn't have a top/bottom section, which would have made it easier to build. As is was, I mounted everything on a spare chunk of Lexan that was cut to size. It just slides in and is pinched firmly in place when the box ends are screwed on. Cord doesn't match; it came off the scrap pile too.
The power supply is a 3A version, and only just fit under the hood. I wanted the room to grow, just in case. The little silver box is a EMI filter, which I am hoping (haven't plugged it in yet) helps with the hash coming off the switching power supply. When I had just a wall wart running my board, there was a very audible difference between having the wart plugged into the wall, or directly into the power output on my pre-amp. The latter was unbearable it was so full of switching hiss. And this is just a difference of 18 inches worth of mains power distance. I should point out that this was before I had the HiFiBerry DAC+ installed. I have been using line signal directly from the Pi headphone jack. Not a good situation anyways, but the noticeable noise difference in power supply hookup makes me think the switching hash has been backfeeding. Hopefully the filter will knock most of that down.
DSC_1688b.JPG (210.38 KiB) Viewed 3022 times
The mains power comes in on simple two conductor lamp wire, 18awg. I used this rather than a grounded IEC connector so I can plug it into the switched power on my pre-amp. Ungrounded always makes me a little leery, though it would have gotten a fuse anyways. When I build for other people I use grounded, fused, connectors. But this is my rig, and it needed to fit my system. White wire makes me grind my teeth a little, but I didn't want to scrap a good box fan for black wire and plug.
The on-board wiring is 18awg solid copper; it's way way easier to work than stranded. It bends and *stays!* That way I can keep the 5v power away from the mains a bit; anything to reduce noise! (It's a compulsion of mine.)
I really wanted to be able to pop USB cards in and out easily; it works really well for the size of my music library, and this will make it easy to update the library when I buy more music. Also if I end up putting in a wireless dongle, etc etc. I like the RPi B+ for the four USB ports. Cheap flash drives go a long ways. Drilled everything out, and then took a triangular file to get the square holes. I have about four blisters at the rate of one blister/hour. Filing holes to the right dimensions was far and away the longest part of the job. Not exactly millwork, but it will do. You can see a few places where I got going too fast, popped the file out of the hole and gouged the anodizing. Again, there is a 1:1 ratio of gouges to curse words. I gotta say, though, with the force I was putting into it, this anodizing held up remarkably well. Others I've worked with haven't been as forgiving.
DSC_1692.JPG (214.9 KiB) Viewed 3021 times
Decent little chassis mount RCA jacks that soldered up well and were leftover from another project.
I didn't have a banana for scale, so a tomato, onion, and knob of ginger will have to do.
Pretty plain, all told. I had grand plans for carving the RuneAudio symbol into the faceplate, casting resin into it, and then backlighting it with blue LEDs. With the EMI filter, I really didn't have enough space to cram anything else in. (Well, I might glue a lego man in there somewhere.) Maybe I'll go back and try again in the future. Everything is mounted to the back plate, and the end plates are bought separately, so I could have a few do-overs and not have to replace the whole box. In the meantime I'll probably just paint it on the front. I promise photos if I ever get around to that.
DSC_1694.JPG (206.66 KiB) Viewed 3018 times
I played with casting clear resin into a shape in aluminum, painting it, and then backlighting it. It makes for a *very* sweet look, if you ever want to try it. The front plate looks flat, normal, nothing, but when you turn it on, the backlighting casts a sharp, lit image through the paint. I had a hard time with A) getting the paint to lay flat along the seams between aluminum and resin B) getting the resin casting flat enough that scratch marks didn't show through and C) finding a flat black paint that light could show through. Lighter color paints work fine, but even thin coats of flat black obliterated any light. If anyone has ideas for workarounds, please let me know.
The plug on this thing is non-polar, because that's what I had around, and that's the only thing that will plug into my preamp. While some electronics are not particular, a switched power supply seems like it could be, if the signal isn't rectified before the electrolytics. This power supply has line and neutral (and ground) so I am going to assume for the time being that it should be hooked up as such. I spent some time with the DMM double and triple checking the hot/neutral lines on the pre-amp to make sure this neat little rig doesn't end in smoke. (It's *REALLY* hard to get the smoke back in. )
I've forgotten; I didn't include a switch, because this will be powered from the 'switched' power on my pre-amp anyways. So no need there. I was thinking, it would be pretty cool to build a 'touch' switch (like the kind commonly used for turning on lamps) for one of these, especially along with the above bit about casted resin. I never got around to it, but there is plenty of space in this chassis to put in both a touch switch, either a DIY one, or an off the shelf lamp retrofit switch, so long as there is space. I don't know if you would need a relay to handle the amount of current passed but I think an off the shelf kind would be okay; filament lightbulbs take up way more current than the Pi boards. If you were building a tube amp, it probably *would* require a relay. Also, I don't know if the hash created by the power supply would wreak havoc on the capacitive sensing portion of the switch. If so, maybe the sensitivity could be decreased? I haven't found much info on this yet; another project for another day.
The box didn't come with screws, which is weird, but had some spare cap bolts (tiny) sitting around that worked and look pretty decent. The QR code is courtesy of Stwert, who foresaw a way to make this easier for visitors. I have lots of guests through my home, and I hope the simple tented paper with code and static IP will make it easier for them to navigate into and enjoy the sound system.
Well, that's been my project for the last few days. Rune 0.3 Beta drops in a few hours and I am excited to plug the thing in. I will, of course, post.
Thank you all! The good folks at RuneAudio, and all of you with great, *inspiring* ideas that make me want to get out the soldering iron.
Hi Fishstix, and congrats with a very nice build. You should put up some pictures (yes, there can never be enough pictures) of your resin cast, so it's easier to visualize what you're doing. Could the same thing be done with plexiglass and overhead projector foil? Plexiglass lit from the sides gives a very nice effect as well.