Power12: The Mini6 Again, But Better

Lid Open

I’m back with another amplifier project, but this time it’s kinda like a remake instead of a completely new amp. The story behind this project started 4 days after I completed the Mini6.

While I was drilling the holes for the jacks on the Mini6, I accidentally put too much pressure on the acrylic enclosure and it cracked, it was very small crack, practically impossible to see, between the two RCA jacks on the front, but after using it for a while and noticing how the crack would open a little bit every time I plugged something in, I decided to fix it using super glue (facepalm) and while I was using the glue I didn’t notice that one small drop fell in the PCB. I put everything back together and tested, it sounded horrible and when I looked inside I could see the stain of the glue which was destroying the sensitive part of the circuit. So in a moment of rage I decided to throw the whole amp in the trash and design a better one and put it in a better enclosure. So that’s how the Power12 was born.

Schematic

The first thing I did to the original design was add a Zobel network to increase the stability of the amplifier. The other modification I did was the addition of a active load in the gain stage. Sadly when I was designing it I forgot to add another active load for the differential pair, but this will be fixed in the next revision of the board (I’ll also add a SIM).

No heatsinks

Populating the board was a pretty straight forward process since there aren’t a lot of components to be placed and as usual the most difficult port was soldering the spade terminals to the ground plane.

Enclosure

This time I decided to use a very nice extruded aluminium enclosure that I found on AliExpress. I was a bit skeptical at first about the quality of the enclosures, but when they arrived I was surprised how beautiful they were, and the quality of the extrusion was really good. The seller was great, emailed me to ask about the customs, shipped extremely fast, and packed everything extremely well to make sure nothing would scratch the very fragile black paint of the case and the panels.

Since I decided to use a aluminium enclosure, the best combination would be a very minimalist design, so the only thing in the front panel is the power switch. This decision gave me the idea to place the power LED on the back, giving it a really cool look when it’s powered on.

Back panel

Drilling the holes for the 2.1mm power connectors was a pain in the ass since I didn’t have a drill bit that was bigger than 8mm, so I was forced to use the “wiggle” technique to make the holes bigger and because of that the drill bit escaped the hole a couple of times and damaged a bit of the back plate, but since it’s on the back no one will ever see my mistakes.

THD Plot

The distortion figures are not the best you’ve probably seen (it’ll be a lot better when I add the second active load in Rev B), but it’s low enough that you won’t be able to notice it. The plot was created using a script I’ve created called plot_thd.py, running this SPICE circuit. Sadly I don’t have the equipment to measure the real figures, but I’m planing to buy a Keithley 2015 next month.

Temperature Profile

One thing that I actually was able to measure was the temperature profile of the amplifier, and as you can see it runs pretty cool with those FA-T220-38E heatsinks. Those figures were measured with the lid closed and with the amplifier right at the point of clipping with a 1kHz sine wave into a 8 ohm load. I’ve used my Agilent U1242B multimeter in conjunction with a program I wrote called dmmlog to grab the data, then plotcsv to generate the graph you see. Sadly I forgot to take pictures of the test setup.

If you want to see all the pictures of the project this Imgur album contains all of them. If you want to have access to all of the files related to this project check out the GitHub repo, and if you want to discuss it the best place to go would be the diyAudio thread.

My Raspberry Pi Post-Mortem

This might be the worst day of this current year. As you might already know yesterday, after 4 months of agony, I finally received my Raspberry Pi. It cheered me up a lot, since in the same day my old Galaxy S bricked. Today the perfect chemical reaction occurred. All the excitement and expectation converted entirely (maybe multiplied) into a strange mix of frustration, sadness, and anger. My Raspberry Pi arrived dead.

After 4 long months of wait, ~20 items on a TODO list, 3 projects, 2 VMs, ~50 tweets, and 3 articles, it all came to a sad end. Today my friend borrowed me his spare USB keyboard so I could turn ON an configure my Raspberry Pi for the first time. While it was booting I had one of the most awesome experiences ever: I’ve watched the original Linux boot, with a logo on the left corner and all those awesome lines blazing through the screen, just like in 2005 when I booted Linux for the first time on my extremely old IBM ThinkPad. After I saw those lines for the first time I decided I wanted to know more about how things were made, Linux got me into programming, and turned me into what I am today. It was a awesome moment to watch those lines again.

The first thing Raspbian did was show me a nice ncurses-based configuration tool. I started configuring it and suddenly “No Signal”. I looked at the Raspberry Pi and the only thing that showed me it was working was the Power LED, all the other LEDs (including the internet ones) turned OFF. I disconnected the power and tried booting it up again. This time it did the same thing, but a lot earlier.

I rushed to my computer to check if it was a known issue and if someone had a fix, many users had similar issues, but not the same, the suggestions were the same: Check the power source voltage and the SD Card. I’ve started by downloading the other distros and flashing them on different cards, without success on the Pi, I was still having the strange issue. Then I decided to get a multimeter to check the voltage of the board, when I checked the board voltage it was great, so it means it wasn’t the power source causing the issue. All I got was to acknowledge that I got a faulty unit.

I inserted the Raspberry Pi back into its case and gently stored it into the drawer were I put all the electronics that stopped working, which currently contains only my first laptop (that ThinkPad with Linux) and my Galaxy S. I care a lot about all my electronics, even after they are “dead”, that’s why I never sold, or trashed any of them, which means I almost have a museum here in my room, with all the devices I ever owned.

I’m curious to know what will be the next thing that will get me as excited as the Raspberry Pi did. Computers, they aren’t fun to play with anymore, and the Raspberry Pi changed this. The mobile world that always excited me, since the day I got my Palm, is no longer that exciting. So what’s next?

I don’t think I’ll be buying another Raspberry Pi, probably not. All the excitement extinguished today.

Updates:

If it’s Good I Don’t Care Which License it Uses

Today I could finally watch the Stallman’s interview on The Linux Action Show, and their second video about it, and I couldn’t agree more with Bryan, so I thought about writing an article about it since most of the responses I saw were just a lot of crap thrown at a person that wants to make a living out of software development.

Stallman has a great dream that software should be “free”, but I think that the developer must also have the freedom to choose if they want to charge or not for their software. Free software is great, but if a developer wants to make a living out of their software, which means be dedicated full-time and not have another job, it’s almost impossible if you only make free software, even if you accept donations they won’t be good enough to make a living. Which means you’ll have to charge for some of your software.

When I’m going to get any kind of software the first thing that I look is at the description, what it does and what it doesn’t, then I look at the screenshots. If the software is considered good (in my opinion of good) I’ll download, if it’s free, or buy, if it’s paid. The developer has the freedom to choose the price of their software and I respect that, if the developer thinks that his app is worth $10 and I think it’s worth too, I’ll surely buy it.

Bryan and Chris also talk about the proliferation of the “App Stores” as a bit of a bad thing. Of course it has it’s cons, but they have a huge pro which is how easily it makes for users to discover and get software. This is good for the user, that will be able to get more software to fit his needs, and is good for the developer which will get more downloads/revenue.

Let’s take me as an example. I’m a student which is very thankful to my parents for supporting me to study and have some time to develop software for fun. That’s why I build software that I want/need to use the best examples (and the ones I’m mostly proud for) are build.prop Editor and stream.json, these are all licensed under the GPLv3, but I’m going to start reworking (long story, worked for 1 month to start this project, all was almost ready and a lot of bugs on bbUI.js made me very depressed and leading to my rage quit from BlackBerry development) and it will be a $0.99 app for iOS, Android, and maybe BlackBerry. My decision to charge for this app is just because of the time I’ve invested and will invest on it.

Free software is a great thing, but the blind way that Stallman looks at this scene is just mind blowing. If he really wants that every company that develops proprietary software fails he is just going to kill his own idea because most of the big free software projects are possible because huge companies that earn money from proprietary software can pay for employees to contribute to these free projects.

Stallman also said that he wouldn’t use/recommend the Raspberry Pi just because of one single proprietary part of it (which is probably the GPU). This, and the discussion about child’s food that he had with Bryan, showed how he cannot think about practical implementations of his ideals of freedom. Projects like the Raspberry Pi are the things that are currently keeping my interesting on programming, since the programming scene is so saturated that everything I think might be a cool week pet project never comes out of the paper I’ve sketched, because there’s already a well known and successful project which does exactly what I wanted and more.

What are your thoughts about my opinion? Want to troll? Agree? Leave a comment and I’ll love (or not) to read it.

PS: This post was written using proprietary hardware on a Apple MacBook Pro 17” (2010 model), running a proprietary OS called Mac OS X, using a proprietary word processing software called iA Writer.