The plan with this headphone amp is to build it on a breadboard first. Partly to make sure it works, and partly because I’m still hesitant to etch my own circuit board.
Since the tube wasn’t going to fit on the breadboard, I was looking for something to attach it to, temporarily, so it won’t flop around. I found a cigar box in my small junk collection, which I think will do nicely. I mounted the tube socket on the cover and soldered in some hook up wire.
Even though it is meant to be temporary, this little cigar box could function as a permanent enclosure. It will need some ventilation holes though.
The tubes for the headphone amp were delivered today. The rest of the parts should be here this week. It looks like I may be working on this sooner than I thought.
Citibike is getting some pressure to expand to low-income neighborhoods. However, Motivate, the company that operates Citibike, can’t do that sort of expansion without some public funding, and the transportation commissioner seems to agree. I think this could be money well spent.
There are a couple success stories in the article linked above. For example, the woman that rides Citibike so often, each trip is about 9¢! That’s almost cheaper than walking.
I wanted to use a Raspberry Pi as an information display. To do this, I wanted a browser to open a page full-screen on boot. I thought this would be relatively easy, but I ended up spending some time troubleshooting. There are many, many pages out there describing how to do this, but some of the information is out of date.
Raspberry Pi Kiosk Screen Tutorial was very useful, although, I used the Midori browser instead of Chromium. Substituting “midori” for “chomium” seemed to work fine for this tutorial.
As for the autostart file, note that you might have several of these on your pi, I suggest checking to see if you have a user config file, that one will take priority over any of the others (including those listed in the tutorial above). Mine is at /home/pi/.config/lxsession/LXDE-pi/autostart.
The web page I’m running relies on local storage, and it seems that Midori has that option disabled by default. I enabled it, and it worked great when I launched Midori in the desktop environment, but the page failed to load when launched from the command line. After some poking around, I saw that the Privacy tab wasn’t in Midori’s preferences when launched from the command line. I “fixed” that by making sure pi user’s config was getting loaded.
The line in my autostart file that opens the browser looks something like this (note the -c flag):
@midori -c /home/pi/.config/midori -e Fullscreen -a http://[URL]
With that, it worked great!
My electronics projects have been non-existent for almost two years now. I’m going to kick things off again by building a headphone tube amplifier. This comes after months of prodding from Carl followed by a conversation where he basically said my creative output has dwindled to zero. I agreed, so here we are, building a little tube amp. Rather than waiting until the end to do a write up, I’m going to post as I go. Now, on to the build.
DIY headphone amps are far from untrodden territory. There are many designs out there, and several places to get help. After a little bit of research I considered these hybrid amp designs:
I decided on the NP-100v12 due to its low part count and availability of the 12AU7 tube. The photo above shows a finished build from Rogers Gomez. I think this will give me a good introduction to tubes and amps. If I had a bit more experience, I’d probably lean towards one of the Millett Max amps.
Stay tuned for more…
Photo from diyaudioprojects.com