As I write this, I’m enjoying some Boston piped through the Robusto Amp. This was a pretty simple, yet satisfying build.

Robusto Assembly

The Verdict

With the bypass switch, I can compare the amp’s sound to the source. So, how does it sound?

  • With crap earbuds, there’s no difference.
  • With slightly better headphones, it sounds a bit “fuller” with the amp, maybe.

Overall, the difference is pretty minor (if it exists at all). I need to try two things: Line level input and higher impedance headphones. Even my good headphones are fairly low impedance.

Lessons Learned

  • The polarity protection diode payed off. While messing with the power supply, I reversed the polarity at least once.
  • I’m not so good on perf boards. Next time, I think I’ll spend a little more time up front laying things out. Also, I think I’ll try not using the component leads as traces, this makes it really hard to get them off the board if need be.
  • Don’t underestimate the time the enclosure fitting and final build will take. Granted, I’m pretty slow, and I don’t have much of a workshop, but this is a big part of the project. Where putting together a simple circuit on a breadboard is fast, fitting everything and soldering the final circuit can take an order of magnitude longer (for me anyway).

I spent a good portion of yesterday doing the final assembly on the headphone amp. All I had left this morning was to wire up tube and pop the top on. I plugged in the power and…

In the words of Isiah Whitlock Jr.: Sheeeeit! The LED was flashing, it’s not supposed to flash.

After a bit of poking around with the meter, I found the problem: I wired the LM317 regulators improperly. The output was shorted to ground. I carefully disassembled enough to get to the bottom of the circuit board and rerouted a few things. Once the LM317 was wired up correctly, it worked fine. I’m a bit surprised that the components stood up to such abuse.

Here’s the final product playing some classic rock:

Robusto Amp

Dave Rupert has some thoughts on the current state of the mobile app business in Addiction, the Mobile Currency. He offers a good analysis of where we are, and I agree with his conclusions:

In the wake of recent events I’d encourage those of us who build hypertext to have discussions about how you measure success. Are all of your KPIs attention-based? Are you driving addiction? Are you comfortable with the repercussions?

On a personal level, I’d encourage you to vote with your dollars and help create alternatives for attention- and addiction-based models of monetization. Subscribe to a newspaper. Fund a Patreon. Seek trustworthy sources.

Amp Front, with Jack

Yesterday was a productive day on the amp front. I made a little progress mounting components on the front panel. I also made a lot of progress with the electronics.

With everything wired up, albeit temporarily, I was happy when I saw the tube glow for the first time, and even happier when I ran some music through it. The amp sounds great. It has a brightness that others have noted, it’s the sort of profile that goes well with the warm sound of first track I played through it (What if We All Stopped Paying Taxes – Sharon Jones & The Dap Kings).

It’s not perfect. There is a low level hiss, noticeable only when there is no sound. I’ll have to see what I can do to get rid of that. It also picks up some RFI if something like an iPhone is within a foot of the circuitry.

Now I need to work on getting it cleaned up and in the enclosure so the guts aren’t splayed out on my desk.

Amazon GO is a retail concept that promises no checkout lines. Awesome!

I’m a bit surprised that the friction-free shopping experience they show in the video is kicked off by scanning a QR code from one’s phone. It would be slick if they extended their “Just Walk Out technology” to provide a less cumbersome just walk in experience.

We’ll see this sort of experience beyond stores operated by Amazon. I’m sure someone at Amazon is already has a deck describing how to package this for retailers. It will be great, I just hope that people without smartphones, Amazon accounts and credit cards can take part in this experience as well.

via NY Times