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

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: