I think I need no make some of these little, magnetic PCB vises. They look like they’d be much less cumbersome for small parts than the vise I have now.
With the bypass switch, I can compare the amp’s sound to the source. So, how does it sound?
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.
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:
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.