Transistorize!

100 2N5087 transistors, sorted by hFE.

In order to ensure that the left and right channels of the Millett Hybrid MAX headphone amp sound the same I’m trying to ensure that all parts used in each are balanced. So, I ordered 100 pieces of each of the 2N5087 and 2N5088 transistors. I was able to get four parts which consistently metered identically, so those are used in order to ensure that the current to the tubes is kept consistent. For the other twelve transistors I was able to get matched pairs (at least) and ensure that the values are the same for each ear. That should work out well.

This evening I also figured out the template for the rear panel, drilled it, ensured that the parts fit, then put it together. I’m pretty happy with how all the parts fit, although I did have to shorten the heatshrink on the phono connectors so that the wire could bend better. When I test fit the PCB and the rear panel everything fits nicely, although the wires will be a little cramped.

Since I placed all the matched transistors, new 1/4″ jack, and replacement tube sockets I’m now ready to wash the board and finish it up. If things go as planned I’ll have it working either tomorrow or friday. Hopefully it’ll sound good, although I imagine that won’t happen until the tubes are burned in and biased, I’ve selected the tubes I wish to use, and it’s all done.

I also have to make the front panel (should be easy), potentially cut the shaft of the potentiometer shorter to fit the knob (risky, not really easy), possibly drill some arrays of vent holes on the top, front, and rear panels (easy, if I drill them right), cut the tube holes, and finish assembly. There’s also deciding on the set of tubes to use, so I’ll probably run it without a top at work for a while, but I’m not sure yet… That’s all up in the air.

Oh! I should also really make a photo to iPod dock connector cable… Or maybe I’ll just buy a new dock and use a phono to 3.5mm cable… Hmm….