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blogroll
Mon, 15 May 2006
business is good. business is booming
I've been doing my best impression of a shiftless layabout for the past week—they comp'ed us a week of vacation after tapeout to thank us for all the overtime we put in, so I've been catching up on life—but I did manage to do a couple interesting things.
First, embarassingly enough, Mike convinced me to start playing City of Villains (remember last summer and City of Heroes? I sure don't), but I've only played a small bit of it thus far. It does seem damn cool, and I'm intrigued by the way they've subtly changed the hero archetypes to make altogether different-feeling characters that are still very familiar in their powers. May, you gonna start playing with me now?
Second, I decided that I'm done "missing out" on that "magic vacuum tube sound," so I've designed and am now in the process of building the amplifier you see to your right. whamp (Wahby's headphone amplifier) is the best name I've come up with thus far, but please feel free to suggest others. Note that a couple years designing circuits for ICs has rendered me completely incapable of anything approaching simplicity. Also, the extent to which an op-amp with a non-inverting second gain stage is a pain in the ass to compensate is left as an exercise to the reader (and then note my solution, a pretty cute one if I do say so myself).
For those of you about to protest, "but that's mostly solid-state!" you're absolutely right, but consider that the majority of the amplification is coming from the vacuum tubes, and thus the majority of the audible distortion (which is what really creates the "magic"). Put another way: input refer all the distortion, and all but the distortion from the 12AX7s is attenuated by the gain of the input diff pair. Thus, the "sound" of the amplifier will be mostly dictated by the input pair. This claim is supported by my simulation results, which show that most of the harmonic distortion is in the even-order overtones, the characteristic distortion profile of a vacuum tube amplifier. By the way, I expect that at reasonable volumes I'll get less than .002% THD into my 250 Ohm beyerdynamic DT-880s, which may actually mean that I've designed it so well that it doesn't sound like a glass amp after all. At least it'll look cool...
Edit: updated the schematic to the latest version, which now uses a slightly different compensation scheme and some snazzier output transistors.
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