If Sony were to come out with such a tube amplifier and docking station, I bet it would sell well in Japan and Europe, as small, cute, and excellent are valued. Here, in the USA, however, Headroom could probably only sell a few hundred units, as most music lovers to whom I have mentioned this project have responded with, “Why bother? The player comes with a headphone jack.” (Maybe the fault lies with the same Midwestern outlook that allows boring cars to be made decade after decade. Don’t you love the new ads from the big two: “Our cars used to be much worse.” Imagine if Detroit wised up and did what Japanese car makers do: had their cars built in Michigan only after having been designed in San Diego. I went into a high-end audio store in Ann Arbor MI and looked around. Not a single tube to be found. I ask where the tube gear was hiding and the owner moaned and asked, “You’re not from California are you? Californians always ask that.”)

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      A reader wrote:

     Thanks for the best resource in audio design. I can’t wait for new material on your website. (I wish you still published everything in a PDF format, but I can see where the blog style must be easier to create.) I have learned so much in the last three years, compared to the twenty years I spent reading Audio Amateur and other magazines. I just wanted to tell you that I built a headphone amplifier for my Sennheiser HD600s based on your Broskie cathode follower circuit. The headphone amplifier accepts a balanced input from my CD player which has an XLR output and it delivers the best sound I have heard from my headphones yet, clear, effortless and naturally smooth sounding. A friend of mine who is a musician, recording engineer and a record producer gave the amplifier and headphones a listen and he wanted to buy it from me right then on the spot. Sorry, no chance, was my answer. This was only my second tube project (I’ve built about 10 solid-state projects over the years) and I plan on building a single-ended hybrid amplifier based on one your circuits from the simple amplifier article. Thanks again.

Bill G.


     I didn’t think the circuit would work all that well into a 300-ohm load, so I modeled Bill’s implementation in Spice. WOW. It sure does measure well. The next step is actually to build the circuit and give it a listen with my HD580s.

     Of course, not every CD player has an XLR output, which limits this circuit’s appeal as a standalone headphone  amplifier. But adding a grounded-cathode amplifier and a split-load phase splitter would be easy enough. As the output stage already holds a feedback loop, I don’t see the point of adding a global feedback loop, except for when driving 30-ohm headphones, so a switched feedback arrangement would be a good idea.   

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     So is this the circuit for the docking station? Maybe. But I still admire the simplicity and excellent performance of the grounded-cathode amplifier cascading into an optimal White cathode follower.  The circuit results in a predictable gain and output impedance and an excellent PSRR figure.