![]() The Pro has basically the same output tube complement as the EarMax, but can provide higher current output into low impedance headphones. ![]() Since the publication of that article over a year ago, there have been several inquiries regarding the possible topology of the EarMax Pro. This previous version of this article was a summary of the information collected from the Sound Practices archives and from the HeadWize forums about the original Morgan Jones circuit. I contacted Chiu for more information, but apparently he no longer remembers many specifics about it. I scoured the Sound Practices archives, downloading year after year of digests, and finally found a posting by Johannes Chiu, who described enthusiastically his DIY work on this design. Given all the interest in the audiophile community about the EarMax, I thought that surely someone, somewhere, must have tried to build it. Lance Dow, who knew Morgan Jones personally, had posted the schematic in that newsgroup way back in 1996. While doing research on the internet, I came upon a reference to the Jones design in an archive for the Sound Practices mailing list. I once again put the schematic away, hoping later to find a DIYer who could give construction details. ![]() Jones had created the circuit as an academic exercise, but had not actually built it. That is, the schematic was not of the true EarMax, but was derived from the published specifications of the EarMax (e.g., 3 tubes, the power supply voltage, the input and output impedances). In the book, Jones described it as a reverse-engineered version of the EarMax. ![]() Months later, I saw the schematic again in a book called Valve Amplifiers (2nd ed.) by Morgan Jones. Since he had no more information about the design and had not built it, I filed it away to be referred to at a later date. The sender told me that it was supposed to be the schematic for a “clone” of the famous EarMax miniature headphone amplifier. Back in 1999, I received an email with an attached schematic of a tube amplifier. ![]()
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