One of the most popular uses for the Raspberry Pi computer is turning it into a media player. Various operating systems and skins like XMBC and Kodi let you browse and play music and movies with relative ease, and dedicated music-player variations like Volumio and add-ons including HiFiBerry’s Pi-based boards have emerged. Now one group is taking it even further with a hybrid vacuum tube-amp add on for bringing warm, vintage analog tone to your Raspberry Pi.

The project, called the 503HTA, packs a single 12AU7 or 6922 tube and a solid-state IRL510 Mosfet circuit into a hybrid amplifier that mounts to 40-pin Raspberry Pi boards, including the Pi 2 and Pi 3. It includes a 24-bit DAC, a gain select switch, and a 3.5mm headphone jack. Putting out just 500mw, it’s designed to power headphones from 32–300 ohms, or act as a preamp for powered stereo and speaker systems. Just be careful when doing that to keep the gain switch at the lowest level to not burn out your amp.

503HTA rev2

Michael Kelly, creator of the 503HTA (which launched this week on Kickstarter) and owner/chief designer of Rhode Island-based Pi 2 Design, tells us they decided to embark on the project after an accidental literature encounter. “One of my engineers was looking in my library for something and came across my 1973 RCA Receiving Tube Manual,” he explains. “He asked what I knew about tubes and I bored him for about an hour regaling him of my days doing tube designs as a kid in the 60’s and 70’s. A few days later he asked ‘We’ve done a stereo DAC and surround sound output hat, why don’t we make a tube amp?’ At first I shuddered at the thought of using tubes again, but after looking into it I found a number of low-voltage tube designs that folks seemed to really like. Designs such as the Bravo V2 seemed easy to implement and improve upon based on suggestions in a number of community forums. Thus the 503HTA was born!”

Although this is the first vacuum-tube expansion board we’ve seen, it’s not the first Pi-based tube amp project. Tube Net Radio from German site doc-diy.net is one particularly interesting integration of a Raspberry Pi and a vintage tube-powered radio, allowing the project creator to listen to various online streaming services through the original circuitry.

As for the 503HTA’s sound, Kelly responds, “It sounds surprisingly good!  I say surprisingly because I was not a big fan of the tube sound in general, never mind one that runs at such a low voltage (for tubes).  But, it is very nice and listening to a wide variety of music I found it to be easy and not at all fatiguing.  I guess these are hallmarks of the classic ‘tube sound.'” 

The 503HTA Kickstarter campaign runs until June 6. A few $109 early-bird options are left; after that, the amp costs $149. It is expected to ship to backers between July and August 2016.

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