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Hackable media-streaming speaker does HiFi with tubes

Apr 23, 2014 — by Eric Brown 2,523 views

Tubecore’s “Duo” wireless media-streaming speaker embeds a Raspberry Pi or Udoo SBC, and features Bluetooth and WiFi, plus a 48v Class A analog-tube preamp.

At $649, discounted to $479 in the current pre-order phase, the Duo costs more than typical $50 to $200 wireless speakers. However, it’s also a full media player that can stream HD video to a TV, and can also pound out high quality uncompressed audio from multiple sources. Products ordered today will ship in July.

Tubecore Duo
(click images to enlarge)

The 18.5 x 9.4 x 8.5-inch device runs Linux on a Raspberry Pi SBC, or for $110 more, on a quad-core, Freescale i.MX6 based Udoo Quad, which also runs Android. Each SBC furnishes Bluetooth and WiFi streaming, as well as I/O made available at the rear of the system.

The Duo comes with a Raspberry Pi (left) or Udoo Quad SBC
(click image to enlarge)

The Duo stands out with its 48v Class A Preamp, which runs all audio through analog vacuum tubes to produce “rich bass, warm mids, and crystal clear highs,” according to Tubecore. The default preamp is an Electro-Harmonix ECC82/12AU7 with >100dB (20Hz to 20kHz) dynamic range and 10Hz to 20kHz (+0/-1dB) frequency response.

An April 18 Engadget story, which alerted us to the Duo, offered a few additional details on the preamp from Tubecore reps. According to the story, the preamp filters an incoming audio signal six times to remove any excess noise. Several pricier preamp options are also available (see spec list below).

Duo breakout view
(click image to enlarge)

Tubeware also touts the system for its amplifier, which provides 1.15V (+3.4dBu) input sensitivity, among other qualities. The Duo is further equipped with a 24-bit DAC and 100 Watt stereo speakers with 10Hz-20kHz range.


The Duo’s phono line-in jacks are said to be RIAA-equalized, and a pair of line-in jacks, a sub jack, and a video jack are also provided. Additional I/O extended from the Raspberry Pi includes a 10/100 Ethernet port, dual USB 2.0 host ports, and an HDMI port.

Duo rear panel
(click image to enlarge)

You can control the Duo via Android or iOS apps, or use the four-inch, machined analog control on the top of the device. The control is said to be cut from solid aluminum, balanced, and mounted to a high-resolution encoder. “With one knob you can adjust volume, switch inputs and set system preferences, while firmware updates allow you to create custom controls,” says Tubeware. The Duo is available in 10 front-grill color choices, and 27 custom choices, available for $19 extra.

The Duo is billed as a hackable, fully open source device, but for now, anyway, hardware details are somewhat limited. We were able to paste together a spec list from the partial specs, as well as the above photo of the back of the unit, and a few details gleaned from Engadget. Presumably full schematics will be posted once the device ships in May. In the comment Q&A, a company rep said Tubeware is working on a version of the open source XBMC media distribution designed for the box.

Duo color (left) and tube choices
(click images to enlarge)

Specifications for the Duo appear to include:

  • SBC subsystem:
    • Raspberry Pi Model B with Broadcom BCM2835 (1x ARM11 core @ 700MHz); VideoCore IV GPU; 512MB RAM
    • Optional Udoo Quad (add $110) with Freescale i.MX6Quad (4x Cortex-A9 cores @ 1GHz); Vivante GC2000 GPU; 1GB RAM
    • Fast Ethernet port
    • Wireless — WiFi, Bluetooth
    • 2x USB 2.0 host ports
  • Vacuum tube preamp (Electro-Harmonix ECC82/12AU7):
    • Design — Medium-Mu, twin triode
    • Dynamic range — >100dB (20Hz to 20kHz)
    • Frequency response — 10Hz to 20kHz (+0/-1dB)
    • Harmonic distortion — < 0.01% (SMPTE-IM)
    • Voltage gain — 93dB
    • Output circuitry — Class A
    • Max. input level — +14dBu
    • Max. output level — +28dBu
  • Other optional vacuum tube preamps:
    • Tung-Sol ECC82/12AU7 (add $25)
    • Electro-Harmonix ECC82/12AU7 Gold Pin (add $45)
    • Genalex ECC82/B749 Gold Lion Custom (add $75)
  • Main power amp:
    • Stereo mode — 8Ω / FTC 20Hz-20kHz / 0.1% THD – 100w
    • Input sensitivity — 1.15V (+3.4dBu)
    • Signal-to-noise ratio — (20Hz-20kHz) 8Ω > -100dB
    • Harmonic distortion — (SMPTE-IM) < 0.01%
    • Voltage gain — 31.6x (30dB)
    • Output circuitry — Class AB
  • Other A/V components — 100W Stereo speakers with 10Hz-20kHz range; 24-bit DAC
  • Multimedia I/O:
    • Right/left phono inputs (RIAA-equalized, with turntable support)
    • Right/left line inputs
    • Subwoofer audio out
    • HDMI out
    • Composite video out
  • Other features:
    • 4-inch machined control surface dial for analog control
    • 10x standard (27x custom/$19 optional) magnetic front grill speaker cover color choices
    • User-controllable RGB LEDs
    • RuneAudio and Volumio apps available
    • Android and iOS companion apps
  • Power — 48VDC, 3.125A input
  • Weight — 11.9 k (26.2 lbs)
  • Dimensions — 470 x 238 x 218mm (18.5 x 9.34 x 8.5 inches)
  • Operating system — Linux; Android also supported on optional Udoo Quad; XBMC support under development

Further information

The Duo is available now for a special pre-order $479 base price, which will rise to $649, presumably when it begins shipping in May. Orders that were placed the week of April 1 will ship between May 15 and June 1, while orders placed today on April 15 were said to ship in mid-July. More information may be found at Tubeware’s Duo website, and at its successfully funded Kickstarter project page.

(advertise here)

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