Bringing the 'Sweet Tube Sound' to the Raspberry Pi
10 May 2016
Launching on Kickstarter, Pi 2 Design introduces the first Tube Amp specifically designed for any of the 40-pin versions of the Raspberry Pi SBC Family.
The 503HTA Hybrid Tube Amp HAT, designed and manufactured by Pi2Media (a division of PI 2 Design), is a high quality I/O shield designed to bring “Sweet Tube Sound” to the Raspberry PI family of Single Board Computers. This HAT allows the Raspberry Pi SBC to drive headphones from 32 - 300ohm with ease and fidelity.
Based on the popular Bravo V2 design with all recommended Mods, the on-board PCM5102A DAC drives the single stage 12AU7 (or 6922) tube. The Class-A output stage is comprised of the IRL510 and LM317A. The dedicated heater supply insures zero crosstalk.
In the company’s second PCB spin, it set out to improve upon the initial design specifications:
• Changed output mosfets (IRL510 & LM317) to TO-220 vertical through hole package. This will greatly improve the thermal solution.
• Added output relay protection to remove power on "thumps".
• Switched to bigger Anode Bias adjustable pots with mechanical stop.
• Raspberry Pi HAT compliant size w/40-Pin mating connector.
• 24-bit DAC - The well regarded -112db THD PCM5102 is used to convert the I2S Stream to drive the Single Triode Tube Stage at 24-Bit up to 192Khz Frame Rate
• Tube Rolling – The 503HTA supports both 12AU7( ECC82) or 6922/6DJ8 (ECC88) type tubes. Individual Anode Bias Adjustments plus selectable series/parallel heater drive insure the perfect setup for virtually any tube.
• Headphone out – Rugged 3.5mm Jack plus selectable output resistance between 1.5, 32 and 100ohms.
• Gain select switch – 3 Gain settings allow the user to select the output voltage to the optimal level for each headphone. Settings (based on 12AU7) provide approximately 2V, 4V and 6Vrms.
Every 503HTA will ship with a pair of adapter cables. The first is a 1ft. 3.5mm male to 1/4" female. This allows you to plug your high end headphones into the 503HTA.
The second cable is a 1ft. 3.5mm Jack to a pair of RCA Female Left/Right Stereo. This is to allow you to drive an amplifier with the 503HAT, on the lowest gain setting.
This project is on Kickstarter, click here for more information.