The 503HTA, Hybrid Tube AMP/DAC is a small Hat size raspberry pi add-on developed by Pi 2 Design.

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It connects to the PI I2S port and its Burr-Brown PCM5102A DAC drives a single 12AU7 tube gain stage with solid state Class-A output.

It is designed to drive stereo headphones from 32 to 300 ohm quite easily.

The design was derived from the popular Bravo V2 architecture with all the modifications recommended such as:

IRL510 Output MOSFET

Regulated Heater Voltage to eliminate cross-talk

Adjustable Plate Bias for easy Tube Rolling

Nichicon MUSE Audio Output Capacitors

Jumper-able output impedance of 1.5, 32 and 100 ohm plus switchable gain selection to match your headphones exactly

The 503HTA also has an on-board 5V at 3A regulator, thus allowing the HAT and the Pi to be powered from a single, 24V external supply.

Pi 2 Design writes:

“Prototype testing is complete and the performance matches or beats that of much higher cost tube amps. We are planning a Kickstarter campaign to begin in the next week or so.”

The first 503HTAs with a JJ Electronics 12AU7 tube will sell for $99 including the 24V at 2A supply.

See also: Getting Hi-Fi sound from Raspberry Pi

See also: Arduino drives Smart Nixie Tubes with LED highlighting