One might not think the market for tube amps compatible with Raspberry Pi would be that big, but as it turns out, it seems to be. Recently, Pi 2 Design started a Kickstarter campaign for its Hybrid Tube Amp - the 503HTA. The campaign had a funding goal of $20 000, which has been surpassed (actually doubled) with 28 days still left on the clock. 

Now Raspberry Pi users can get the "sweet tube sound" as Pi 2 Design puts it for $99. The 503HTA is compatible with all Raspberry Pi single board computers and capable of handling headphones between a range of 32 to 300 ohm. The design for this model is based on the Bravo V2 amp, according to Pi 2 Design, with a class-A output stage added to the mix. Along with the high fidelity audio on offer, Pi 2 Design says the dedicated heater supply on this unit ensures no crosstalk whatsoever.