Massdrop offers the Objective2 (O2) Headphone Amplifier for $69.99 with free shipping. That's the lowest total price we could find for this open-source amplifier in any design by $37. Based on the designs of audio engineer and blogger NwAvGuy, it features 2.5x (low) and 6.5x (high) gain settings, 1-ohm impedance, and 3.5mm audio inputs and outputs. It's can be powered by an AC adapter (included) or two 9-volt batteries (not included). Deal ends August 3.

Note: The final design may vary from the image. Until this deal ends, customers can add feedback to the item's discussion section to influence the final design and features of the device.