This simple amplifier is ideal for adding a headphone jack to equipment that lacks this feature. The Headphone Buffer circuit board is small enough (1.2" X 1.4") to squeeze into even the smallest spaces and power requirements are so low that existing supplies in retrofitted gear can be used. It's a useful addition to many PAiA products such as the Submixer or Submix-Master. Adding a headphone output turns a Stack-In-a-Box it into an incredible practice amp.
The key component is the 5532 Dual OpAmp. While ordinarily this part is chosen for it's low noise characteristics, it is also capable of delivering nearly 350mW of output power per side, more than enough to drive headphones. The circuit can operate from bipolar voltages from +/-5V to +/-18V and it is not absolutely necessary that the + and - supply voltages be the same magnitude. The superior supply voltage rejection of the IC allows operation with unregulated supplies.
In the typical mono application such as adding headphones to a FatMan or Theremax, the Left and Right inputs of the amp are both connected to the Volume control supplied with the kit. For stereo applications a dual ganged pot should be used and this modification is covered in the instructions.
The Headphone Buffer amp kit includes circuit board, all electronic components, 1/4" Stereo Jack, Volume control w/knob, wire and assembly instructions.