We started with 250 OHm DT-990 Beyerdynamic Studio headphones connected directly to the Fractal DAC passive output (distortion of active linear circuits completely eliminated) this served as temporary reference. For driving headphones with lower impedance we need some kind of amplifier or buffer and here is where the problems started. We lost resolution and the transparent realistic music reproduction of our reference as soon as we added any conventional amplifier or buffer circuit. To rule out DAC related issues we performed tests with analogue audio sources and concluded this was not a specific DAC related issue. Apart from the well known amplifier issues we found a number of new fundamental amplifier issues that have been neglected for many decades. We managed to fix all these issues using a kind of servo feedback system that senses and corrects headphones membrane movement. This way the headphones membranes accurately track the headphones buffer input signal, reducing distortion to very low levels. It senses the back emf and ac voltage produced by the voice coil and uses this for servo feedback. Conventional headphones amplifiers are based on an open loop steering system, in this case there is no guarantee that the headphones membranes will accurately track the input signal, so distortion is likely to increase. The audible effects with conventional headphones amplifiers are mainly distortion and loss of resolution. So what exactly does this mean in terms of perceived sound quality with the SHPB10? Music is reproduced very realistically and with utmost transparency. Imagine that only the music remains and all unwanted side effects (distortion, loss of resolution, grain) have totally vanished. The SHPB10 is a buffer (gain = 1x) so less attenuation is required (improved SN ratio). It can drive all dynamic headphones and efficient speakers. It comes with a matching external stabilised mains power supply (2 x 5V safe low voltage). Both supply voltages are connected using two standard USB interlinks. This external power supply keeps magnetic field from the transformer and mains noise away from the headphones buffer. The SHPB can handle input signals up to 2Vrms. Both, L and R channels are present on each 3.5mm sockets (common ground connection).