Headphone amplifiers from Ear Stream are unique devices in the fields of circuit choices and assembly techniques. Both have ground in several years of experimentation and endless hours of listening sessions and fine-tuning of the solutions on any imaginable level of construction. Outer simplicity of the circuits is a result of selecting very sophisticated integrated circuits, mostly dedicated for broadband applications performing heavy tasks in cable networking. Their parameters fullfil much stronger requirements regarding frequency response, slew rate and settling time than those dedicated for audio, providing really high fidelity of reproducing the music with its full bandwidth, dynamics and transient accuracy.
The aforementioned goals are achieved by using short and fast negative feedback loops which provides the negative feedback deliver advantages only - very low harmonic distortion, output impedance, TIM and intermodulation products. It should be mentioned that most disadvantages and negative impact on the sound caused by negative feedback appears in circuits with long feedback loops, with frequency response often shaped to fix instabilities resulting from other unfixed issues, which is even worse. There are no such solutions in Ear Stream amplifiers.
In order to guarantee full availability of the parameters provided by the active parts of the circuit, our headphone amplifiers are equipped with fast and efficient power supplies. These are either batteries or dual stage linear regulators build in specific goals in mind:
At first, no time constant or negative feedback loops. You will find no bandwidth limiting capacitors or filtering inductors in our power supply circuits. These is particularily important for audio to prevent power supply from oscillations and response delays when the load has a dynamic impedance. So, the first stage of the regulation is a low impedance discrete voltage follower with the reference built on a Zener diode supplied form a minimalistic current source. Such circuit provides instant response to any change in the current sunk by the amplifier circuit. The second stage in the Sonic Pearl 2 amplifier is the best available LDO regulator preserving operational stability without capacitors at the input and output. This means that there is no need to bypass its output with ceramic or tantalum capacitors. So, the output voltage is only trimmed to the desired level with further filtering applied by a single solid state device adjusted with a single, high precision resistor.
Another advantage of Ear Stream headphone amps is DC coupling from input to output combined with single supply voltage. When you look at electron tube circuits, there is in most cases a single rail dedicated to supply certain cicuit sections. In Sonic Pearl 2, Black Pearl and Headonic this is also the case. The "floating" ground has many advantages easy to explore especially in preamplifiers and headphone amps. The first of them is DC output impedance independent from AC impedance which is important for the music signal transmission. In Ear Stream headphone amps the DC impedance is high enough to keep your headphone safe in case a DC offset voltage appears because the output current shall be limited to a level below 30mA if not further limited by the headphone impedance. On the other hand, there are no input or output capacitors degrading the sound quality.
The assembly technique of Ear Stream headphone amplifiers should be considered as point-to-point despite the fact that you can see a printed circuit board supporting the components. Actually it has no other function as all the leads meet in the same soldering point and the only traces utilized are power supply rails and the ground. Both are reinforced with a bare wire and soldered on the whole surface. The results are: shortest possible signal path between components due to spatial arrangement and low impedance of connections due to no traces involved in conduction.
Component selection has been done on two levels - first come parameters and then thorough selection between matching parts delivering desired sound quality. Such tuning might take several years when starting from scratch and the final result is two fold. On one hand, we obtained the optimal bill of materials and on the other hand we know which parts are bad and will never be used in current and future designs. We don't look at the prices. You can realize that the Sonic Pearl 2 or Headonic is a mix of cheap and expensive components whose selection wasn't target price driven. If you see other components in competition's interiors, mostly electrolytic capacitors broadly advertised as good and don't find in our amps, these for sure weren't good enough for us.