Astreus represents a structural leap towards tubes with the intention of taking advantage of the physiological pleasantness of tube sound but also to bypass the negative structural limits imposed by output transformers on tube amplifiers and a number of other shortcomings of tubes related to adaptability to a wide range of different headphone impedances.
This carefully designed hybrid overcomes with ease.
The result is a very sophisticated presentation full of details with microdynamics that confuse you, bringing to the stage finesse that we did not notice on well-known tracks.
As the first step in the construction, the input buffer is made with an ECC 88 /6922 tube that gives the basic character of the sound. The input of the tube buffer is directly exposed to the source without volume control. It must be taken into account that the maximum input voltage to the tube buffer is approximately 5V (peak to peak). Definitely avoid DACs without output regulation and with a voltage greater than 6V (peak to peak). High output voltages of the source are unnecessary and undesirable in this case because the tube input is sensitive.
The next step in this hybrid topology is the 99-step volume control that allows for flawless regulation regardless of the sensitivity of the headphones, thus avoiding input and output attenuation with the aim of good volume control.
Advanced two-level volume memory functions facilitate comparisons with headphones with a significant difference in sensitivity.
The tube sound is transmitted via germanium transistors at the input stage of the power amplifier. The simple and effective application of germanium has preserved the general character of the tube sound.
The output stage operates in class A up to 5W of power. For higher output levels, it switches to class AB, avoiding unnecessary dissipation.
The powerful output stage is insensitive to headphone impedance and the number of headphones connected, so it can easily drive 4 headphones at the same time without any loss of playback quality.