Perfectly balanced volume control
As far as volume control is concerned, the D-27 adopts a different scheme than traditional technologies. Indeed, in the case of a "classic" volume control, the device implements this function at the level of the input analog amplifier stage, via the reduction of the signal thanks to a potentiometer. As a result, the sound reproduction is directly impacted by the quality of the potentiometer used, which can result in a loss of detail or distortion. Even when using a high quality potentiometer, a loss of details can be noticed. Moreover, whatever the quality of the potentiometer, this system also impacts the Signal to Noise Ratio (SNR).
To overcome this weakness, Audio-GD has chosen to use an I/V Converter (Transimpedance Amplifier). Thus, the volume control results from a passive current to variable voltage conversion at the ACSS output amplifier, for which the output is the current signal and not the voltage signal. Therefore, the volume depends on the conversion of the current (I) to a voltage (V).
This design keeps the frequency range of the signal flat and therefore no details are lost. Therefore, there is no degradation of the sound quality, whatever the volume level. The brand also integrates just after this volume control a group of 4 diamond buffers without feedback in output stage, allowing to obtain a very low output impedance.
The quality of the volume control is particularly important in a balanced system. Indeed, it must guarantee the accuracy of the signal control on all four channels to obtain a perfect balance. Otherwise, distortion would be created, which could limit the interest of a balanced system. To maintain this balance, Audio-Gd also integrates a digital relay control on 4 channels allowing to modify the Vishay resistors and thus avoid unbalancing. This allows the D-27 to have an extremely efficient volume control for a high quality sound reproduction.
Finally, the volume control of the DAC can be varied over 100 steps allowing a wide control range of 90dB. Moreover, this control is exponential. Thus the volume progression is very smooth over the first 50 steps allowing a simple and precise adjustment, whether it is for use with headphones or high or low sensitivity speakers.