Perfectly balanced volume control
On the volume control side, the D-27.28 adopts a different scheme from traditional technologies. Indeed, in the case of a "classic" volume control, the device implements this function at the analog input amplification stage, via signal reduction using a potentiometer. As a result, the sound reproduction is directly affected by the quality of the potentiometer used, which can result in loss of detail or distortion. Even when using a high quality potentiometer, there is a loss of detail. In addition, regardless of the quality of the potentiometer, this system also impacts the Signal to Noise ratio (SNR).
To overcome this weakness, Audio-GD chooses to use an I/V Converter (Transimpedance Amplifier). Thus, volume control results from a passive variable voltage current conversion at the ACSS output amplification, where 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 model allows to maintain the frequency band of the flat signal and therefore not to lose any detail. There is therefore no deterioration in sound quality, regardless of the volume level. Just after this volume control, the brand also integrates a group of 4 diamond buffers without feedback in the output stage, allowing to obtain a very low output impedance.
The quality of volume control is particularly important in a symmetrical system. Indeed, it must guarantee the accuracy of the signal control on the four channels to obtain a perfect balance. Otherwise, significant distortion would be created, which could even greatly limit the value of a symmetrical system. To maintain this balance, Audio-Gd also integrates a 4-channel digital relay control to modify the Vishay resistors and thus avoid imbalance. This allows the D-27 to have an extremely powerful volume control for high quality sound reproduction.
Finally, the DAC volume control can vary over 100 steps to achieve 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 for use with headphones or high or low sensitivity speakers.