Velluto - Circuit Description
Low voltage supply and input stage:
The signal input can accommodate either unbalanced (RCA) or balanced (XLR) inputs, without the need for adaptors or shorting pins. This is accomplished by using an input coupling transformer. Transformer inputs also eliminate ground loops between the amp and the preamp. Ground loops not only cause annoying hums, but can lead to loss of low-level detail, as such musical information can be buried in the noise. Additionally, a coupling transformer will prevent any RF energy from entering the input, and causing further degradation of of the musical information from RF energy that would normally enter an amplifier input.
The input signal is further buffered through JFETs, in order to tailor the frequency response to yield a pleasing, yet accurate, frequency response. While it is possible to make an amplifier that has ruler flat frequency response, we decided to provide the listener with a frequency response that is comparable to other products to which they are accustomed to. The frequency response does allow for listeners to experience the finer details and nuances in musical reproduction that audiophiles have come to expect, without being fatiguing.
Each channel has its own toroidal transformer for the low voltage power supply. The power supply design features dual level regulators, the final one being the discrete wideband regulator that we use in all of our products.
Output supply and module:
The amplifier module is located beneath the low voltage/input PCB in its own metal enclosure. All Class D modules will produce EMI, and we have elected to place ours inside its own metal enclosure. Not only does this eliminate EMI from escaping, it has the additional advantage of reducing any shock hazard. To further reduce the possibility of EMI from escaping, all leads into and out of the amplifier module are treated with ferrite materials that absorb stray EMI.
A common toroidal transformer supplies the voltage for the output stages. Each channel has its own winding, independent of the other. While in theory, one channel could modulate the other, our tests have shown that this is not the case during normal operation. In fact, the supply current for each module is supplied by the filter caps, except during sustained periods of high output. Technically, one could make the case that this does not qualify as true dual mono operation. We had made measurements that indicate that use of two separate transformers will only add to the cost, and not to the performance. If it did, we would have chosen to use two smaller ones, instead of one oversized one.
The output terminals use Cardas "Patented Binding Posts" to connect to the speaker leads. We chose them for their ease of use and ability to keep the leads attached at all times.