User manual AUDIO ANALOGUE VERDI CENTO 11-2008 INTRODUCTION

[. . . ] Other important innovations concern the Mono/Pre Out and added use functions. Verdi Cento Integrated Amplifier 2/7 AUDIO FUTURA spa Unit description 5 2 1 3 6 3 1. Technical Data Verdi Cento Integrated Amplifier 3/7 AUDIO FUTURA spa 1. The Verdi Cento Integrated amplifier has a very generous toroidal transformer with a dedicated secondary stage for each section of the unit. [. . . ] Vacuum Tube Preamplifier Stage The vacuum tube preamp section is the first active stage the audio signal meets in the unit and it is placed after the input selection circuit and the volume control. The Preamp not only has to amplify the signal and adapt the impedances but must also provide two out of phase signals to drive the bridge configured power stage. The unit is based on a "classic" and well-known scheme that we have developed to decrease the output impedance and match the application. Moreover, the fact that it produces zero feedback is its main outstanding characteristic. This means we haven't modified the vacuum tube distortion characteristics in any way and we have let the vacuum tube play "as it is" (remember the "philosophy". . . ). Nevertheless, the overall distortion is kept low with a higher power stage gain that lets the preamp section work with a low level signal at all times. Power Stage Our purpose was to have a solid state power stage as "transparent" as possible, able to provide/supply 100W in an 8Ohm load. So we have chosen the National Semiconductors LM3886 Power pack as a building block and we have designed a "parallel/bridged" power amplifier. We have decided to use such a component (we are not the first in this, see Jeff Rowland's Concentra Integrated Amplifier as an example) for its overall electrical characteristics (high power capability, high signal/noise ratio. . . ), its reliability and very good overall audio performance. The "parallel/bridged" structure we have used requires 4 LM3886 for each channel and allows sharing of the current demanded by the load among the 4 components. In such a way we can obtain more than 100W on an 8Ohm load and more than 170W on a 4Ohm load. The signal to noise ratio obtained is very good: for a load of 8Ohm with a 100W output power we have 99dB with no filter and 106dB Aweighted (with a noise gate of 0-500KHz for both the measurements)! 4. Protections Every sensitive part inside the unit has been protected to increase the reliability expecially in respect to the temperature increasing due to the high power capability of the product. As an example the LM3886 used in the power stage is a very reliable component (that's one of the reasons why we have choosen it!) protected against shortcircuits and overcurrent and it has two different temperature protection systems: one against instantaneous overtemperature and one against average overtemperature. We have introduced a termal protection into the toroidal transformer too to disconnect the primary if the temperature rises too much. And we have even introduced a thermost close to the power stage heathsink to detect the internal overall temperature and disconnect the loudspeakers if the temperature becomes too high, protecting in such way all the components in the unit. 5. [. . . ] Besides the traditional integrated functions it can be set in bypass mode to work as a Power Amplifier. Moreover, you can change the "volume scale" of the integrated amplifier to match it with your loudspeaker's efficiency and have the best volume resolution. Four different scales are available including a 1dB step scale and a scale adjusted for high efficiency loudspeakers! [. . . ]