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manual abstract
So this has been our design philosophy: a vacuum tube preamplifier stage to take advantage of the audio properties of that technology and a solid state power stage as “transparent” as possible. Other important innovations concern the Mono/Pre Out and added use functions. Verdi Cento Integrated Amplifier 2/7 A AAAAU UUUUD DDDDI IIIIO OOOOF FFFFU UUUUT TTTTU UUUUR RRRRA AAAAspa Unit description 333 555 111 222 333 666 1. Power Supply 2. Vacuum Tube Preamplifier Stage 3. Power Stages 4. Protections 5. Mono/Pre Output 6. Pre Phono Stage 7. Functionality 8. Technical Data Verdi Cento Integrated Amplifier 3/7 A AAAAU UUUUD DDDDI IIIIO OOOOF FFFFU UUUUT TTTTU UUUUR RRRRA AAAAspa 1. Power Supply The Power supply is the basis of every audio device. The Verdi Cento Integrated amplifier has a very generous toroidal transformer with a dedicated secondary stage for each section of the unit. After each secondary stage there are regulation circuits for every section, let’s see it in some detail: Input Selection/Volume control/PrePhono/RECOUT Powers Supply A dedicated secondary stage and 4 voltage regulator provide the supply for the input selection section, volume control section, Rec Out output stage and Pre phono section. The pre Phono power supply is obtained by further filtering of the regulator output voltage via a low time constant RC square. Vacuum Tube Preamp Power supply A lot of care has been taken over the Vacuum tube Preamp power supply, because a Vacuum Tube differential pair (that is the structure we have used in the preamp section) will never be well matched enough to completely reject the power supply variations. So we have designed a discrete component voltage regulator to obtain a very stable voltage from the dedicated high voltage secondary. The voltage regulator output is further filtered by two very low time constant RC squares, one for each channel. In such a way we have completely eliminated the 100Hz noise component and using separated RC square for the channels also decreases the crosstalk and increases the “sound stage” definition. Vacuum Tube Heater We decided to use a dedicated secondary for the Vacuum tube heater, in this way it is possible to use a linear voltage regulator for the purpose avoiding potentially noisy switching type regulators. The heather voltage has been selected to have the best audio performance from the vacuum tube used. Verdi Cento Integrated Amplifier 4/7 A AAAAU UUUUD DDDDI IIIIO OOOOF FFFFU UUUUT TTTTU UUUUR RRRRA AAAAspa Power Amps Power Supply We have dedicated a secondary stage for each power stage channel to decrease the crosstalk and increase the “sound stage” definition. The power amps power supplies take advantage of the high power toroidal transformer and discrete high current rectifier bridge have been used to allow high current peaks. There are four 10000uF capacitors after the bridge for each channel (so 40000uF for each channel!) and a lot of capacity has been distributed close to the Power amps to provide the charge for fast audio responses. The big capacitors and the discrete bridge we have used allow the power stages to perform very highly in bass reproduction. The particular solutions adopted in the power supplies allow the realisation of the high signal to noise ratio expected from the power stage circuit used. 2. 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. Verdi Cento Integrated Amplifier 5/7 A AAAAU UUUUD DDDDI IIIIO OOOOF FFFFU UUUUT TTTTU UUUUR RRRRA AAAAspa 3. 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...