Audio Analogue VERDI CENTO User Manual

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Verdi Cento

Integrated Amplifier

Issue Date: November 2008

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Research & Development

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Introduction

Audio Analogue continues in Vacuum Tube/Solid State technology fusion research
introducing the Verdi Cento Integrated Amplifier to complete the audio chain begun
with RossiniCD Player REV2.0. We believe vacuum tube technology is, even now, very
valid in treating the audio signal in a preamplifier stage while leaving to solid state
technology the task of the Power stage. 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.

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Unit description

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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

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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.

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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.

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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 sharing of the
current demanded by the load
among the 4 components. It also
allows the use of a lower power
supply voltage. 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. Mono/Pre Out

Verdi cento has a Mono/Pre Output. This means the output
can be set to be a Mono Out or a Preamplifier output. If you
set it as Mono Out you can use it to drive a passive
subwoofer. If you set it as preamp out you can use the Verdi
Cento preamp Stage to drive a Power Amplifier to realize a
“bi amplified” system or just to use the Verdi cento as
Preamplifier. The Mono/Pre Out is easily set changing the
position of Jumpers on the board with the only simple but
essential recommendation of to not do it with the unit on.

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6. Pre phono stage

Verdi cento has a pre Phono section able to treat both MC and
MM signals. You can easily set the Pre Phono Mode changing
the position of Jumpers on the board. We have chosen this
kind of Mode selection because it permits you to perform the
Pre Phono settings without increasing the track’s length and it
avoids the low level signal from the cartridge passing through
selectors.

7. Functionality

Verdi Cento has a new set of functions that makes it very flexible. 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! Furthermore, the Verdi
Cento has the balance function as well.

All the components used are high quality and low tolerance. The Board that is often a
neglected “component” has been designed respecting all possible noise reduction techniques
especially for the current return parts and power supply traces.

8. Technical Data

Dimensions (Nota 1)

Weight

Line Gain 4,6dB
Power Amp Gain 32,5dB
Phono Gain 60 dB (MM), 80 dB (MC)
Line Input impedance 40KOhm
Phono Input impedance 56KOhm (MM), 100Ohm (MC)

Power on 8Ohm load:

Power on 4Ohm load:

Frequency responce (Note 2) 150KHz

Responce to a Square Signal (Note 4)

Signal Noise Ratio (Note 3)

Noise level (Nota 5) -100dB
Inputs 1 Phono Input + 5 Unbalanced Input
Outputs 1 tape Out + 1 Pre/Mono Output

Notes:
Nota 1 - Height x Width x Depth
Nota 2 - Attenuation 0dB, -3dB band
Nota 3 - Attenuation: 0dB A weighted reffered to 8 Ohm load nominal power
Nota 4 - 8 Ohm load nominal power
Nota 5 - Band limits 0Hz-40kHz

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103 x 448 x 405 mm

4,0 x 17,6 x 15,9 “

12,5 Kg

27,5 Lbs

1W @ 0.03% THD + N
10W @ 0.05% THD + N

100W @ 0.15% THD + N

110W @ 0.16% THD + N

10W@0.04% THD + N

170W@0.3% THD + N

Vout: 80Vpp

Rise time: 2.8uS

106.20 dB (A weighted)

99.30dB (No filter)