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value on every output device is possible, keeping stable the total current absorbed by the amplifi er when in idling status.
All this results in the increase of the output stage to class A value.
This value is the typical car audio amplifi ers’ weak point. Due to installation needs, they always require several output
devices in parallel in order to work on very low loads and in the meantime to have low consumption since the car battery
supplies them.
This confi guration proved to be especially valid both in terms of power performance and of acoustic quality: the DMOS
power transistors used as driver supplies the current that the BJT output needs because their “current gain” decreases
when current increases. Thanks to the DMOS voltage amplifi ers’ specifi c feature, the confi guration used insures that this
gain decrease doesn’t overload in current the previous voltage amplifi er stage and it can have a constant distorsion for
every output load.
Also regarding the output power stage, an innovative solution was adopted.
In any amplifi er high supply currents, power output and return ground current create electro-magnetic fi elds interfering
with our precious audio signal.
In order to avoid this kind of situation, you are often forced to use convoluted wiring which compel designers to accept
compromises. Compromise is not accepted in the HV venti.
Inside the HV venti a six layer thick copper board was used which gathers all the output stage return currents; the layout
was created so that each current path comes to close contact with the return current fl owing backwards.
This way the electro-magnetic fi elds are out of phase and nullify each other: this solution could be defi ned as a “balanced
power supply”.
e) Power supplies
There are two Hi power supplies for each channel. They supply power exclusively to the output stage.
Each power supply pair of each channel works in Synchro- PMW mode: an independent circuit controls each of them.
However, they are synchronized with one another and are designed to supply one single power source, one supplies the
positive and the other the negative power.
This solution, which has been employed by Audison for a very long time, allows engineers to increase the impulsive
current transient response necessary to the amplifi er.
In HV venti this confi guration was doubled in each of the two channels: the amplifi er is actually set into a Dual Mono
confi guration, reducing interference between the channels.
Furthermore, the two pairs of power supplies were synchronized to reduce radio frequency electro-magnetic
interference.
The use of 4 separate power supplies has a further advantage.
Power split allowed the use of just one MOSFET, although a large power one, for each rail of each power supply, thus
avoiding the paralleled confi guration that is perhaps the main cause of amplifi ers failures.
Each transformer and relative fi lter inductor were enclosed in non-magnetic metallic shells and then fi lled with resin.
This procedure further increases reliability for two reasons: rst of all, coils are blocked and therefore made immune to
vibrations; secondly, heat is homogeneously distributed, thus preventing any possible overheated areas.
The resin-fi lled groups were then mounted onto the aluminium thick bottom plate to allow heat to be dissipated through
side heatsinks.
In the Dual Power function, each transformer was equipped with two secondary windings that are selectable by positioning
minifuses into the two available jumpers. For Hi Current confi guration you need 15A fuses, while for Hi Power confi guration
you need 10A fuses; the fuses are factory provided.
All the necessary adjustments for Dual Power confi guration are automatically managed by the ASC (Amplifi er Status
Controller) .
All the rest of the power needed for signal circuits are supplied by two Flayback power supplies, one for each channel.
They have reduced power but are high effi ciency types and are synchronized with the main power supplies. The whole
power supply group is connected to the car battery through two supply terminals equipped with a strip fuse. Two further
terminals are provided to connect an external capacitor.
f) ASC: Amplifi er Status Controller
The ASC unit (Amplifi er Status Controller) is in charge of managing all of the amplifi er’s confi guration functions.
It is equipped with its own proprietary microprocessor. Using the Status Display, you can visualize operational functions
or any possible anomalies of the amplifi er or of the external systems. The ASC also handles the protection circuits and
checks thermal conditions of each component and maximizes the fans to keep things under control. Vumeters are used
to identify output power.
- 6 -
DESCRIPTION
INTRODUCTION
2
7


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