BEYOND
THE ABSOLUTE
In the Marche region, a geographical area world-famous for the production of esteemed musical instruments, Audison started its long history in the pursuit of audio preformance perfection.
BEYOND
THE GENESIS OF
HV VENTI
As early as 1991, HR 100 stood out as a benchmark, bringing the Audison brand into the Olympus of Hi-End manufacturers.
HR 100 was designed to obtain the highest sound quality without compromises. Its maximum power output was its only limitation, as technology of the time did not allow this reference sound quality with massive power. Four years later the THESIS brand was reated. Using the latest technology, Audison once again rewrote history on amplifier performance. In 1995 and in 1996 respectively, HV sedici and HV trenta amplifiers came to light.
THESIS and HR 100 have a strongly distinctive sound, which could not be improved in its uniqueness, but one way to try was: to merge the two projects into a single amplifier, long-held in the dreams of
Audison designers. After two years of research, with HV venti, the dream became true.
HV VENTI
"THE AMPLIFIER"
Like its predecessors, HV venti is an absolute reference product for the years to come, indelibly marking the history of Hi-End mobile electronics.
“The Thesis HV venti sets new standards in the world of car audio amplifiers. Only an extremely experienced designer could have created such an exclusive product. The six-stage power supply, the twomode
amplifier (high current, high power), the completely hi-end, discrete devices and straight sound path will be well appreciated by the musical enthusiast. But it’ s only the result of a deep reconsidering of the meaning of the mobile amplifier concept. Every part of the Thesis HV venti was a rethink, and every single
component was optimised using the most exclusive devices, solutions and materials. Every electronic, mechanical, thermal and aesthetical aspect was improved by going back to the beginning. The Thesis HV venti is the wonderful synthesis of an extraordinary engineering effort.”
Absolute lack of compromise in achieving maximum performance, this is the mantra followed by the Audison R&D for the HV venti, a project with the following unique features.
Output power stage based on an innovative topology similar to IGBT (Insulated Gate Bipolar Transistor) but employing discrete devices.
Total void of integrated operational circuitry that, due to their
constructive technology and the low voltage level can deteriorate the signal. Their elimination allowed the engineers to work at higher voltages and with a Class biasing of the intermediate stages.
All signal commutations were treated using special relays: too
complex of a circuit would have led to longer tracks and parasitic inductances, causing signal deterioration and loss of musical information.
The whole input circuit is balanced up to the final stage “Front End”, while the amplifier’s configuration is “Dual Mono”.
In order to avoid electro-magnetic interferences, no high current is passed on the main board.
HV VENTI UNIQUE DESIGN
OUTPUT POWER STAGE
The output power stage is based on an innovative topology similar to IGBT (Insulated Gate Bipolar Transistor) but employing discrete devices.
The circuit is made from a complementary pair of Hitachi DMOS drivers, usually used as output stage devices (such as in HR100), which drive two pairs of SANKEN power BJT transistors providing each with 30 A peak current capability and 200 W dissipation.
This solution allowed the use of only two pairs of output devices,
thus permitting bias currents which necessarily have to be shared according to the number of output devices in parallel to be reduced; therefore, increasing the bias current value on every output device is possible, keeping the total current absorbed by the amplifier stable when in idling status. All this leads to the increase of the output stage to A class value.
The percentage of A Class and consequently the idling current
can be adjusted via the BIAS current diverter. As a result of the
configuration of the HV venti in Hi Power or Hi Current mode, there will be a variation of the A Class percentage and therefore of the idling current also.
CROSSOVER
To guarantee maximum sound quality, the crossover was made on a separate module supplied with the product.
Available adjustments are Hi Pass/Lo Pass 12 dB and Lo Pass
24 dB mono. Four cut-off frequencies are selectable for the filter
(45; 55; 65; 80 Hz). Although this solution is limiting compared
to a continuously adjustable cut-off, filter linearity is drastically
improved and long signal paths are avoided.
PREAMPLIFIER AND DRIVER
It is made of two groups, Front End pre-amplifier and control unit.
The whole stage is balanced up to the driver outputs. The power
supply voltage is 90 V and is specific for this stage and dedicated
to the two separate channels.
The separate 150 V power supply is thermally stabilized and A Class biasing. Input is balanced with the first stage, complementary JFET differential and the second stage, complementary BJT differential. The voltage amplifier is Cascode type with a buffer to drive the output stage.
POWER SUPPLIES
The product features two Hi power supplies for each channel
providing power exclusively to the Dual-Mono output stage.
Each channel power supply pair 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 allows engineers to increase the impulsive current transient response necessary to the amplifier.
Furthermore, the two pairs of power supplies were synchronized to reduce radio frequency electro-magnetic interference.
The layout featuring four separate power supplies has allowed
the use of a single powerful MOSFET for each power supply rail,
thus avoiding the paralleled configuration that is perhaps the main cause of amplifiers failures.
Each transformer and related filter inductor were enclosed in nonmagnetic metallic shells and then filled with resin.
This procedure further increases reliability for two reasons: first
of all, coils are blocked and therefore made immune to vibrations;
secondly, heat is homogeneously distributed, thus preventing any
possible overheated areas.
The resin-filled groups were then mounted onto the aluminium
thick bottom plate to allow heat to be dissipated through side
heatsinks.
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 to gather all output stage
return currents; the layout was created so that each current path
comes close with the return current flowing backwards. This way
the electro-magnetic fields are out of phase and nullify each other: this solution could be defined as a “balanced power supply”.
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