VTL S-400 II series Owner's Manual page 6

The Design Goals and Benefits
When the VTL design team began developing the concepts for a next-generation Reference amplifier, the following
design goals were laid out:
•
The Reference amplifier should deliver a new sonic standard worthy of its marque as a member of the VTL
Reference family – it should provide unsurpassed sound quality into real-world loads, as well as excellent
measurements on the test bench
•
The amplifier must be able to drive a wide range of speaker types to their optimal performance, with
consistent performance under a wide range of conditions
•
The amplifier must be self-optimizing and provide a full range of diagnostics for maintaining peak
performance and providing user feedback, without the need for the user to have to know the inner workings
of the amplifier.
•
The operation of the amplifier must be intuitive and user-friendly while providing flexibility in its control
functions, for integration with modern home theater systems
•
Complete in-system diagnosis via front panel or remote to make remote use and maintenance easy.
These goals have been fully realized in the new S-400 power amplifiers.
S-400 Series II Circuit overview:
An all-tube amplifier, S-400 is the culmination of VTL's most advanced thinking in performance engineering, with self-
optimization, fault diagnosis and user feedback designed to bring the ultimate performance and convenience to the
user.
The Series II version of the S-400 features a complete re-working of the entire signal path. Upgrades include a fully
balanced differential input stage driving a differential phase splitter and a lower impedance push-pull output stage with a
dramatically improved, fully balanced and enhanced interleaved and coupled output transformer.
The S-400 Reference stereo amplifiers gain further sonic benefits with a shorter, faster and fully balanced negative
feedback loop, with zero global negative feedback. The negative feedback loop completely eliminates ringing and
requires no capacitor compensation to maintain critical phase integrity and information. The result is an amplifier that
remains stable even under the most demanding loads.
Adjustable precision-regulated plate, screen and bias supplies hold the output tube operating point constant even under
AC and main power supply fluctuations, and stabilizes the critical power supplies yielding tonal stability and sonic
integrity especially during complex, dynamic signal conditions.
Another new feature in Series II is a user adjustable Damping Factor feedback control that allows the user to adjust the
amplifier's output impedance by varying the amount of negative feedback. Impedance can now be precisely set to suit
the listener's taste, and to improve control of the loudspeaker loads to deliver best performance. The three possible
settings are:
1. LOW -- Lowest damping factor, good loudspeaker control, most natural sound.
2. MED -- Better loudspeaker control, with some impact on sound quality
3. HI -- Best loudspeaker control, with a little more impact on sound quality, but on speakers that need the
control the sonic improvement is clear
S-400 Amplifier Owner's Manual
VTL
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