Metaxas Audio Systems Ikarus, Руководство пользователя

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K O S T A S M E T A X A S D E S I G N
D e s i g n P h i l o s o p h y
10
If we go back to our basic circuit and analysed the performance of an I.C.
positive voltage regulator (say a LM78LXX from NATIONAL SEMICONDUCTORS)
it would have an output impedance at the pin of its output lead of around
0.2 Ohms from DC to 10kHz, and then an increase to 0.4 Ohms at 20kHz, then
4.0 Ohms at 1 MEGAHERTZ which clearly illustrates the open loop frequency
response has a turnover point around 10 kHz. When you add the normal dis-
tance between the regulator output and amplifier circuits which may be as
little as 60mm to as much as 200mm in many circuits, the overall impedance
in creases 5 to 10 times. Also, to stabilise the operation of this I.C.
regulator, it is essential to use an output capacitor for stability.
Clearly, this is not good enough for high performance, high speed transistor
circuits. For this reason, we have approached the design of our regulators as
PART of our amplifier circuits, rather than make the fastest amplifier circuit
and add a slow I.C. voltage regulator with an output capacitor and call it a
finished design. Our discrete voltage regulators are designed to have the
absolute lowest noise, reject mains ripple, but more importantly to have a
speed (1000 V/microsecond) which is a result of their wide bandwidth design
(an open loop frequency response greater than 500kHz) and output imped-
ance which is an order of magnitude better than any I.C. The regulator
stability is achieved without ANY capacitors by varying the ratio between
the local and overall feedback of each device.
We position the regulators within inches of the active circuits (in the case
of the OPULENCE, the regulator is 3mm! from the active circuits) and the
regulator impedance is flat from DC to beyond 5 MegaHertz at less than
0.05 Ohms.
Beyond this electrical design aspect, we listen to the sound of our
regulators whilst developing each amplifier circuit to ensure that every
component change or substitution produces an audible improvement from
the selection of transistors to best biasing currents , choice of voltage
references zeners and degree of local feedback.
Marquis “wholistic” approach to Line Stage/Regulator