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Special Design
Features
Rugged Build
Quality
M echanical strength has been a hallmark of Perreaux products since the
company first started production back in 1974. The concept behind the physical
design and construction is that each structural member should contribute to both
rigidity and performance.
Ultra Stiff
Power Supply
The 750 incorporates a massive custom designed, toroidal power transformer,
employing unusually heavy gauge wire that reduces copper losses to a
minimum. An electrostatic shield prevents AC line borne interference from
entering the signal path. The power supply filter capacitors, totaling 60,000µF,
have exceptionally low inductance and internal resistance. They charge and
discharge in response to load demand far more rapidly than conventional storage
capacitors and are capable of delivering the instantaneous current required by the
output stages, providing optimum dynamic range and transient response. The
wiring from the power supplies to the output boards is designed for unimpeded
transmission of the required current and voltage and utilizes heavy gauge, tinned
copper wire cables. Since power supply leads radiate at signal frequencies, all
wiring is carefully loomed to minimise this effect.
Hybrid Class
A/AB
The bi-polar transistors used in the 750 are run in Class A mode. This avoids the
crossover notch distortion and the resulting odd-order harmonics present, to
some degree, in all other classes of operation. The devices used in the 750
output stage are M OSFETs, which with high quiescent current circuitry, are run
in the equivalent of Class A to 10 watts. Beyond this point the output class is
technically Class AB (hence the hybrid nomenclature), but with a major
difference. The combination of M OSFET characteristics and their application in
this circuitry, result in crossover distortion so minimal that it is virtually non-
existent.
MOSFET
Output Stage
The 750 output stage takes full advantage of the unique qualities of M OSFET
devices and in many ways they are superior to bi-polar transistors. A major
advantage is their tendency to draw less current over a large section of the power
bandwidth as their temperature rises (Negative Temperature Coefficient), hence
self stabilising thermally, whereas bi-polar transistors draw more current as their
temperature rises (Positive Temperature Coefficient) and protection circuits
become mandatory to prevent thermal runaway and eventual self destruction.
MOSFETs have the ability to swing fully across the amplifier’s internal DC
voltage and are therefore true "rail-to-rail" devices. Using M OSFETs
encourages the highest performance from the balance of the internal amplifier
circuitry.
Multiple
Protection
Systems
The 750 is equipped with a number of protection systems, isolated from all
signal carrying circuits via opto-couplers, to protect both itself and ancillary
equipment.
