Packaging And Features - Cello Duet 350 Owner's Manual

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Packaging and Features (Cont.)
To achieve a more affordable price, Cello engineers developed new circuitry which
offers outstanding performance without dual choke power supplies. The Duet 350
will drive speakers of any impedance, but it is optimized for loads in the 4 to 8 Ohms
range. Some speakers have a low impedance in part of their range. For example,
electrostatic speakers may have a dip in the range between 10 to 20 kHz. The Duet
350 handles such anomalies with complete grace.
The Duet 350, like the Performance Amplifier, has electrically conductive heatsinks
mounted inside the chassis. This approach has several advantages. First, it offers
maximum thermal transfer from the power transistor case to the heatsink. This
permits the maximum transistor power-handling capability to be obtained.
Second, there are no mica insulating wafers to short out and thereby causing
amplifier failure. Most other power amps have the heatsinks on the outside where
they cannot be electrically conductive. This requires the transistor to be electrically
insulated from the metal, but thermally connected via mica wafers.
Third, the heatsink becomes an electrical asset conducting voltage to the transistors.
Fourth, money that would have been spent polishing and anodizing heatsinks to make
them cosmetically perfect (heatsinks are manufactured as rough, industrial parts) can
be spent where it offers some real value - on premium circuits and parts.
The inner chassis of the Duet 350 is heavy steel for structural strength. The sides, top
and front panel are clear-anodized aluminum for long-lasting beauty. Custom-made
Litz wire, first introduced to audio by Cello, Ltd., is used throughout the amplifier for
signal paths, DC voltages and ground paths. Three-pin Swiss-made Fischer
connectors are used for balanced line input connections of the highest quality. Heavy-
duty speaker output connections are made via industrial-strength barrier strips with
#8 screws. Because of its substantial weight (95 lbs/ 43Kg), front and rear handles are
provided for safe lifting and moving of the unit. Protection circuitry is provided for
the amplifier's use in unsafe conditions without compromising sonic quality. The
power transformer is specially shock-mounted to minimize mechanical noise. Like
other Cello products, only premium parts (seldom, if ever, used by other
manufacturers) are used exclusively to ensure as-new Cello performance during
many decades of listening pleasure.