Cello Duet 350 Owners manual
DUET 350
OWNER'S MANUAL
Serial Number
Table of Contents
Page
Product Concept and Description
Packaging and Features
The Rationale for High Power Amplification
Compatibility
Summary
Unpacking
Installation
Cable and Adaptor Selection
Custom Made Cables
Electrical Connections
Operation
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Bridged Operation Diagram
Cello Limited Warranty
Warranty of Repair Work Performed
Product Registration and Transferability
Tampering/Abuse/Misuse
Service
Maintenance
Specifications
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INTRODUCTION...
Congratulations on choosing the Duet 350 Amplifier. Your unit has been individually
handmade from the finest parts and materials. The Duet 350 utilizes proprietary Cello
circuitry that represents true state-of-the-art in audio electronics and is designed to
perform to "as-new" specifications for decades of musical enjoyment. We want your
Duet 350 to provide you with complete satisfaction. Please read this manual carefully
and care for your Duet 350 so that it will retain its value, beauty and performance. If
you have any questions, contact your authorized Cello Designer or call the factory. It
is our wish to assist you in every way, now and in the future.
Product Concept and Description
In 1986 Cello introduced the Performance Amplifier, a no-compromise four chassis
set of two mono supplies and two mono amplifiers. The Performance Amplifier has
become a legend in its time because of its extremely natural sound, lightning-fast
response, almost unlimited power, and exceptional reliability. While the Performance
Amplifier was designed as a reference standard without cost restrictions, the more
affordable Duet 350 offers a similar combination of qualities in a single, stereo
chassis.
the Performance, with 40 output devices per channel, has greater output current for
driving ultra-low impedance loads. For most 4 to 8 Ohms speakers, the Duet 350 is
the natural mate. Its twelve output devices per channel, coupled with the most
sophisticated circuitry, give it tremendous capabilities. In normal stereo mode, it has
more than enough power to drive most speakers to their limits with the kind of open,
clear, effortless sound coupled with high speed and powerful dynamics that are the
hallmark of Cello. In bridged mode, accomplished with the flick of a toggle on the
rear panel, the Duet 350 becomes a devastating 1.2 kiloWatt mono block power
station for those who have the speakers to withstand it. In stereo or bridged mode the
Duet 350 is the music lover's dream-come-true amplifier.
The principal difference between the Performance and the Duet 350 is that
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Packaging and Features
The Duet 350 chassis is an imposing 11 inches (28cm) high. The height is designed
to accommodate a number of vertically large subassemblies including circuit boards,
heatsinks, and power supply components. In particular, twelve large output devices
per channel require substantial heatsinking. As an alternative to fan cooling, large,
vertically-oriented passive heatsinks are provided for each channel.
2
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.
they cannot be electrically conductive. This requires the transistor to be electrically
insulated from the metal, but thermally connected via mica wafers.
Most other power amps have the heatsinks on the outside where
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. Heavyduty 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.
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