V A C U U M T U B E A M P L I F I E R S Y S T E M S
...the closest approach to the original sound
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The Quad
II-forty
THE QUAD II-FORTY valve amplifier is not only one of
the finest sounding valve power amplifiers available
today, it is an aesthetic and engineering masterpiece.
An understated elegance lies beneath the smooth curves
and lustrous finish, for the power amplifiers use a circuit
dating back over fifty years to the time when vacuum
tubes ruled the electronics industry and Peter Walker
was the master of audiophile design.
He often shunned traditional thinking, preferring to go
his own way, relying on excellence in circuit design.
Circuits that are still admired today by the finest minds
in electronics for their stunning performance and, by
today’s standards, simplicity.
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“Factor out nostalgia. Forget the miracle of Quad making
valve amps in the 21st century. Look at the Quads in terms
of a current pre/power tube combination. Then look at the
opposition. Now factor in gorgeous styling, superb build
quality, perfect ergonomics, ample grunt, genuine heritage
and the kind of sound which allows valve enthusiasts to
show two fingers to transistor users.”
– Ken Kessler, Hi-Fi News
The Quad II-forty power amplifiers are much more than
a tribute to one of the most famous designs in audio -
they are both refined and powerful in the modern sense
of the terms.
stunning, sitting safely within a cage to protect them.
Gold-plated phono connectors replace the ‘Jones’ plugs
of the original - with a choice of 4ohm or 8ohm taps,
allowing for the widest possible choice of loudspeakers.
Every product we make is hand-built by craftsmen for a
lifetime of duty. Quad products rarely, if ever, need
replacing and we regularly service and maintain
products over fifty years old.
Although the circuit topology has changed little from
the original, significantly better components and a
brand new transformer design - still delicately balanced -
means that they are fast, crisp and detailed, whilst
producing an output current, more than capable of
driving modern loudspeaker loads, even our own ESL
loudspeakers are well within their capabilities.
The champagne finished chassis is strong and heavy,
internally wired with solder tags - not PCBs. The KT-88
output valves in push-pull configuration are visually
This means many of the original Quad II amplifiers have
been passed down, into the hands of the children - and
even grandchildren - of the original owners, something
that is uniquely Quad in essence. A product that is
relevant today and will remain so for generations to
come.
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Quad products have always
been amongst the finest audio
products in the world. When Peter
Walker started making commercial PA
systems in 1936, few could have predicted
the revolution in hi-fi that many of his products
were to cause, the longevity they would have and
the esteem with which they would be held.
In the early 1950s, he and Gilbert Briggs, founder of
Wharfedale, embarked upon a series of now famous
concerts demonstrating how real high-fidelity music
should be virtually indistinguishable from a live
performance. In order to prove this they toured such
venues as the Royal Festival Hall in London and
Carnegie Hall in New York. Audiences were amazed at
the similarity the Quad amplifiers were able to
reproduce relative to the live performance.
Since these early demonstrations of true high-fidelity,
our product philosophy has remained constant, to
produce a sound which as closely as possible replicates
the experience of the live performance. For many other
manufacturers, the term hi-fi may mean ‘exciting’ or
‘dramatic’ and this can be easily produced without
regard to what the music sounded like in the concert
hall for the listener and may sound ‘impressive’ to the
uneducated ear, but in reality is no substitute for the
sound produced by ‘real’ hi-fi.
“Musicians and recording artists
all over the world have long
recognised the outstanding
quality of Quad products –
exquisite engineering, build-
quality, finesse and refinement.”
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The Quad
QC-twentyfour
Unlike the power amplifiers, the Quad Control unit
utilises a completely new circuit design. Once again, the
circuit is simple in concept yet remarkable in execution.
Our designers scoured the globe for the very finest
components, with possibly the best example of this
being the new ‘old stock’ 6111WA double triode.
Designed as a special military valve, it is hard wired to
the circuit and has an estimated life of nearly 100,000
hours. Together with transformers designed by one of
the World’s leading authorities and relay input
switching, the musical signal is preserved in its purest
form - pursuant to the philosophy of the theoretical
perfect amplifier which, as Peter Walker himself stated, is
‘a straight wire with gain’.
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“It is so much better in terms of high fidelity,
in its purest sense. It reminded me how Quad
retain an almost unique grip on the concept.”
– Noel Keywood, Hi-Fi World
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“Quad has succeeded where few of hi-fi’s gamblers
dare: They’ve followed the ESL-989 with not just a
worthy amplifier, but with a silent smooth and
precise control unit as well.” - Ken Kessler, Hi-Fi News
Peter Walker always believed that an amplifier should be
as simple as possible - engineer with the fewest possible
components and with a performance largely
independent of those components.
The total line gain is 15dB, with a high quality
potentiometer controlling the output levels.
Reminiscent of the original QC-22 control module,
there is a simple balance control allowing for variation
from left to right of up to 12dB.
The QC-twenty-four, a low-noise RIAA curve phono
stage has an understated elegant simplicity, although we
use high quality components wherever these appear in
the signal path.
Amplification is provided courtesy of a twin triode 6111,
new old-stock valve - originally designed for use in the
guidance systems of missiles and manufactured to
exceptionally high tolerances. The remarkably long
expected life-span of this valve means we can
comfortably build it into the PCB without the
compromises usually experienced when using valve
seats.
Bifurcated contact relays (crossing each other at right
angles to make a better contact) are used on each input
to maintain the best possible signal conduction. Gold-
plated connectors and a carefully screened enclosure
are further examples of the attention to detail
throughout the construction.
Two buffered tape loops are provided as standard.
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A completely new design, the QC-twenty-four pre
amplifier is both neutral and detailed. Using a military
specification 6111 valve, which is so reliable, it’s hard-
wired to the circuit board.
The standard QC-twenty-four is
line level only. There is an option
of a solid-state phono stage which
can be added when new, or at a
later stage.
Everything has been designed to maintain optimum
signal purity. From the relay switching to the gold-plated
terminals, each component has been selected for its
audio performance.
The chassis is painted to match both the Quad II-Classic
and the Quad II-forty power amplifiers, making it the
perfect partner to both systems.
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Designed by valve supremo, Tim DeParavicini,
the Quad twenty-four P is a stunning
addition to the range. Designed holistically
with the power and pre-amplifiers, it brings
an entirely new dimension to vinyl listening
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The Quad
QC-phono stages
For the analogue purist, the combination of a good
valve amplifier and a good turntable is the closest
possible approach to the original recording.
There are two options for adding such functionality to
our valve pre-amplifiers.
A solid-state module is available for the standard QC-
twenty-four pre-amplifier (known as the QC-24 phono
stage) which allows direct connection of a turntable
with an internal switch to change between moving coil
and moving magnet cartridges. This can be fitted as
standard or added later.
For the connoisseur however, there is the Quad twenty-
four P dedicated valve phono stage. This has been
designed for Quad by valve supremo Tim DeParavicini -
probably the finest valve amplifier designer in the world
today. It has been voiced by the finest ears in the
industry and will add an entirely new dimension to your
enjoyment of vinyl recordings.
This unit features a moving magnet/ moving coil toggle
switch on the rear, and a choice of direct full level
output, or a variable level output if you wish to connect
directly to a power amplifier.
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The Quad
II-classic
A faithful reproduction of the original, the new Quad II
Classic offers audiophiles the chance to recreate the
spirit and atmosphere produced from one of the most
famous amplifiers in audio history.
Peter’s circuit, notably the design of the output
transformer, has become the stuff of legend amongst
electronics engineers. Studied and analysed by the
finest minds in the industry, the elegance and
coherence of the design is still regarded as a reference
today.
The original Quad II was first launched in 1953,
designed by Peter Walker. At the time, many of his
contemporaries were also producing good quality valve
amplifiers. The Quad II looked, in comparison, very
simple and unassuming, but its performance was far
beyond that which its diminutive dimensions might
suggest.
Given the quite modest components of the day, he was
able to engineer something which was quite literally
greater than the sum of its parts.
The Quad II classic has been recreated accurately with
output valves and input valves the equivalent of those
used in the original design. The same balancing act has
been employed to ensure the same wealth of detail and
gentle tone of the original.
The property which set the Quad II amplifier apart from
other amplifiers of the time was its output stage. It was
arranged such that the cathode coupled circuit emulated
the performance of triode operation, but with the size
and efficiency characteristics of pentode operation. It
was this breakthrough that ensured the Quad II was to
remain in continuous production until 1970.
The output valves produce around 15w per channel,
operating in Class A which, although slight by modern
standards, allows a gloriously sweet and refined sound
with appropriately matched contemporary loudspeakers.
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‘the closest approach to the original
sound...’ has been a Quad philosophy since
1936. More than just a slogan, it underlies
the company’s commitment to producing
the finest audio equipment, capable of
reproducing all the elements and emotion
of a live performance.
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Quad sound systems have always provided high levels of
listening pleasure to their owners. Our philosophy has
always been one of reproducing the ‘live’ experience in
the comfort of your own home.
“The Quad II Classic uses
the finest quality
components, each hard
wired onto a robust
Whilst many modern amplifiers are stunningly accurate
and offer breathtaking resolution and distortion figures
in tiny fractions of a percent, many also loose sight of
the overall aim - which for Quad, is to bring pleasure to
the listener by recreating the entire range of sensory
experiences felt at a live performance.
chassis with solder tags..”
For many audiophiles, just as vinyl will never be truly
replaced by digital music, the vacuum tube
communicates on an emotional level that can never
really be surpassed by a transistor based design.
The Quad II classic is one of the finest of these vacuum
tube amplifiers. Although small in dimension and
modest in design, the purity with which it conveys, not
just the musical score, but the sense of space; the
passion of the vocal and the range of textures from the
instruments in any performance, is without peer.
As a piece of audio history, the Quad II circuit was
pivotal in creating what we know of as genuine ‘hi-fi’
today. As a design statement, the Quad II is not only as
relevant today is it was over fifty years ago, it is
remarkable in its absolute longevity. Yet the only
important factor is that the Quad II Classic can bring the
same pleasure to today’s discerning customer that has
been experienced by generations of Quad enthusiasts.
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specifications
Model
II-forty
II-classic*
40W RMS
15W RMS
Power Output
0.3% @ 40W
0.03% @ 1W
0.3% @ 12W
THD @ 700Hz
Better than -80dB
10Hz–30kHz(+0dB/-0.5dB)
20 @ 700Hz
Better than -90dB
10Hz–20kHz(+0.2dB)
11.75 @ 700Hz
90Va maximum
8 ohm
Residual hum & noise
Frequency Response
Damping Factor
Power Consumption
Loudspeaker Taps
Valves
180W maximum
4 ohm and 8 ohm
2 x 6SH7 Input
2 x EF86 input
2 x KT88 Output
1 x 5U44G Rectifier
2 x KT66 Output
1 x GZ34 Rectifier
1V RMS
1.4V RMS
Sensitivity
*The Quad II Classic power amplifiers are supplied in matched pairs.
Model
Valve Complement
THD @ 1V RMS
QC-twentyfour
QC-twentyfour P
1 x 6111 twin triode
Valve Complement
THD
4 x 6111
‹0.08% (A-weighted)
20Hz–20kHz (+0dB/-0.5dB)
Better than 60dB
‹0.2%
0.02% @ 1W
Frequency Response
Hum and Noise
Input Impedance
Moving magnet
Moving coil
47Ω
10Ω
5Hz–50kHz (+0dB/-0.5dB)
Better than -80dB
15dB
Frequency Response
Hum and Noise
Stage Gain
High sensitivity
Medium sensitivity
Low sensitivity
1.3mV (MM)/130uV (MC)
2.6mV (MM)/260uV (MC)
5.2mV (MM)/520uV (MC)
Line Stage Gain
50k ohms
Recommended Min. Load
Inputs
Nominal output level
(ref 5.2mV, MM, Low)
Inputs
1.0
5 x Line level
2 x Buffered tape loops
Selectable MC/MM cartridge
1 x fixed line level
1 x variable line level
15 VA maximum
Outputs
Power consumption
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Quad Electroacoustics Ltd, IAG House, Sovereign Court, Ermine Business Park, Huntingdon, PE29 6XU
Tel :- 0845 4580011, Fax :- 01480 431767
www.quad-hifi.co.uk
The information in this brochure is subject to change without notice.
All rights reserved © 2004 Quad
Qu.V 15.10.2004
Quad is a member of the International Audio Group
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