What is stereo?

There are now two system of high fidelity, monophonic (monaural) and stereophonic. Monophonic is a system that starts from one microphone and is fed through a single high fidelity set. Stereophonic is a double system. Two separate microphones are placed at different sides of the orchestra and two different systems are used to keep the two signals or channels separated. Two separate speakers are used, placed on different sides of you room. Stereo is much like 3-D photography, two slightly different sound reach your ears giving you a new dimension in sound.

H.H. Scott '59

Quad II Integrated Amplifier

The Quad II-Classic Integrated
The rekindled interest in 2 channel analogue hi-fi been remarkable to witness. The popularity of vinyl has grown steadily over the last years and now represents a significant proportion amongst real music enthusiasts. Quad has been at the forefront of this trend with its development of some of the world's most stunning amplifiers  loudspeakers and phono stages. Creating a compact audiophile integrated solution for LP and Vintage Hi-End Audio lovers while working in collaboration with one of the industry's edteemed legendry figures, Tim DeParavicini.

Through his contemporary designs based on Qad's novel amplifier technology developed over half a century ago for his invention of the first Quad II Mono Amplifier introduced in 1953, our classic range of amplifier and speaker componenets represent far more than a nostalgic trip down memory lane. Each product represents as significant a design statement as their original counterparts.

The new Quad II Classic Integrated  Amplifier is perfectly balanced and completely integrated amplifier system to resolve system matching and offer exceptional performance nd value within a relatively compact and classically styled chassis.

Performance as you would expect from one of the most famous names in hi-fi, is nothing short of breattaking. The 25 watt per channel specified, belies their power and ability to drive even the most difficult loads. The remarkable output transformer design is characterized through its speed, agility and ability to convey the genuine passion of live performnce.

Design and Engineering
The KT-66 output valves, in push-pull configuration are visually stunning, even when safely secured within the cage tht protects them. Each valve produces around 25 watts per channel output in "Pure ClassA" which allows a suebrbly refined sound that appropriately matches modern as well as contemporary loudspeakers.

The package had to retainn the retro look of it famous preamplifier predecessor with th epower amplifier and transformers blended into a modern compact look. It has an understated elegance which lies beneath its smooth curves and lustrous finish because it uses a circuit dating back over fifty years to the time when vacumm tubes ruled the electronics industry and peter Walker was considered by many to be the master of audiophile design.

All Quad products are expected to last a lifetime - even longer. Many Quad customers still derive immense pleasure listening to products built over fifty years ago. The new Quad II Classic Integrated Amplifier is no exception, and with periodic servicing and a caring hand, you can expect its performance to continue for decades to come.

The Quad II Classic Integrated Amplifier operates in Pure Pentode (Beam Tetrode) output with partial cathode loading, this being more linear than so called ultralinear. It is a pure Class A operation, whereas its push pull operation's efficiency can only rach 50% max and its power supply is the usual capacitor filter with diode bridge rectifier, AC 6,3 volts heaters to the valves that is shared between both channels.

Equipped with a bi polar transistor phono amplifier that uses 4 transistors per channel with low feedback to provide correct RIAA equalisation. Also has a gain switch for moving coil caartridges, 0,25 mV at 1 kHz , a circuit which operates from a regulated 36 V derived directly from th emain HT valve. It ensures a very high overload performance from rcords.

The phono circuit is housed in a shielded compartment providing low noise RF proofing within th emain package.

Amplification Process
The Quad II Classic Integrated Amplifier output is 25 watt per channel  Integrated Amplifier had to obey Peter Walker's Philosophy  of cathode loading of the output stage and simplicity of design.
Upon Input, a selector switch routes the required signal to the volume control then on the first of 3 small driver valves. This first valve is an ECC83 acting as a differential balance circuit that is a phase slitter.
The output going into a pair of ECC88 valves that both operate as a cascode circuit for high gain and wide bandwidth directly drives the output valves (KT 66) via capacitors.
The circuit had to have high gain than a normal power amplifier to offer a nominal 250 mV input sensitivity on the various inputs.
Push pull feedback is arranged from the cathodes of the output back to the ECC88 valves to provide low distortion and noise with consistent performance.

Stereo Power Output:  25 W per channel into 8 Ω
Total Harmonic Distortion:  0,06% (at 15W &700 kHz )
Signal-to-Noise ratio:  better than -95 dB (ref 25 W into 8 Ω)
Frequency Response:  20 Hz - 20 kHz +0 dB -0,5 dB
Crosstalk: better than 75 dB
Gain :  34 dB
Noise:  -98 dB (275 mV input)
Valve Type:  4 x KT66; 4 x ECC88; 2 x ECC83
Input Channel:  3 x Line Level; 1 x MM/MC Phono and Tape monitor
Dimensions (W x H x D):  200 x 310 x 380 mm

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