Quad Electroacoustics

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This article is about the hi-fi manufacturer. For the music project, see Quad (music).
Quad Electroacoustics Limited
Private limited company
Industry Home entertainment equipment manufacturing & distribution
Founded 1936
Products Hi-fi equipment
Parent International Audio Group
Website www.quad-hifi.co.uk

Quad Electroacoustics is a British manufacturer of hi-fi equipment, based in Huntingdon, England.

Corporate history[edit]

The company was founded by Peter J. Walker in 1936 in London, and was initially called S.P. Fidelity Sound Systems. In 1936 the name was changed to the Acoustical Manufacturing Co. Ltd. The company moved from London to Huntingdon in 1941 after being bombed out of London in World War II.

The company initially produced only public address equipment but after the war they began to produce equipment designed for use in the home as a result of the rising demand for high quality domestic sound reproduction. Within a few years the company had transitioned almost entirely to manufacturing models for the home audio market.

Peter Walker Quote December 1975 technical paper in ‘Wireless World’ magazine

‘An audio power amplifier is required to produce an output signal that differs from the input signal in magnitude only. It must therefore have occurred to every circuit designer that it should be a simple matter to take a portion of the output, compare it with the input to derive an error signal. It is then only necessary to amplify the error signal and add it to the output in the correct amplitude and phase to cancel completely the distortion of the primary amplifier.’

Peter put this principle into practice using two amplifiers per channel instead of one. The first stage ‘error’ amplifier is low powered but very high quality. The second amplifier is high powered, but of lesser audio high quality. (It’s a lot more difficult to achieve very low distortion in high powered amplifier stages). Peter designed a way to compare the high powered output with the original audio input and derive the required error correction signal which is then injected into the audio path, in such a way that the high power audio output achieves a very low distortion figure, even at very high power levels. This innovative product earned Quad the Queen’s Award for Technological Achievement in 1978.

Peter Walker Quote 1978

"An amplifier should, within its limits of voltage and rate of change of voltage, (which is slew rate limiting) if you keep within those two it should be very much better than any program material. These are the things that are measured at .01 per cent or .05 per cent. But what is listened to is usually a program with 2 or 3 per cent distortion in the first place. That's the least you can get on records, tapes, and such things. Listening tests are usually not done in this region of .01 percent distortion. I'm quite convinced within that range the amplifier is just as perfect as you like to make it. It's quite possible to put 50 amplifiers in cascade, each one into a load, potted down into the next one, and to listen to the 50th one or to listen to the first one, and the sound will be virtually the same. So I think you can make an amplifier just as good as you like, and no more different than a piece of wire. But where they vary, when these tests are done, are a whole lot of areas. To start with, you can compare one amplifier with a bass cut-off of 20 Hz and another one that goes right down to DC. If you've got a program with a bit of fluffing going on at 5 Hz or so, the speaker cone in one case will be moving, and in the other case it won't be moving, so the sound from the speaker will be different. This isn't really a condemnation of the amplifier, it's that they shouldn't have this 5 Hz stuff there in the first place. So if you compare an amplifier with a straight wire, you've really got to make the straight wire have the same bandwidth as the amplifier, and the same terminating impedance as the amplifier. Once you do all these things, then the amps will be just as good as the straight wire. The peripheral effects are what get people into trouble. You can see why you find these differences in amplifiers. You can always find them. If people test two amplifiers and say, "These sound different," there's no magic in it. Spend two days, maybe a whole week in the lab, and you find out exactly why they're different and you can write the whole thing down in purely practical, physical terms. This is why these two sound different, and the cause is usually peripheral effects. It is not really a case of good or bad amplifiers, it's that the termination impedances are wrong, or something of that sort. We designed our valve (tube) amplifier, manufactured it, and put it on the market, and never actually listened to it. In fact, the same applies to the 303 and the 405. People say, "Well that's disgusting, you ought to have listened to it." However, we do a certain amount of listening tests, but they are for specific things. We listen to the differential distortion - does a certain thing matter? You've got to have a listening test to sort out whether it matters. You've got to do tests to sort out whether rumble is likely to overload pickup inputs, or whether very high frequency stuff coming out of the pickup due to record scratch is going to disturb the control unit. But we aren't sitting down listening to Beethoven's Fifth and saying, "That amplifier sounds better, let's change a resistor or two. Oh yes, that's now better still." We never sit down and listen to a music record through an amplifier in the design stage. We listen to funny noises, funny distortions, and see whether these things are going to matter, to get a subjective assessment. But we don't actually listen to program material at all". END QUOTE

Peter Walker was also attributed with the famous hifi quote "the perfect amplifier is a straight wire with gain" --- the implication being that nothing would be added, and nothing taken away from the signal, just a bigger version of the same thing at one end. It was an aim, a goal, a description of the perfect amplifier - nobody, including Mr. Walker, ever said they'd attained that goal, and even if they did, the chances were that they were severely handicapped by their test equipment at the time.

The name "QUAD" is an acronym for "Quality Unit Amplifier Domestic", used to describe the QUAD I amplifier. In 1983, when having become known for their QUAD range of products, the Acoustical Manufacturing Co. Ltd changed its name to QUAD Electroacoustics Ltd.

In 1995, QUAD Electroacoustics Ltd was bought by Verity Group plc, joining its existing brands of Wharfedale and Mission. A few changes were made, including shifting all production to Shenzhen, China.[1]

In September 1997 the company changed ownership again as Verity Group sold off businesses to finance its development of flat panel loudspeakers. With Wharfedale it became part of the International Audio Group under the management of Bernard and Michael Chang. Since Walker's death in 2003, the firm has had only its design ethos—"the closest approach to the original sound"—in common with the British hi-fi firm he founded in 1936.[2]

In 2003, a book was commissioned "QUAD The Closest Approach" which offered a history of the company from its creation to that point.

Audio products[edit]

The company's first products were released in 1948. The QA12 and QA12/P were low-powered mono valve designs. This unit's sound quality reproduction was high compared with other products on the market at the time, and was thus adopted for use by the BBC.


Quad 33 pre-amp
Quad II power amplifier

Following the mass production of 'stereo' vinyl records in 1958, the QC 22 control unit was developed and released in 1959. This was a stereo control unit that was designed to be used with a pair of QUAD II mono power amplifiers. To complement the QUAD II, the company also produced AM and FM tuners for use with the QC II & 22 control units.

The company made the transition to transistor-powered models in 1966 with the "professional" QUAD 50 monoblock which had a tapped transformer output and in 1967 the consumer Quad 33 preamplifier and 303 stereo power amplifier combination.

Control Unit – Pre Amplifiers

Quad 33 – 1967 to 1982 – 120,000 units
Quad 34 – 1982 to 1995 – 41,000 units
Quad 44 – 1979 to 1989 – 40,000 units
Quad 66 – 1986 to 1997 – 12,000 units
Quad 99 - 1999 to 2002

Stereo Power Amplifier

Quad 303 – 1967 to 1985 – 94,000

Current Dumping Power Amplifiers

Quad 405 – 1975 to 1982 – 64,000 units
Quad 405–2 1982 to 1993 – 100,000 units
Quad 306 – 1986 to 1995 – 25,000 units
Quad 606 – 1986 to 1997 – 27,700 units
Quad 707 - 1997 to 1999
Quad 909 - 1999 to 2002

Integrated Amplifier

Quad 77 - 1994 to 1999


Quad electrostatic speaker

In late 1949 (or early 1950), the company launched the CR corner ribbon loudspeaker. This used a Goodmans Axiom 150 cone loudspeaker for the lower frequencies and an electromagnetic ribbon loudspeaker, designed by Acoustical, for the higher frequencies. Fewer than one thousand units were sold.

In 1957, the released Quad Electrostatic Loudspeaker (ESL), the first production full frequency range electrostatic loudspeaker renowned for sonic transparency and very low distortion. Its sonic neutrality and transparency were offset by its extreme directionality, moderate power handling, the need for a large room, and moderate bass extension; its novel electrical characteristics could render some amplifiers unstable, which could result in damage to either or both.

The ESL was quickly adopted by the BBC for monitoring the sound quality of their broadcasts. The BBC eventually replaced them with moving coil based monitor speakers developed by several manufacturers, such as the highly successful LS3/5A, that were more easily transported and stored, and were more representative of typical contemporary hi-fi speakers.

Quad launched ESL-63, successor to the original ESL, in 1981. The newer design featured larger panels and an innovative stator design, made up of eight concentric rings fed from the centre outwards through analogue delay lines, so that the audio signal radiated out as though emanating from a single point. Subsequent electrostatic models, the 988/989 and then the 2805/2905 were successive refinements of the ESL-63 design, featuring increased power handling and output levels, more sophisticated overload protection, and greater structural rigidity.

Following the Verity acquisition, Quad developed and market a range of conventional electrodynamic loudspeakers alongside its electrostatic line, available in both passive and active (i.e. featuring in-box amplification) configurations.

All of Quad's products, including the ESL57, are still serviced by the Company's Service Department in Huntingdon.


Quad have always had a very straightforward engineering view of their products, and insisted that all amplifiers of adequate quality sounded the same when used within their capabilities, and that speaker cable had no sound at all, unless ludicrously long and thin wire is used.

To verify or disprove that amplifiers of adequate quality sound the same, Quad commissioned James Moir to organise and conduct listening tests comparing Quad II, Quad 303 and Quad 405 amplifiers. Statistical analysis of the expert listening panel's scores showed that "the decisions of the panel were no better than might be expected from sheer chance".[3]

The company's founder, Peter J. Walker, died in 2003 at the age of 87. He had retired in the late 1980s, then turning management over to his son Ross Walker.


A Quad L-ite satellite speaker provides the audio for a concert at home.
  • 1936, S.P. Fidelity Sound Systems founded by Peter J. Walker.
  • 1936, The company name changed to the Acoustical Manufacturing Co. Ltd.
  • 1941, The company moved to Huntingdon.
  • 1948, The QA12/ QA12/P amplifiers – the first product for domestic (consumer) market
  • 1950, QUAD I, (15 watt mono amplifier) released. Discontinued 1953.
  • 1953, launched the Quad II amplifier, made until 1970.
  • 1957, released the ESL, first production full-range electrostatic loudspeaker (aka ESL-57). Licensed to Braun in 1959 (loudspeaker BRAUN LE1)
  • 1959, the QC 22 stereo control unit released along with separate AM and FM tuners.
  • 1966, launched the first mono transistor amplifier, the 50 and 50/E, for the professional market.
  • 1967, launched Quad 303 stereo amplifier for domestic use, accompanied by the all-transistor QUAD 33 control unit.
  • 1975, The Quad 405 power amplifier released. replaced by the later MKII version known simply as 405–2 in 1982.
  • 1978, Queen’s Award for Technological Achievement in 1978.
  • 1979, launched Quad 44 preamp
  • 1981, new electrostatic loudspeaker, the ESL-63.
  • 1982, launched Quad 34 preamp
  • 1983, changed its name to QUAD Electroacoustics Ltd.
  • 1986, launched the Quad 66/606 system, along with the first QUAD CD player.
  • 1994, launched the Quad 77 Integrated stereo amo and components.Wins European Amplifier of the Year award for the 77 Amplifier.
  • 1993, launched the Quad L series dynamic loudspeakers.
  • 1995, Quad Electroacoustics Ltd acquired by Verity Group plc, joining its existing brands, Wharfedale Speakers and Mission
  • 1996, Manufacture of ESL-57 transferred to QUAD Musikwiedergabe.
  • 1997, Quad acquired by International Audio Group September 1997
  • 1999, released the QUAD 99 system; resurrected the legendary QUAD II and the QUAD II-Forty
  • 2000, released the ESL-988 and ESL-989, based on the legendary ESL-63
  • 2006, released the ESL-2805 and ESL-2905, redesigned versions of the ESL-988 and ESL-989.
  • 2006, released the L2 series loudspeakers.
  • 2008, released the Quad II-Eighty valve monoblock, designed by Tim de Paravicini.


  1. ^ CHINA: Behind the scenes at IAG | whathifi.com
  2. ^ Wharfedale Achromatic WA-S1 Speaker System | Home Theater
  3. ^ note evidently written by Quad staff and titled "QUAD COMPARATIVE AMPLIFIER TESTS, TUESDAY 21st MARCH, 1978" posted on Yahoo Newsgroup quadhifi, 6 November 2011.

External links[edit]