Quad

Peter Walker's electrostatics — the closest approach to the original sound

History

Quad Electroacoustics was founded in London, England in 1936 by Peter Walker as the Acoustical Manufacturing Company. The name "Quad" came from Quality Unit Amplified Domestic—reflecting Walker's goal of creating high-quality audio equipment for home use.

Peter Walker was a true visionary who believed that audio equipment should disappear, leaving only the music. His philosophy was expressed in Quad's slogan: "The closest approach to the original sound."

The Quad II amplifier (1953) established Walker's reputation for innovative tube design. Using a unique "cathode-coupled" output stage, the Quad II delivered 15 watts per channel with exceptionally low distortion. It remained in production for nearly 20 years.

The ESL-57 electrostatic loudspeaker (1957) revolutionized speaker design. Using a thin, charged diaphragm suspended between perforated stators, the ESL-57 eliminated the box coloration and moving mass of conventional speakers. It is widely considered one of the greatest speakers ever made.

The 1980s brought the ESL-63, an improved electrostatic design that addressed some limitations of the original. The 606 and 909 solid-state amplifiers continued Quad's tradition of British engineering excellence.

Today, Quad continues as part of the International Audio Group, still producing electrostatic speakers and amplifiers that honor Peter Walker's legacy.

Key Facts

Legendary Products

Quad ESL-57 (1957-1985)

One of the most important loudspeakers in history. The ESL-57's electrostatic design eliminated box coloration and moving mass, producing a transparency that remains the benchmark for many listeners. In production for 28 years.

Quad II (1953-1970)

A legendary tube amplifier that demonstrated Peter Walker's innovative circuit design. The Quad II's "cathode-coupled" output stage produced just 15 watts per channel but with exceptionally low distortion and beautiful sound.

Quad ESL-63 (1981-1999)

An improved electrostatic speaker that addressed the limited bass and power handling of the ESL-57. The ESL-63 used a segmented diaphragm and delay lines to create a more coherent wavefront.

Quad 303 (1967)

A solid-state power amplifier that brought Quad quality to transistor technology. The 303's "triple-emitter follower" output stage was innovative and reliable, making it popular for professional and home use.

Sound Signature

Quad's electrostatic speakers produce a transparency and purity that conventional box speakers simply cannot achieve. The ESL-57's charged diaphragm has virtually no mass compared to a conventional cone driver, which means it starts and stops with extraordinary precision. The result is a midrange clarity that makes vocals and acoustic instruments sound almost holographically real — there is no box coloration, no cone breakup, no resonance. Just the music, presented with an honesty that can be revelatory.

Peter Walker's amplifiers complement this philosophy perfectly. The Quad II's 15 watts per channel sound like more because of their exceptional quality — low distortion, beautiful harmonic structure, and a warmth that pairs ideally with the ESL-57's transparency. The 303 solid-state amplifier brings Quad's low-distortion philosophy to transistor technology with equal success. Across the range, Quad equipment embodies Walker's belief that the best audio equipment disappears, leaving nothing between you and the original performance.

Collecting Quad

The ESL-57 is one of the most important loudspeakers ever manufactured and remains the definitive Quad collectible. In production for 28 years, it established the electrostatic loudspeaker as a viable alternative to conventional speakers. Paired with a Quad II tube amplifier and a Quad 22 preamp, it forms what many consider the most musically satisfying vintage system ever assembled. The ESL-63 improved upon the original with better bass extension and power handling, using a segmented delay-line design that produces a more coherent wavefront.

The 303/33 solid-state amplifier and preamp combination is Quad's most practical vintage electronics, offering reliable performance with enough power for most domestic situations. When buying ESL speakers, the condition of the electrostatic panels is paramount — listen for any crackling or arcing, which indicates panel deterioration. Specialist ESL restoration services exist and can rebuild panels to original specification, but this adds significant cost. Quad amplifiers are more straightforward to maintain, with well-documented circuits and good parts availability.

Competitors & Comparisons

Quad vs ESL designs: Quad invented the category

Quad vs Magneplanar: Different approaches to panel speakers

Quad vs Box speakers: Quad eliminates box coloration

Amplifiers

• 33 — Vintage stereo preamplifier from Quad's iconic 33/303 series, known for modular design and high-fidelity performance. With detailed specs.
• 405 (1975) — High-fidelity stereo power amplifier with current dumping technology from Quad, introduced in 1975. With detailed specs and production dates.
• 405-2 (1979) — Quad 405-2 (1979): 100W per channel of current-dumping British muscle, DIN-only inputs, no controls, and a market that's quietly outgrown its old price guide.
• ii — Monoblock tube amplifier from Quad with KT66 tubes and Williamson-inspired design, renowned for high-fidelity sound and engineering excellence.

Cd Players

• 67-CD — Quad 67-CD: Quad's second CD player, a 1990s British deck with Philips CDM 9 transport, Delta-Sigma conversion, and 116 dB S/N per Audio's 1994 review.

Power Amplifiers

• 50 — Quad 50 (c.1975) power amplifier, documented only in a 1975 Studio Sound review. 50 watts into 100V line, low distortion, versatile bridging input.

Preamps

• 44 (1981) — High-end preamplifier from Quad with discrete Class A circuitry and modular design, renowned for transparency and build quality.

Receivers

• 4300 — No verifiable documentation exists for a Quad 4300 audio product. Archive sources reference Marantz, Chadacre, and Flojet 4300-inch models instead — none are Quad.
• fm-multiplex-decoder — Valve-based FM stereo decoder for BBC broadcasts, part of Quad's iconic tube-era lineup. Covers the complete spec table.

Speakers

• 15 — Quad 15 — little-documented model; likely a misattribution or colloquial reference to the Quad II amplifier's 15-watt output.
• 18 — Quad 18 — no period documentation found; the model's identity is unconfirmed. An honest record of a barely-documented Quad model.
• ESL (1957–?) — Quad ESL (ESL-57) full-range electrostatic loudspeaker, introduced 1957. 15Ω nominal, 50Hz–10kHz, external EHT supply, stacked-pair mods.
• esl-2805 (1981) — High-fidelity electrostatic loudspeaker with transparent sound and advanced panel design from Quad. This page has detailed specs and production dates.
• esl-63 (1981–1999) — Quad ESL-63 (1981–1999) electrostatic loudspeaker — Peter Walker's concentric-stator point source, 8 ohms nominal, 25 kg per panel, $1,500–$3,500 used.
• ESL-63PRO — Quad ESL-63PRO electrostatic studio monitor — the professional variant of the legendary ESL-63, demanding 15-100W into 8 ohms, with capacitor degradation and scarce parts to consider.

Tuners

• am (1971) — High-performance AM/FM tuner from Quad's professional series, renowned for exceptional reception and audiophile-grade sound quality.
• am3 (1971) — FM/AM tuner from Quad's acclaimed 33/303/AM3/FM3 series, known for exceptional reception quality and low distortion. Includes full specifications.
• amii (1973) — FM-only tuner from Quad's second-generation separates lineup, known for precision reception and low distortion. Find full specifications here.
• fm (1975) — High-end FM tuner from Quad featuring PLL stereo decoding and precision engineering for exceptional audio fidelity. Find detailed specs here.
• fm2 (1969) — High-performance FM tuner from 1969 featuring PLL stereo decoding and exceptional sensitivity and selectivity. With full specifications and production years.
• fm3 (1975) — Quad FM3 (1975) FM tuner — twin-lamp tuning, ceramic IF filters, PLL stereo decoder. Part of Quad's 3-series with the 33 preamp and 303 power amp.
• FM4 (1982–1988) — Quad FM4 FM tuner (1982–1988) — microprocessor presets, Schotz IF, PLL decoder, £249.60 at launch. One of the best-sounding tuners of the 1980s.
• fmii (1970) — High-fidelity FM tuner from Quad with excellent sensitivity and low distortion. Includes the complete spec table and when it was made.
• hr1 (1978) — Quad HR1 FM-only tuner from 1978 with PLL stereo decoding and high-precision reception for exceptional audio fidelity. Covers detailed specs.

Other Models

• 33/303 (1967) — Quad 33/303 (1967) — Quad's first all-transistor preamp/power amp pair, with the Triples Class B output circuit covered in the technical press.
• 50E (1966–1983) — Quad 50E (1966–1983) solid-state mono broadcast amp — 50W into 8Ω, output transformer, 600Ω line bridging, 100V line drive.
• 66 preamp — Quad 66 preamplifier — a two-box, fully remote-controlled preamp with no controls on the chassis, seven inputs, and RC-5 CD control.
• 66FM — Quad 66FM tuner — 19 presets, 88-108MHz, 76dB mono S/N, built as part of the Quad 66 remote system. Reviewed by Stereo Review in 1993.
• ESL-57 — Quad ESL-57 electrostatic loudspeaker — 93dB max output, 45Hz–18kHz, 18kg panels, 30–15 ohm load. The original boxless reference.
• FM1 (1959–1968) — Quad FM1 (1959–1968) valve FM tuner — no built-in power supply, Foster-Seeley discriminator, optional multiplex decoder. A brilliant mono tuner that needs the Quad Series 2 stack to run.
• QA12P — A low-powered mono valve power amplifier, the first product from Quad, Released and adopted by the BBC. Covers the complete spec table and when it was made.