Published On: January 4, 2009
Last Updated on: October 31, 2020
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Quad 33 Preamp and 303 Amp Reviewed

Not a whole lot to say about Quad that hasn't already been said-they're good at what they do and have a hugely loyal fan base reticent of Apple. Whether you harbor feelings for their speakers or their electronics one thing remains the same, once you hear a Quad system it's hard to listen to anything else.

Quad 33 Preamp and 303 Amp Reviewed

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Aaah, if only every manufacturer had this dilemma - too many classics in its c.v.! With Quad, do you think first of the original ESL or ESL63? The Quad 22/II? Or do you picture their biggest-selling pre-amp ever and their second-best-selling power amp, the 33/303 combination? For those of a certain age, who arrived on the hi-fi scene after 1967 but before the dawn of CD, that was the heart of a Quad system, and for many of them, it was the introduction to the UK's most venerable brand.

Additional Resources

Check out our review of the mAMP at
Read audiophile preamp and amp reviews from the likes of Audio Research, Krell, Mark Levinson and many others at
Read about classic tube companies on's Tube Blog.

Quad-303-Amp-Reviewed.gifBy the mid-1960s, the transistor had made such broad inroads into audio that even valve die-hards like Quad, McIntosh, Leak and Radford were having to produce both. Difficult though it may seem for younger readers to envision this, there was a time when major brands' catalogues included both technologies.

Gordon Hill recalled, in , 'Quad was one of the last audio manufacturers to introduce a transistor amplifier...Many famous names were early adopters and they were a commercial, if not an audiophile success. The original Leak Stereo 30 is one such example.

Competition and Comparison
You can compare the Quad 33 preamp and 303 amp against other products by reading our reviews for the Unison Research Mystery One preamp and the Beard BB 30-60 integrated amp. You can find more information available in our Preamplifier review section and on our Quad brand page.

'In many ways Quad had built a rod for its own back. Prevailing transistor amplifiers had neither the power response nor the stability to drive the ESL-57 satisfactorily and the world at large would just have to wait if the remarkable qualities of this speaker were not to be thrown away by an unsuitable design.'

Unlike some, Quad did wait for a dependable device. It arrived in the form of the silicon epitaxial transistor, which Hill states, 'had virtually none of the disadvantages of its germanium cousin. There was a learning curve, but manufacturers did eventually produce high-gain, low-noise input devices and stable, wide bandwidth output transistors. The EF86 and KT66 were the devices of yesterday, the BC109 and the 2N3055 were the devices of tomorrow. Nearly 40 years on you can still find them, or some of their variants, in many modern amplifiers.'

Quad launched the 33 pre-amplifier and 303 stereo power amplifier in 1967 after a typically long gestation period. Many have noted that the Quad 33 is in many ways a solid-state Quad 22. Quad employee Roger Hill notes that, 'If you look at the Quad 22 and the Quad 33, it fits in the same furniture by just squaring off the corners.' The styling was brought up to date, allowing the unit to be free-standing or cabinet-mounted.

Quad provided mains power for the 33 to allow it to be used as a stand-alone unit and it had two switched sockets on the rear panel to supply mains to a tuner and a power amplifier. To maximise the available space, all the signal connections were DIN, at a time before the average audiophile grew to loathe them.

Its phono input is a conventional, two transistor amplifier with feedback equalisation, with a plug-in board to provide different cartridge sensitivities and impedances. (Moving coil was not a major concern in 1967.) Gordon Hill: 'The relatively low headroom of this stage requires that high output devices be attenuated, thus failing to maximise the noise performance of the preamplifier. This being 1967, all options for adjusting recording characteristics have been consigned to history and the response is within 0.5dB of the RIAA curve from 30Hz-20kHz. A built-in rumble filter cuts in steeply at 30Hz.'

A second plug-in board in the tape loop allowed the user to vary the output and input sensitivities, while the tape output could be adjusted to conform to the DIN standard. Gordon Hill remarked that, 'Those who were around at the time will recollect what a blessing that was. On just about every other British preamp of the period the presence of DIN sockets did not indicate conformity with the DIN standard!'

At the front, the 33 looked like no other pre-amp - other than a modernised 22. Customer loyalty was a huge part of the Quad client profile; to prevent culture shock for users moving to the 33 from the 22, Quad provided an extensive filtering and tone control system, with small rotaries for the tone controls, plus a row of press buttons for source select and filter settings. A primary rotary knob served the combined on/off and volume functions.

Its sister, the 303, was rated at 45W/ch into 8ohms, producing 28W into 16ohms and was believed to be unconditionally stable into any load. Gordon Hill felt that it was, 'Outstanding in partnership with the 16ohm ESL-57; the amplifier's performance features low distortion and a controlled bandwidth of 20Hz-35kHz, -1dB. As transistor amplifiers go, the output impedance is a relatively high 0.3 ohms, fine for 16ohm loads, less good into lower impedances. At very low impedances, performance falls off.'

Various iterations exit of the 303, including models adapted for pro use, but the basic model featured a special DIN-type connector to take the signal feed from the 33, with mains in via a 3-pin connector. Earlier versions (S/N 80,500 and below) used a miniature 3-pin Bulgin socket, while later versions use a 3-pin IEC connector.

Gordon Hill remains impressed with the 303. 'In complete contrast to today's design philosophy, the 303 uses a fully regulated power supply. The genius of the circuit lies in the innovative use of "output triples", which renders the current in the output stage virtually immune from temperature changes and ensures stable performance under widely varying conditions.' Additionally, Quad fitted the 303 with automatic current-limiting to render it virtually indestructible under nearly any combination of input and output, including an open circuit or dead short across the output terminals.

As for the sound, well, let's just say that a mint 33/303 combination will upset audiophiles who refuse to believe than vintage solid-state gear can produce satisfactory sounds. I lived with my 33/303 on a daily basis, using it 40 hours per week for four years, driving the LS3/5As on my desk. I found it so easy on the ears that, most of the time, I was simply unaware of its presence - high praise, I assure you. (While the ESL 57 is an obvious match, you simply hear it with LS3/5As.) Clean, sweet, devoid of the nastiness of most early tranny amps - it stood out amongst its contemporaries as a harbinger of doom for the commercial dominance of the valve.

Gordon Hill felt that, 'Certainly with 16 ohm loads, the amplifier behaves impeccably. On loads where the impedance plunges heavily at low frequencies, the amplifier can run out of steam and its 4 ohm performance is just about adequate. That said, there are thousands in current use all over the world and, in its day, the 303 was extensively employed in domestic, broadcasting and professional applications, satisfied users including (improbably) Pink Floyd.'

Inevitably, what goes around, comes around, and, as of 2005, Quad - as do McIntosh, Audio Research and others - produces both tube and solid-state ranges. This year, Quad relaunched a facsimile of the Quad II valve amp. But will they ever reissue the 33/303? Unlikely, and for two reasons. I was once told - emphatically - that both pieces would be too expensive to produce today, using the methods and technology of their day. Change the innards to surface-mount technology, ICs, etc, well, it wouldn't be a 33/303, then, would it?

And the other reason? The survival rates of both the 33 and the 303 are so high that, at any given time, the classifieds and the audio fairs are full of them, at bargain prices. And, yes, Quad will still repair them.

The 33/303 combination ranks amongst Quad's all-time best-sellers. As for the disproportionate number of 33 vs 303 sales, Quad accounts for that by reminding us that the arrival of the 405 power amplifier preceded the arrival of a matching pre-amp - the 44 - by four years, so a number of 405s were sold with 33s.

Quad 33 Control Unit: 120,000 produced, 1967-1982
Quad 303 Power Amplifier: 94,000 produced, 1967-1985

'My' Peter and Peter Bax [Baxandall] worked together on the 33 and 303 and did their triples [a way of making output devices so that the biasing wouldn't shift with changes of temperature], which then came out in 1967. That worked very well, so the 33/303 really started to motor, although we managed to build into the 33 a catastrophic failure.

They used to have these bloody little plug-in circuit boards that were frightfully dinky and frightfully clever and we thought we could change those for servicing, etc. It was done for all the right reasons. But the original edge connectors had tinned contacts and the boards were silver-copper, and of course with subtle vibrations they went through the tinning and oxidised, so you got resistance building up in them.

Read more about the crazy Quad story on Page 2 . . .


We started to get reports of intermittent performance and again we had a lot of internal arguments. I said, Look, something is wrong; we're getting far too high a failure rate. No, it's not, it's fine, it's fine. Because, of course, when we looked at it, it worked, because the first time you take a board out and put it back in, you get a connection. We had about a year of arguing before I could persuade people that there was a real problem out there. We then had to gold-plate the contacts. Unfortunately, because we had cracking after-sales service, everybody always thought the 33 was a very reliable product, when the first 20,000 all went bloody wrong.

Peter used to do the industrial design, including the 33/303, did it all and the office was just littered with mock-ups of what it might look like. The 303 was easy because the Quad II was this shape and we had a cabinet that it fitted in. 303 was exactly the same shape [as the II]. That was the way power amplifiers should be - actually, no good logic why a transistor amplifier ought to be like that other than that we had to get the power transformer in somewhere and what do you do with the electrolytics?

That was another interesting thing. The original electrolytics were installed this way up. As they warm up, they expand and when they cool down they contract, so they suck air in. The air bubble eventually rises to the top of the electrolytic so eventually they all void themselves onto the printed circuit board. Blaaap!! If you put them this way up, though, they just puff in and out at the top. We did that after about 50,000 of them. (Laughs.)

In many respects, actually in many ways [Peter] made life more difficult for our customers, although he thought he was doing them a favour. When the 33 came out, people said, 'I'm not buying it with that bloody marigold thing on it.' Well, Peter loved that, he thought this was great. And customers would come up and say, 'Well, I'm not going to buy that unless you take that marigold thing off. You'll have to change that.' And he'd say, 'Well, I'm not. Bugger off. Go and buy a Leak. Go on, bugger off.'

And actually, we did manage to sell quite a lot of those, but we'd have sold an awful lot more. There is absolutely no doubt in my mind that if we'd been a bit more - we were customer-friendly, but not 'customer-centric'...if you bought it, you got jolly good attention, but what about the other 99.99 percent of the population that didn't buy the bloody thing? Because they didn't like the fact that it was marigold, and actually it looked a bit peculiar and rinky-dink and of course that's why Yamaha and Pioneer and Sony came in and took over the world. Yes, they were good at manufacturing and we were absolutely crap at it.

No question, it went off like a rocket - I should imagine our business just about doubled the year that we brought [them] out. And it greatly expanded the overseas markets, too.

We got lots of flak from the press when we carried on making valve amplifiers when everybody else was making transistor amplifiers. And Mr. Walker said, 'We're not going to make transistor amplifiers until it's as good as our valve ones. As good as it sounds, its reliability, its price.'

A lot of the inside detail of the 33 was mine, but not the 303, and I did the test gear for the pre-amp. John Collinson - a clever chap, quite important to my training - designed the main circuit and it was finished by Mr. Walker. We started with Quad 22 test gear and a switch box. We did it all very carefully, we fed the same signal through and tested the prototype, and through the set under test, and used a differential amplifier to look at the difference. So as long as you looked at all the different circuits within the pre-amp, the semi-trained technical operator had to see a straight line all the while, whatever they did.

I might also have done some honing of the circuit, like the pre-amplifier for disc. I did the actual values selection; I didn't change the actual topology of the circuit. It's a detail thing. We didn't do anything for 78s at all, but we made the RIAA as close as we possibly could - nowhere near as good as the 44, but a lot better than the 22.

We were looking for a new preamplifier while the 33 was still running. So the 33 went on for a few years while we were making the 44. The things we wanted to do were all in the 44 - marketing wanted all of the inputs on separate modules so that it could be made to measure. They wanted more inputs than the 33. Mr. Walker and the senior engineers had been doing tests on tone controls, because no doubt you've heard Mr. Walker say that we put them on as a marketing exercise because our dealers said they couldn't sell the stuff without it. But we also put on the cancel facility, so that customers, having paid for these expensive tone controls could then switch them off. (Laughs.) The old-fashioned tone controls hadn't really much use once you'd got into the 1970s. They had when you were playing 78s, but not into the 1970s.

Check out our gallery of Ten Killer Amps below . . .
  • Tony Beef
    2022-06-09 23:50:34

    I have a 303/33 and a 405/33.I had them all recapped around 20yrs ago .Still sound Great !!

  • Anonymous
    2021-11-12 06:55:58

    Technically its class AB

  • David R Firbank
    2020-10-20 04:36:32

    A friend of mine gave me his 33 ser# 12122 and 303 ser# 4771, no operation instructions. It did have 2 circuit boards in the back of the 33. They are tenaciously logged in there and don’t want to come out. He also gave me a bag full of an assortment of plug styles. I never did use the set and without manuals have no idea how to connect them up to whatever. Is any operational data still available for these units? I think that in 2020 their simplicity is quite stylish, the Star Trek / Star Wars futuristic stuff is getting boringly common. Dave R Firbank Sr.

  • Dan
    2019-12-26 19:25:02

    Is this a class a amp?

  • Joe Bigliogo
    2016-04-15 00:27:07

    I very much like the 303 amp, less so the 33 preamp. As I remember in the late 70s it was the Quad 405 that got ballyhooed while the 303 was largely ignored as obsolete and transcended. Were we to honestly compare them we would realize that the opposite was true. The 405 (at least early production runs) sounds shrill and harsh by comparison. The 33 preamp I'm afraid I can't recommend stock. It's not that it's badly designed, the engineering is text book. Yet it sounds grainy, lacklustre with a quantity of sonic fuzz overlaid on the sound. How is this possible? It's the parts they unfortunately chose… 1968 and crappy. But that only means the solution is easy… a complete parts makeover and not difficult do to serviceable design. The preamp goes from dreary to astonishingly good. Not quite the transparency of the best but close enough and most of all… always musical. The 303 benefits from parts a upgrade too but the difference is not as dramatic as the 33. And I don't quite know why unless it's because the 303's stock parts were better. Whatever the case modern parts will transform this gear and probably lsat another 40 years. Not exactly cheap to get it all done but well worth it and certainly a lot less costly than springing for new components at today's prices.

  • Graham G
    2013-07-31 00:23:57

    I am still using a 33/303/FM3 with Morduant Short MS400 speakers all purchased from 1971 onwards and a recent high end CD player with attenuator,, and Monster cables. The Quad equipment was refurbished while I waited in the mid 1980s by Acoustical Engineering in Huntingdon for no charge in 1985. Since then, perfect. why change? I have a very powerful 5.1 system as well for TV and Blu-ray

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