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Quad 405/405-2 Power Amplifier Review

In this second article in my Quad 405 series, I review the legendary Quad 405-2. Find out why so many love these amazing little amplifiers and why you should buy one – a real one.

The Quad 405 was and remains an incredible amplifier, even now, some 40+ years after it was introduced to the world. This article you are reading right now is one of the most popular articles on my site. That should tell you something about the Quad 405’s enduring qualities and how people are drawn to these lovely amplifiers.

For more, check out my updated Quad 405-2 restoration and Quad 405 refresh articles!

Tellingly, the Quad 405 and 405-2 are most loved by those for whom listening to music is more important than looking at power meters, fiddling with controls and discussing technical specifications. It’s curious, but this little industrially styled amplifier punches well above its weight, all these years later.

Don’t get me wrong, I love power meters, but the 405 is a study in elegant, stripped back, understated design. It’s a true champion of the ‘less is more’ philosophy and an amplifier that just gets out of the way and plays music. Surely this is what every true hi-fi lover wants in an amplifier?

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Is it just me or does the 405 look like it came straight out of the 1940s?

Quad 405 vs 405-2

The Quad 405 and 405-2 are almost identical, compact, heavy, power amplifiers. Both punch out 100 watts per channel, into 8 ohms. Where they differ is in their ability to deliver current into lower impedances.

Specifically, Quad modified the current limiting circuitry of 405-2 to be a little less aggressive. There’s a wider power envelope with the 405-2, allowing it to better drive lower impedance loads. If you own current-hungry speakers or those with a nominal 4 Ohm impedance, a 405-2 is the better option.

Quad also implemented various iterative improvements over a long period. In my opinion, the later amplifiers sound and perform slightly better. If you are interested in more technical detail, I recently overhauled a Quad 405-2 and you should also check out the ‘Further Reading’ section at the end of this article.

Innovation

Quad’s legendary design engineer Peter Walker utilised a principle called ‘feedforward error correction’ in the 405 design. He wrote a paper about it, which you can read here.

Quad405 2
This is a schematic, representing a typical iteration of the 405 layout. Note that this is one entire channel, minus the power supply transformer. Not a lot there really…

As Stereophile pointed out in their review of the original 405:

“This is something we don’t see too often: an entirely new approach to power amplifier design. As Quad points out in its literature for the 405, class-A operation of transistors provides the lowest distortion, but drastically limits the amount of power an output transistor can deliver without overheating. (Most transistor amps use class-AB output operation, in which each of a pair of power transistors handles part of each signal cycle and shuts down during the other part.

Imperfect synchronism between the two halves causes the familiar “crossover distortion,” which accounts for most solid-state sound. In class-A operation, each output transistor draws current though the entirety of each signal cycle, eliminating the crossover transition but doubling the amount of time current is drawn, and thus tending to cause the transistor to heat up more.)

In “current dumping,” a low-powered, low-distortion class-A amplifier is used to control the amount of current passing through a pair of heavy-duty “dumping” transistors, and it is the latter which provide the driving power (100Wpc) for the speakers.”

Stereophile didn’t particularly like the original 405, but they reviewed the 405-2 much more favourably. Keep in mind that the Quad 405 is about as far away from typical US amplifiers of the time as one could get. It’s unlike any other power amplifier from that era.

Elegant Design

The Quad 405 and 405-2 are compact, measuring just 115 x 340.5 x 195mm. At 9kg, this is a small, dense amplifier, heavy for its size. The 405 is able to deliver 100 watts per channel, more than enough to drive most speakers. I can’t think of a commercially available amplifier that’s more compact, with fewer parts or with a simpler layout than the Quad 405. Tell me if you know of one.

The driver stage consists of two TO-220 devices operating in class-A. The output stage utilises two identical N-channel TO-3 devices, per channel. The driver stage is of very high quality, the output amp is the ‘current dumper’ and is a less precise, more robust unit operating in class-B.

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This is one entire amplifier channel. Note that there are literally around 50 parts, per channel.

The driver and output transistors are thermally coupled to one block of aluminium. Everything is board-mounted, there’s almost no wiring. The assembly forms one amplifier module, there are two modules per chassis. This is evident in the images above and below.

Thermal coupling helps lower distortion and the design as a whole minimises wiring and maximises serviceability. It really is genius in terms of packaging and miniaturisation at a time before SMD manufacturing.

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Notice how compact the amplifier modules are, each one roughly the size of your hand.

The two amplifier modules make up virtually all the electronics in a 405 / 405-2. Other elements include a superb-quality potted transformer, two 10,000uF filter capacitors, a diode bridge, some power supply wiring, a large front-mounted heatsink and some sockets. As a repairer, the Quad 405 series amplifiers are just about the easiest to service if you know what you are doing.

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The entire amplifier consists of the chassis, power transformer, two filter capacitors and two amplifier boards. The whole thing comes completely apart in minutes.

405-2 Specifications (Courtesy Hi-Fi Engine)

  • Power output: 100 watts per channel into 8Ω
  • Frequency response: 20Hz to 20kHz
  • Total harmonic distortion: 0.05%
  • Input sensitivity: 0.5V
  • Signal to noise ratio: 96dB
  • Speaker load impedance: 4Ω to 16Ω
  • Dimensions: 115 x 340.5 x 195mm
  • Weight: 9kg

Effortless Sound

Quantifying sound quality isn’t easy but let’s get this out of the way – the Quad 405 and 405-2 are beautiful sounding amplifiers and amongst my favourite solid-state designs. They aren’t the best at any one thing, but what they do well, they do very well. From the moment you hear one you’ll enjoy relaxed, effortless and fatigue-free listening.

Overall, the Quad 405 errs on the warmer, mellower side. A 405 adds little in terms of distortion, something you’ll hear in the relaxed flow of music and long periods of fatigue-free listening possible with one. If you find a 405 that doesn’t sound smooth, there’s something wrong with it or with another part of your system.

I work on plenty of 405s and 405-2s and whenever I test one, I’m taken by how incredibly sweet they sound. The lack of glare is noticeable and unusual with solid-state gear. But, as might be expected, original units can sound tired, ‘hummy’ and in general need of TLC at this age.

This is going too far, but you probably understand what I mean!

Mellow..?

Some describe the 405 as sounding rolled off, but I disagree. To me, these amplifiers sound smooth and lack that edgy quality of many transistor amplifiers. Measurements don’t support the claim of a rolled off top-end, but it’s not a fast, wide-bandwidth amplifier by any means. It’s also unlikely to blow up like one either!

Bass is clean and rich. It lacks the last word in slam and authority. If anything, it’s the bass that’s rolled off to my ears and keep in mind that these amplifiers are capacitor coupled at the input, so they do have an input filter. There’s no ‘bass bloom’ here to flatter small speakers though, just clean, accurate bass. Remember, this amp has just one pair of output devices per channel, so the most current hungry speakers are going to stretch these diminutive amps.

The midrange is warm, resolved and three-dimensional with good source material. This is definitely a strength of the 405-2, like a good valve amplifier perhaps. Sound staging works to enhance this feeling of three-dimensional realism and pinpoint imaging. Treble is smooth, never etched or bright. What a welcome antidote to the bright and even painful amplifiers out there.

Overall, a good, fresh Quad 405 or 405-2 is a beautiful sounding amplifier. My only criticisms are a slight lack of sparkle, air and deep bass compared with the very best. These audible traits separate the 405 and 405-2 from the very best I’ve heard in my listening room, like the Perreaux PMF-5150B, Krell KSA-150 and BAT VK-500. These limitations are dramatically reduced however with a series of improvements that I implement in these amplifiers.

Quad 405 Serviceability

The Quad 405 is an easy amplifier to work on compared to most. The whole unit can be completely apart and broken down to board level in minutes. You can even remove the side panels and work on a module whilst it’s still bolted to the chassis. Check out some of my Quad 405 work here and here.

Quad 405-2
Here’s a customer Quad 405-2 with modules out, ready for a complete overhaul and a full series of improvements.

All electronic parts are replaceable with modern equivalents, but original factory parts quality is very high. The only issue that is the 405-2 current limiting sub-boards are no longer available, but even this is no real problem. You can remove them altogether if you like to operate with no protection, the amp will work fine without them. Better still, they’ve been reverse engineered and are available from Dada Electronics for example.

Furthermore, the popularity of the Quad 405 and 405-2 has spurred the development of a range of modern replacement modules. Some are rubbish, like these cheap Chinese boards found on eBay for example. But others look amazing, like the NET Audio 405-3 boards, unfortunately no longer available. I had a customer who owned two ‘405-3’ amplifiers contact me and we chatted for a while about how good these modules sounded! More on what they sound like here.

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NET Audio 405-3 board. Now THAT’S a nice board, even though it’s not a Quad original.

Clones & Knock-Offs

I’m often asked about the cheap boards and 405 clones found on eBay and elsewhere. Check the comments and you’ll see I’ve had long discussions with readers about this. Understandably, many will have questions, especially those with limited experience working on electronics, owning and listening to a range of good audio gear.

First off, I’ll never understand trying to save just almost nothing on something that’s already a bargain. Let me draw a parallel with replica watches. Just like a real Rolex or Omega, a real Quad 405 contains premium quality genuine parts rather than cheap fakes. All the original electronic and mechanical parts are of very high quality and all contribute to the sound. The clones use the lowest grade re-labelled and fake parts.

Fake Quad 405
These nasty looking Brezze (Breeze..?) Audio Quad 405 boards are fairly typical of what’s out there. I advise you to save your money and put it towards a real Quad 405. This is from the perspective of a specialist who doesn’t have either product to sell you. Think about that.

“But Mike, they are Quad 405 boards, it says so..!”

No, they definitely aren’t. Look, I can wear a badge that says I’m Brad Pitt, and I’m still not, unfortunately.

Did you know that the superb original potted transformer makes a big contribution to the sound? Clones often use cheap toroidal transformers wound with sorry that’s not real copper and will not sound anything like the original, for this reason alone. Don’t even get me started on semiconductors and how important they are.

China is the number one source of counterfeit semiconductors and most are simply rebadged, cheap parts made to look vintage that are clones or copies of other well-known parts. Real On Semi 15024 devices are $10 – $20 each, depending on how many you buy. Do the math and figure out how each board can sell for $40 with way more than $40 worth of ‘real’ parts on it. Anyone..? Bueller..?!

A real Quad 405 or 405 board contains the actual DNA and parts specified in the original design. Replicas have redrawn boards, circuit changes, and cheap board material, populated with the aforementioned fake parts. They have no performance guarantees and are built and sold by people cashing in on the desirability of the original product and on buyers looking to find a ‘bargain’.

Confirmation Bias

If you’re looking to buy a clone, you are likely inexperienced, hunting for a bargain and probably haven’t heard a real 405 or 405-2, so the replica watch comparison is a good one.

But Mike, I’ve read the reviews of people who’ve bought these, they love them!

Look harder, definitely not all of them.

There’s something called confirmation bias which virtually ensures that you’ll read positive reviews from people who’ve convinced themselves that these are great value. These reviews are written early and can’t be changed later, when the amplifier fails, the reviewer hears a real Quad 405 and the ‘value drunkenness’ wears off.

A lack of experience means that, for many, a clone may actually be the best amplifier they owned. It may even be the only amplifier, further reducing the credibility of such reviews.

Would you wear a fake Rolex? Do you think a ‘clone’, with a crappy imitation case, heatsink and fake parts is good value when you can get a real one for around the same money? If you answered yes, buy a clone, but don’t call it a bargain, just call it what it is – a low-quality knock-off of one of the great amplifiers, for not much less than the real thing.

For everyone else, I assure you that clones, replicas and counterfeit parts are just a waste of money, for the same reason fake watches are. A real Quad 405 or 405-2, made in England, is a genuine hi-fi bargain, often selling for only a few hundred bucks. These amplifiers still represent the ultimate high-value hi-fi, despite people waking up to them.

Buy the real thing. You’ll be helping not fund the production of counterfeits and ripoffs and you’ll also have the real sound of the lovely Quad 405 / 405-2. Invest in having it professionally overhauled and you’ll have a low-cost, high-value friend for life.

System Matching

People also often ask me questions about “what would go best with this” and so on. For a long time, I ran my Quad 405-2 with a pair of Yamaha NS-1000M monitors. This is an excellent match, the slightly mellower sound of the Quad 405-2 is a great partner to the airy clarity of the wonderful NS-1000.

Many will also be aware of the legendary Quad electrostatic speakers like the ESL-57 and later ESL-63. Quad designed the 405 and 405-2 to run these speakers, so this is also an excellent match, though as a commenter pointed out, the ESL-57 can be too tough a load for many amps, so the 405 and 405-2 are definitely better with the ESL-63.

As a general rule, the 405 and 405/2 lack really deep, tight bass though, so don’t expect one to drive your Infinity Kappas, it just won’t work. The Quad is better suited to small to medium-sized speakers of moderate sensitivity.

Overhaul & Upgrade

Unimproved Quad 405s and 405-2s currently sell for around $500 – 750 AUD. They would be a deal even at $1500, so they are a fabulous buy for less. Seriously, what else can you get that sounds this good for 500 bucks? The best thing is the understatement of these lovely amplifiers, like fine pieces of 1950’s English industrial art.

It’s a very good idea to have your 405 or 405-2 overhauled if it hasn’t been. Many are running original capacitors and parts, a testament to their durability, but they can be dramatically improved. This is something I’ve been doing now for a while now, with great results. I have a series of improvements I can apply to your 405 or 405-2, developed, tested and implemented for various customers, and in my own 405-2 of course. The sonic benefits are not subtle, turning this already great-sounding amp into a serious heavy hitter.

A full restoration is an even better idea, part of the complete overhaul and upgrade process I’ve developed for these amplifiers. This includes output matched devices, thermal pads, op-amps, special MIL-spec silver mica, polystyrene and polypropylene capacitors, various premium electrolytic capacitors, new lab-grade power supply caps and more. Everything has been carefully chosen and tested for the best results.

Quad 405 2 Filter Capacitor Premium Upgrade scaled 1
This is our filter capacitor upgrade installation, featuring uprated, lab-grade filter capacitors with an ultra-premium film bypass package. Note the neat installation, retention of original looming, solder tags and so on.
Quad 405-2
And here’s another more recent example of my work on a customer’s 405-2. Premium high-C power supply upgrade in this case, without the film bypass arrangement.
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This on the other hand is how not to ‘improve’ a 405 power supply

I’ve had customers ask if it’s worth upgrading a 405 or 405-2. Consider that to replace a 405 or 405-2 with something decent but that probably won’t sound as good, will cost $5000 AUD or more. With this in mind, spending a few hundred dollars to refresh and seriously improve your Quad is one of the great no-brainers in hi-fi!

Have a go if you know what you are doing, but if you don’t, spend the money and have the work expertly done. I’ve seen too many of these amps where people have fiddled and caused problems. Consider what could you be doing to earn money while an expert works on your amplifiers instead! If in doubt, look at the 405 above.

Further Reading

The Stereophile reviews of the 405 and 405-2 are good places to start to get your head around what people were thinking when these amplifiers were released. I’ve written a lot more about the Quad 405, including several pieces about restoration, modifications and upgrades, and servicing. Positive Feedback has a great piece, with lots of mods and other technical details. Yet another page lists more modifications and upgrades.

One of my favourite resources is Keith Snook’s fantastic Quad repository. Keith goes into detail about his own journey with the 405 and breaks things down over two large and very detailed pages. The first covers the original 405 and its various iterations, the second covers the 405-2.

The Bottom Line

If you are looking for an amp to soothe the soul, I encourage you to listen to a Quad 405 or 405-2. Better still, just grab yourself one to play with on a rainy day, you won’t regret it. For the price you’ll pay for the genuine article, you simply cannot go wrong.

If you already own a Quad 405 or 405-2  and you’d like me to service, overhaul or improve it for you, visit our Contact page to get in touch.

If you enjoyed this article or maybe it’s helped you choose a Quad 405, you’re very welcome to say thanks by buying me a drink via the donate button!  🙏



Quad 405-2 Power Amplifier

$500 - $1500AUD
8.8

Chassis / Build-Quality

9.5/10

Features

6.0/10

Sound Quality

8.5/10

Serviceability

10.0/10

Bang-Per-Buck

10.0/10

Pros

  • Superb build and parts quality
  • Smooth, relaxed, refined sound
  • Ease of service, high reliability
  • Tiny for the level of performance
  • Multi-voltage

Cons

  • Deep bass and air slightly lacking
  • DIN connectors and no power switch
  • Capacitor coupling non-DC design

41 thoughts on “Quad 405/405-2 Power Amplifier Review”

  1. Interesting article. Why do you think that the Chinese boards are rubbish? Looking at the circuit diagram for the 405, it’s pretty basic and the component cost won’t be a lot. With modern cad I would expect a better pcb layout to be achieved than the original along with better modern components than the original. Have you actually tried the copies to justify the comment? I’m asking as I’m looking at makin a modern ‘copy’ but adding a streaming server to it.

    1. Hi Richard, thanks for leaving a comment and I’ll elaborate on a couple of points here that hopefully will help.

      Have a good look around my site and you’ll see that I’m interested in helping people make smarter, more informed choices, by sharing some of the work I do here @ Liquid Audio. If I don’t have first-hand, factual information about something, I generally won’t comment on it. If only more people shared this philosophy! 🙂

      With that in mind, yes I’ve seen some of the Chinese Quad boards and they were of poor quality, hence my comment. Some I’ve seen are not copies, hence you are not getting a 405, and board quality was poor. I haven’t seen all of them of course, there may be some good copies. Sadly, most cheap Chinese hi-fi and audio boards are of low quality.

      Regarding parts, no, modern parts are not automatically better. Some modern parts are better, some are worse and the commonly available Chinese parts are usually terrible, especially capacitors and semiconductors. There are tiers or grades of parts too, with vintage and modern parts. With Chinese kits, there is no QA in terms of what you’re getting, no way of knowing if the CAD layout is better, it could be worse.

      The folks buying this stuff are generally not in a position to make informed observations regarding these points either. There are so many terrible fake semiconductors and caps out there now from China that many professionals won’t buy them at all, myself included. I only trust the QA and supply line QC of large commercial vendors like Mouser Digikey etc.

      So, with these things in mind, I can’t see the point of knock-off boards/amps when you can buy a real Quad 405, with superb original boards, transformer, case, parts and pedigree, for a few hundred bucks. There are (sorry, were) of course the Net Audio ‘mk 3’ boards, they look good, haven’t heard them though.

      In my opinion, there is only one path to follow with classic audio gear that’s to get the real deal. It’s all about the history, the pedigree, and the fact that it sounds the way it does because of the layout and the parts.

      Anyway, hope this helped!

    1. Hi, any high-quality, transparent preamp will work with a high-quality power amp like the 405. Obviously, synergy with the rest of your system and room is very important here, so you’d need to consider this. The 405 can be bridged and run as a mono amp, but realistically, there’s plenty of power there with the 100 Watts a side available with a single amp. It would certainly be interesting to try though!

  2. I’ve found that the Schiit Saga is fantastic in front of the Quad 405 with a RCA Black Plate tube in there. I’ve never heard more life like sound reproduction. The 405 is magic with Aurum Cantus F620 speakers (4 ohm).

  3. I too am curious about the Chinese 405 Clone boards. As recently as 2006 I was still able to source rebuilt boards from Quad Electronics (International Audio Group) directly from their Huntingdon address for about $90, but I don’t know whether they offer this service anymore.

    Instead I can buy a pair of boards for $50-$60 including shipping from China, such as this listing from Douk Audio: https://www.ebay.com/itm/Douk-Audio-QUAD405-Power-Amplifier-2-0-Channel-MJ15024-Hi-Fi-Amp-Assembled-Board/251715936179

    The other options are: spend a few weekends troubleshooting, repairing, and recalibrating the blown board myself or spend $200+ on a replacement or a professional repair.

    Have you measured or listened to any recent Clone boards? Thanks for any feedback!

    1. Hi Ralph, thanks for your question and I realise there are a lot of misunderstandings around cloned boards. I’ve covered some of this in a previous answer but I’ve elaborated here on a couple of important points, I hope it helps.

      Yes, I have looked at some 405 clone boards and no, I cannot recommend them as a general rule. No, I’ve not seen all of them and no, I’ve not measured any clone 405 boards. I choose not to work on cloned stuff from China, read on to find out why.

      Consumer-grade Chinese boards contain generally low-grade parts of unknown specification and performance, in most cases non-genuine or fake semiconductors and are generally unqualified and of unknown performance. Clones often contain circuit changes that mean they aren’t even clones. It’s very simple, you’ll end up with an amp that isn’t a Quad 405, with unknown performance characteristics, and it’s probably not even cheaper overall!

      The original boards are well designed, easy to work on and repair, contain excellent parts of known quality, meet known performance specifications and are the real deal historically and electrically. I guess we each have to decide which elements of that are important to us. For me, originality, parts quality and verified performance are critically important.

      I completely understand that this isn’t the answer many want to hear, but it comes down to getting what you pay for. The same can be said for fake watches. At first glance, they appear very similar but dig deeper and there is a world of difference between a fake and the real thing. The devil really is in the detail.

      I mention fakes for good reason. Genuine MJ15024 output devices are around $10 each, from trusted vendors. Does this $50 purchase really contain $40 worth of genuine MJ15024 transistors? What about the cost of all the other parts, aluminium, shipping..? The BOM for these boards using genuine and known-brand parts would come to $100+. When you do some math, you’ll realise that something is amiss.

      Fake semis are highly problematic and exceptionally common in cheap Chinese gear. When one dies, you relace it with perhaps a genuine semi, and no longer have a matched pair, because the fake used a different die. This causes circuit instability and round and round you go. You always want genuine semiconductors, without exception, so I would be replacing every transistor in one of these kits with the real thing, further adding to the cost.

      Now I’m not saying don’t try to build one of these, by all means go for it, but realise what you are, and are not getting. Also realise how inexpensive the genuine article is. When you add in the cost of boards, transformer, case, wiring, connectors and time, I can’t see the value in a clone.

      Anyway, I hope this helps and don’t hesitate to let me know if you have other questions.

  4. Lars A Gronningsater

    Hello, thanx for your review.
    On the cons list, I would add bad protection from electrostatic shock.
    I touched mine with our hoover and the main amps blew .
    It’s happened twice to me. I guess I was not careful enough, or I forgot to use an outlet with ground.
    Now I’ve switched to Japanese gear that doesn’t need or have a grounded mains.
    Now I’m thinking of selling mine with the Quad 33 pre-amp or upgrade both with new parts and phono connectors.
    Cheers!

    1. Hi Lars, thank you for your kind words and comments. The 405 and 405-2 are earthed by design and superbly engineered in every sense, including safety. Going a step further, the schematics of every version show that chassis earth is part of the design, so the fault you’ve described shouldn’t actually be possible with an unmolested 405 or 405-2 and a properly earthed mains cable and mains outlet. Many 405s and 405-2s I come across have been messed with and have reduced performance and safety as a result of poorly thought out and implemented modifications. This may be part of the story, or maybe there is something else going on there with the vacuum, wiring, mains outlet or amplifier.

  5. Thanks for the detailed answer. Since the time I asked this I built a DIY tube amp and also ordered a class A headphone amp from the Breeze Audio site on Aliexpress, and was pretty impressed by the parts quality. I think there exist vendors in China who are deeply enthusiastic about audio and use high quality components, servicing both the local audio community as well as hobbyists in Europe, Asia, and the Americas. In some cases this means cloning classic gear which is otherwise not available new anymore, at very reasonable prices. I’m sure there are also scams, but I suspect these are less likely with the established vendors who have reputations to protect. I also don’t think China has a monopoly on scams!

    1. Hi Ralph, no problem and my apologies as I don’t recall your original message, nor could I find it quickly. No, China definitely doesn’t have a monopoly on scams, but a huge volume of hi-fi ‘junk’ does originate in China, unfortunately. The other issue is that most end-users, hobbyists etc, for various reasons, are unable to distinguish between fake and real parts. Many capacitors supplied with Chinese kits, for example, look like the real Nichicon MUSE, Elna Silmic etc, when they are in fact fake parts with far inferior performance. The same is true of many semiconductors and only careful testing or destructive analysis can determine the non-genuine nature and sub-standard specs of these knock-offs. Having said all of that, there is a smaller proportion of good gear from China, some of it really good, though it tends not to be the cheap stuff. The fake parts problem is pervasive and a very real problem, but I’m glad you’ve had some success with the kits you’ve built.

  6. Hi Mike just wanting to know if you can recommend a service centre in Sydney for my Quad system.
    I run a 44 preamp with bridged 405s and Quad 66 CD Player into Kef Corelli speakers.

    Its approx 30+ years old now and still sounds amazing but would like to see what updates are available for all units.
    Thanks.
    Brian.

    1. Hi Brian, great system! Unfortunately I can’t recommend any one over there. I’ve only dealt with customers who’ve had bad experiences on the east coast with things like this. Most service centres don’t offer improvements either, they tend to provide basic parts or board replacement services. Feel free to call to discuss!

  7. Thanks for the info what’s the best number and time to contact you on?
    It still runs well considering its age, got to admire British quality! so any thoughts you have would be appreciated.

  8. I have two Quad 405s. The first is a 405-2 that I bought in 1984. It has been completely reliable over its 37 year lifespan and has never been touched internally. The second is a 405 made in the 70s that I inherited from my father. It too has been totally reliable in my ownership although there is a sticker inside indicating that it was serviced sometime in, I think, the 80s by Quad in the UK.

    Both these amplifiers have traveled the world with me. Unfortunately the older amplifier suffered some water damage when it traveled as sea cargo. It has been refinished a Toyota metallic black by a local car paint shop (it was what they had!). It looks fine but I prefer the original finish. At the same time I replaced the boards with the latest available 405-2 boards.

    Both amplifiers are in regular use. As I have more amplifiers than I need I alternate the two 405s.

    As has been noted these are superb well built amplifiers and you can listen to them for hours on end without getting tired of them. The 405-2 I bought in 1984 is probably one of the best bang for buck purchases in my lifetime.

  9. Hi! Really enjoyed this article. When I was a broke, young 2-something back in the late 80’s I was able to charge my first entry-audiophile system with a Quad 405-2 driving Vandersteen 1-B’s and it was the most amazing setup I ever heard. I was so pleased with it. I had to part with the Quad a few years later and have mourned it ever since. Now I’ve just purchased an original 405 refurbished, (hopefully well, haven’t received it yet) and will be driving a pair of NHT 3-C’s with it. Of course, after ordering I read up on the 405-2’s better performance driving lower impedances, and was wondering how the old 405 might do with a 6-ohm load. Ironically, my other good bookshelf speakers, an old pair of PSB’s are also 6 ohm, which is obviously comparatively rare for home audio. Have you or any readers had experience with a 405 driving a 6-ohm load? Just curious 🙂

    1. Hi Jeffrey, glad you enjoyed the article. The 405 is fine with 8 ohm loads and possibly lower, but the 405-2 is better where more current is needed. This is all technically speaking of course, in reality, you can drive 6 ohm rated speakers with a 405 and it will work just fine, just not quite as well as a 405-2. What that translates to in sonic terms is a little less grip and authority. Hopefully, your 405 has been well refurbished, as many are not.

  10. I also use a Schiit Sega preamp with my Quad 405-2 power amp and I’m very happy with this combination. My setup is the solid state Schiit Sega which is longer available.
    I have also tried it with a Tube preamp but found this combination to be a little bit too rolled off at higher frequency. The more neutral Sega is a much better match.

    1. Thanks James, the Saga (not Sega) should work well. I’ve used the better sounding Freya with a 405-2 and it’s a nice preamp. Clean, neutral preamps like these will work well with the 405 and 405-2.

  11. I have the matched pre amp and original 405, linn cable and castle severn with monacor yellow drivers set up in my daughter’s bedroom either side of the bed crammed into the corners and despite such a poor set up the sound staging is still very good and I can sit there for hours listening to cds via a classic rotel. A sin I know but very rewarding.

  12. How do you think the 405 would be driving a pair of JBL 4333?
    Also, I would want to find a suitable pre-amp that has a good phono section and a remote. Any suggestions?

    1. Hi Gary, I’m sure the 405 would do well in this role, but there will of course be better options. For specific advice, I suggest you visit my contact page as noted in the comment header and submit your question with a few more details there!

  13. CHRISTOPHER J MALONE

    Hi Mike, I have two 405’s and a pair of mono Mod Squad 405’s, all of which need servicing. Being in the US, round trip shipping alone would $600-$800 for the set. After reading your article I would prefer to send them your way, but overall cost is a consideration. Do you recommend anyone in the States (I’m in N. California) that might be worth contacting?
    One other question if I might. When mono strapping these amps, I heard that there were two configurations. One would take the 100/w stereo amp and give you a 100/mono amp with high current capability for low impedance loads and the other would give you a much higher wattage rating into an 8 ohm load, but not suitable for lower impedance loads. Almost like a series/parallel comparison when hooking up speakers. Is this true, and do you know how McCormick (Mod Squad) used to do it? Thanks in advance, Chris

    1. Hi Chris, thanks for your questions. Shipping to Aus would certainly be expensive and I’d rather you didn’t send them all this way. I don’t know anyone in the states doing this sort of work I can recommend. That doesn’t mean there aren’t people doing it, it’s just a case of finding them and making sure they do the work well, rather than just doing work on Quad, and there is a very big difference from what I’ve seen first-hand.

      The two mono configurations make sense given the internal layout of the 405 and voltage limiting option, but I cannot comment on how others have implemented these configurations as I don’t have that information.

  14. Hi Mike. Is there anything that can be modified to have a deeper bass? At lower volume the bass is lacking the punch. At first I thought that the speakers are the problem, but it seems not. Mids and highs cover the bass by a high margin at low volume. Is it ok to use an equalizer (like APO) and increase the amplitude for bass frequencies ? Will that damage in anyway the amplifier? What do you think?

    1. Hi, thanks for your question. Yes, I offer a series of improvements that extend performance in all areas, with customers typically reporting that they find the bass to be significantly improved. I generally don’t recommend equalisation, this usually indicates the need to attend to other problems like room issues, system composition/improvement and listening habits. EQing bass can be risky, so use it with caution. Amps and speakers can be damaged due to exceeding the power envelope (clipping) or driver excursion limits.

        1. No problem! Unfortunately no, I don’t offer kits, instructions, schems etc, equipment needs to come here for work. This eliminates QC issues and allows me to keep what I’ve developed in-house.

  15. Hello Mike.
    I grabbed a 405 at a local thrift shop today for 100 Euros…. Haven’t tested it yet as I need a 4 pin DIN to RCA lead first… So no clue if it works 🙂
    The power light gets on at least. But good thing is a 100% refund if it doesn’t work….
    I want to use it with my old Spendor BC1s, and i hope that will be a good match.
    What is your opinion about using a cheap modern preamp with it ? I was thinking about something like the Pro-ject Maia Pre Box….

    1. Hi Steinar, great work getting the worlds greatest hi-fi bargain there! For 100 Euros I’d be keeping it whether it works or not and having it properly overhauled. Use it with the best sounding preamp you can afford. Doesn’t matter so much if it’s old or new, it just needs to be good. I can’t find any info on a Maia preamp but a lot of this type of gear tends to be filled with digital, bluetooth etc and sounds ordinary, so be careful there.

  16. Scott Falconberry

    Hi, proud owner of a 405-2! Works great except one of the banana jacks broke. I would like to replace it, but cannot find a suitable female jack. My 405-2 has small jacks. I suppose I could replace all four jacks but would rather not. Anyway, I don’t have the current/voltage specs for these jacks. Any idea what i can replace them with?
    I would live to send my unit to you but i live in the states.
    Thanks!

    1. Hi Scott, thanks for your question and glad you enjoyed the article! As you might imagine I receive a lot of enquiries like this and have a process for dealing with them. Technical queries like this may be submitted via the contact page, as noted in the comments header.

  17. Lovely review and proper credit to this fantastic amp. However unlike the ESL63, I wouldn’t drive the ESL-57 with a 405.. the dumping circuit doesn’t like the very low impedance and the tonal balance goes off the rails – plus you could do real damage. A transformer coupled amp or a Quad 33 is a much better option. I later ended up with a Beard P35 tube amp which was a real step up from the 33 and had good synergy with the 57.

    1. Thanks for your comments Eddie and really glad you enjoyed the article! The 57 is indeed a tough load, too tough for many amps, I’m glad you found the Beard a good match.

Hi! Feel free to share your thoughts and if you need advice, visit our contact page.

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