Quad 405-2 Modifications [Archive] - Audio & Video Forums


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Les Adams
09-24-2007, 01:34 AM
Does anybody have experience or knowledge of the best available modifications for the Quad 405-2 amplifier?

There are several companies offering mods, such as replacing the power caps, op amps and generally bringing the design up to date.

I like the Quad very much and it drives my Audio Vector M2's well, but in the never ending quest to make improvements (the budget does not extend to a new power amp), are the mods going to make a significant difference?

Also, does anyone recommend a particular company or service to carry them out?

Thank you in advance for any help in this matter, or any other suggestions as to how my system may be improved on a fairly tight budget!

Chas Underhay
09-24-2007, 05:22 AM
I've heard of several companies; Net Audio for one. I've also heard good reviews of the results but the reviewers have never made it clear whether they were comparing it with an amp that had recently been serviced and was within "factory specification" or an old one that was desperately in need a full service. Many components especially electrolytic capacitors do degrade over the years and this has an adverse effect on sound quality especially loss of bass.

I would think that if your 405-2 is more than ten years old and never been serviced you may be very impressd with the upgrade however, you may also be very impressed at the difference a full factory service can make.

Les Adams
09-24-2007, 03:23 PM
Thank you for your reply Chas.

You make a very good point. I do not know the exact age of my 405-2, except that it is one of the later versions with RCA inputs and relocated speaker terminals. I bought it on Ebay just over a year ago and all I can say is that it doesn't appear to be lacking in low frequency performance. It certainly out performs the amps in the Denon, which is why I use it. However, given that the model has been discontinued for some years, it is safe to assume a service may improve matters.

My thoughts are that if I am going to send it away, I want to find out first if the modifications like the ones Net audio offer will improve the amplifier over and above the original specification. If I liken it to my car, I can take it to BMW and they will service it... or I can take it to a tuning specialist that can make it perform even better!

So, to revise my question somewhat, Do the modifications such as replacing the standard op amp with a Burr Brown device and upgrading key components such as capacitors offer a significant improvement over a fully serviced, but standard, 405-2?

The companies that offer these modifications claim there is a significant improvement in definition, as well as the improved bass

Does anybody know if this is the case?

Chas Underhay
09-25-2007, 01:53 AM
Hi Les

Theoretically, there will be better quality components around than there were twenty five years ago which is about when your amp was introduced. However, Quad power amps have always been good. Over the years, there have probably been more Quad power amps used professionally than most others. I still use a 303 power amp but do keep it maintained by the factory.

I know what you are saying about tuning specialists but I sometimes wonder how these guys can think up "improvements" in their back street garage that BMW's R&D department couldn't come up with, with their £multi million budgets??? And how does it effect the guarantee?

The companies that do the modifications are bound to say that there will be a significant improvement, however, in Hi-Fi circles "significant" can often be to an ordinary mortal "inaudiable"

Why don't you talk to Quad's service department before you do anything, I've always found them to be helpfull.

I can also see from your posts that you are in possession of some nice classic kit and when it comes to classic; there is a lot to be said for keeping it "as issued"

Les Adams
09-25-2007, 02:07 AM
Hi again Chas,

As a matter of fact I spoke to Quad (AIG) this morning!

They are confident that a service will ensure the best from my 405-2 but conceed there are other "tune-up" sevices available that may offer improvements over the original design, such as up-rating the PSU by installing descreet supplies for each channel and replacing the standard op amp with a Burr Brown device.

The difficulty I am having is that they have not tested any of these "specialist" modifications and are therefore not in a position to comment or advise.

I am not too concerned about keeping the Quad original although I understand your sentiments. My Garrard 401 is original, but I put it in a very nice oak plinth to improve it! I would view the mods to the Quad as being much the same thing. Fot me it is about getting the best performance. I just don't want to be suckered in by clever claims and advertising by these "specialists"!

Chas Underhay
09-25-2007, 02:32 AM
Hi Les

I know there have been several companies over the years who have done upgrades to Quad amps but I definately don't know how "significant" or even audible the improvements really were.

My concern has always been that I know that Quad's service department have been around for a long time and can service all Quad amplifiers and I expect them to be around for a long time to come. However, I don't know if Quad can still service a "modified" amplifier. I also don't know if the companies that modify them now will still be around in five years time to service their work and I don't know if they provide sufficient data for them to be correctly serviced by others in the future.

There is a risk factor involved and I don't know whether any "improvements" would make that risk worth taking. As I said, my 303 is standard and I am happy with it.

It's your choice Mate!

Les Adams
09-25-2007, 10:24 AM
Hi Chas

Thank you again for injecting some common sense into the discussion!

It would indeed be a problem if Quad refused to repair a modified amplifier should the need arise in the future and that is a factor worth bearing in mind.

I think I will put another call in to Quad and ask them if there is an approved modification they can make, such as a superior op amp. It may be that such a device could be fitted as part of a service. As you rightly said, the quality of available components has improved sinse this amp was built and I suspect they will be using more modern components now anyway.

It might be worth while getting the amp to them to see if it is working to spec or if it is a bit tired and in need of an oil change!

I am also bearing in mind that this amp is powered up 24hrs a day as it is difficult to reach the rear mounted power switch. It is used every evening for the front L+R of the home theatre system and for stereo use every day to listen to the radio, plus a few "serious" stereo listening sessions a week so it has a few hours on the clock.

Chas Underhay
09-26-2007, 02:26 AM
Hi Les

Personally, I'd have the amp serviced; you obviously like it and servicing will only make it better not worse.

Whilst modern components may well "spec out" better than components of twenty five years ago; it doesn't mean you will be able to hear it. After all you would be lucky to get below 1% distortion from the very best cartridge or loudspeaker so it won't make any real audible difference if an op amp specs out at 0.01 or 0.001%.

It may be worthwhile for you to audition a Quad 909 because I doubt very much if the "back room mod boys" could get a Quad 405-2 up to 909 spec (not withstanding the extra power output). And to be honest, I doubt if you would really notice much difference between 405-2 and a 909 in your or any other system unless you needed the extra power.

Have you got the big power supply for your Dino? That will make a worthwhile difference!

Les Adams
09-26-2007, 02:51 AM
Hi Chas,

The more we talk, the more I am thinking that modifying the 405-2 is not such a good idea, especially as I am getting quite stunning results from it anyway. Maybe I should wait till funds permit a new completely different amp. The expression "throwing good money after bad" may not be wholly appropriate, but you can see where I am coming from.

I do not have the big PSU for the Dino.Does it really make that much difference?


Chas Underhay
09-26-2007, 03:42 AM
Hi Les

Well, as you are already getting quite stunning results from your 405-2; I would have said that answers your question.

I don't know how much you use your record player but if you want to chase the audio holy grail; an SME Series IV (especially a factory silver wired one) will be a very noticable improvement over your 3009. A quality mc cartridge such as an Ortofon Kontrapunct b will be an improvement over your V15 and yes. the big power supply does make a worthwhile improvement. My only reservation would be that it may be less noticable with your movimg magnet cartridge than a much lower output moving coil. I have a Trichord Delphini Mk2 which I bought with the small PSU a few years ago. When I first used it I was bowled over by the clarity, detail and the low noise level (like totally silent even on full volume). However, after about a year I started thinking that although I would never have gone back, it didn't seem to sound quite as warm and gutsy as before. I then bought the big HR PSU and never looked back again.

Your 405-2 is already a very good amplifier and the difference between that and the perceived very, very best is going to be very small compared with the differences that can be made with upgrading the front end and speakers.

09-26-2007, 07:44 AM
Well I was going to chime in, but it looks like you guys have everything under control.
BTW the Quad is one hell of a good Amp. If it were me, I would just have it serviced.I did this for my GAS, and it sounds sweet.

Les Adams
09-28-2007, 03:59 PM
Hi Mike and hello again Chas,

There has been a change of plan! :rolleyes5:

On Wednesday I went to my local Hi-Fi dealer from where I purchased my Audiovector loudspeakers. They are also main agents for Quad and I spoke to them about getting my 405-2 serviced. I was also curious to see how a Quad 909 would sound driving my M2's - this was something you suggested earlier Chas and I am glad you did! I have a good long standing relationship with this dealer so I asked if I could borrow one to try but at almost £900 I had it in my mind that it would be an interesting experiment only! ......However.... They offered me a very good deal so I borrowed it and WOW! What a difference! - and what a fantastic amplifier! The bottom end is far more controlled and deeper, midrange clarity and definition is stunning and the top end sparkles - cymbals and hi-hats have a realism about them that I have not heard before. I am also hearing far more detail in recordings I have played many times before. Overall, the whole sound is more dynamic and controlled.

As you commented earlier Chas, I also doubt that even a full service or having modifications performed would ever make my 405-2 sound this good. You might guess from my enthusiasm that the 909 will not be going back to the store and my 405-2 will soon be appearing on Ebay!

I take on board your comments about my turntable setup, but I think upgrading it in the way you suggest is going to stretch available funds too far. I must say I have been very impressed by the Shure cartridge and the whole Garrard / SME S2 / V15Vxmr combination is such a tried and tested formula that I am going to stick with it for some time. I may however ask the dealer if I can borrow one of the big Trichord PSU units to see if it makes a worthwhile difference in my setup.

I am also very (very) happy with the Audiovector M2 speakers (Denmarks secret I call them). Any slight shortcomings I thought they had in deep bass definition and midrange clarity have been sorted completely by the new Quad amp.

I realize this system is still modest by comparison to some of the real "holy grail" stuff out there and there is always something better to be had, but right now, this system makes me smile :wink5: every time I play it and involves me deeply in the music which, when all is said and done is what it is all about!

Chas Underhay
09-30-2007, 01:22 PM
Congratulations Les! you sound like a very happy man. If you can get close to getting your money back on the old 405-2 that will be a mega result. I still think you would have been impressed with the results of a thorough factory service for your old amp but your new 909 has got to be a first class investment. It will outlast you even if you are only 25 but in ten years time; do send it in for a service before you start auditioning for an upgrade.

Your Garrard 401 / SME 3009 / Shure V15 is a first class set up and was "world class" a few year ago; a very classic combination. I wouldn't mind betting it still sounds bl00dy wonderful. The point I was trying to make is that the difference between an already very good amplifier (if working correctly to spec) and an even better amplifier is not normally anything like as noticable as the difference between a very good cartridge and an even better cartridge. The arm and cartridge I mentioned would be more acurate than what you have but wouldn't necessarilly sound any "nicer". It was just that you were enquiring about making improvements.

Anyway, all the best and happy listening.

Les Adams
09-30-2007, 11:58 PM
Hi Chas,

Yes I am very happy now!

I guess I will never know just how much difference the service to the 405-2 would have made, maybe I would have been happy, but having tried the 909 and got such a marked improvement I decided not to take the risk. Had I paid out for a service only to find it wasn't quite up to the performance of the 909 I would have kicked myself.

As you rightly say, the 909 will be my amplifier for years to come now, unless I win the lottery!

Thanks again for your comments and advice, it was all very welcome and understood.

Best wishes.