Net Audio Modified Quad 405-2 Amplifier

Net Audio Quad 405 Upgarde

Net Audio

Having recently accquired an second hand Quad 405-2 on Ebay, we were interested to see what improvements could be made to what already sounded fairly impressive.

Having already upgraded our 405 with heavy duty loudspeaker binding posts, teflon insulated phono sockets, and replaced the internal wiring loom with a combination of pure silver PFTE wire for input signal and silver plated PFTE for all the power supply wiring, we thought it time to send our amplifier boards off to David Pritchard of Net Audio to see what further improvement could be made.

The basic upgrade costs £50 and involves replacing old signal degrading electrolytic capacitors with Elna Starget type and upgrading the op-amp (typically a TL071) with a Burr Brown OPA604, and a few other tweaks here and there to really make the amp sing. Whilst David had the boards, we thought it worthwile to upgrade the output transistors as well (£35) and also purchase the Dual Mono Power Supply upgrade which we would fit once we got the boards back.

Ten days later the boards returned and we carefully fitted the new power supply which was a fairly straight forward job given the excellent instructions on the website and then reseated the amplifier boards.

David did stress that it would take at least a week for the new components to burn in and he was not wrong. Although the amp was evidently more detailed than before, it seemed somewhat sterile at first but after a week this had all but disappeared and we have to say the sound from this little amp has superseded all our expectations. In short for an outay in total of £400, we now have an amp that can compete with the best under £2000.

These amplifiers are built to last and the upgrade path that Net Audio offers further enhances their status as a classic piece of British Hi-Fi.

This entry was posted on Sunday April 2nd, 2006 at 7:04 PM and is filed under Amplifiers. You can follow any responses to this entry through the RSS 2.0 feed. Comments are now closed.

18 Responses to Net Audio Modified Quad 405-2 Amplifier

Steve b Says:
November 25th, 2006 at 9:21 PM

"David did stress that it would take at least a week for the new components to burn in and he was not wrong. Although the amp was evidently more detailed than before, it seemed somewhat sterile at first but after a week this had all but disappeared and we have to say the sound from this little amp has superseded all our expectations.

What changes occur in the components during this time to make the sound less "sterile"?

Hi-fi insight Says:
November 27th, 2006 at 10:42 AM


There was some really good information on the internet on why components such as capacitors (on of the main Quad 405 Upgrades) need time to burn. It was in relation to Black Gate Electrolytics but I am afraid I can no longer find it. There is some information on Wikipedia but there was more scientific documentation elsewhere.

It is odd that components behave in this manner but they just do. I have no scientific evidence on this thought but I also believe every other component in an electrical circuit effects every other one, so that a new component (such as a replacement capacitor) sounds different at first before the influence of the other components have had their effect on that particular one - hence influencing the overall sound.

If anyone else has any thoughts, then please feel free to comment.

Phil Says:
January 28th, 2008 at 3:52 PM

I'm sorry but you're talking rubbish. What 'beds in' after a week is your ears. And all this guff about silver PTFE wires - do you think they use this stuff in the recording studios? Of course not - they use 100s of meters of bog-standard copper wire to get the music onto CD. What difference is a few cm of expensive cable going to make? A big fat zero is what.

David mellor Says:
February 13th, 2008 at 9:03 AM

Well, that told him, didn't it?

David pritchard Says:
April 19th, 2008 at 10:14 PM

Dear All,

Out of interest the NET Audio - soon to be Quad Mod - 405 MK3 boards are now being manufactured. If Hi-Fi Insight would be interested in listening to a 405 MK3 amplifier for evaluation then I would be happy to post one to you for appraisal or/and the NET Audio 303 MK3 or Sonance MK3 DAC.

Many thanks for your past reviews - much appreciated.

Best regards


Harry denton Says:
January 12th, 2009 at 7:36 PM

I have been reading your 405-2 mods I am trying without luck to find 2 power transistors for my quad 405-2 can't seem to locate can you advise

Harry D
Deal, Kent England.

Keith snook Says:
March 26th, 2009 at 1:01 PM


I agree entirely - More people need to stand up and point out that the emperor has no cloths - There are both long term and short term adjustments made by the lump between the ears - This was clearly demonstrated by the BBC (and others) when it was established that A-B comparison of speakers and sound sources could not be relied upon - I wonder what takes longer for the brain to decide - Is it the sound is getting better with time ? or is it when do I tell the wife how much I have wasted on these little capacitors ?

regards to any one who actually reads these comments

Dr. venkmann Says:
July 8th, 2009 at 7:42 PM

Well put and well played. The human ear and psycho-acoustic phenomena are well understood by audiologists and a number of other science-based medical communities. Its too bad such nonsense is spouted. But there are many fools to fleece and they are short on education and long on voodoo-logic in most cases. It goes to show why the poor will never be rich. They are -- for the most part -- willing accomplices to being fleeced by audio charlatans who can convincingly spout pseudo-science to their eager and untutored ears.
Dr. P. Venkmann

Phil ii Says:
September 5th, 2009 at 12:53 AM

I have a pair of Quad 405-2's which have never been upgrade/degraded or mucked about with. They have been working perfectly since I bough them over 15 years ago.

there is SO much rubbish talked about this amp its unbelievable. Peter Walker and his team did "it". no one else did and thats what people cannot deal with. they never designed it and it gnaws at them. I borrowed a NET audio modified am, took it to my owm lab and tested it on a Ferrograph test set. Nothing new at all Sound wise NO DIFFERENCE WHATSOVER. So people save you money and just use vinyl and you will never hear better this lifetime. Mods cost £££'s those who do them sell them get it? Dont fall for their nonsense

Marc lewis Says:
September 12th, 2009 at 10:10 PM

Thought I would add my two pence worth by saying that Phil is indeed correct in saying that recording studios (where all your lovely audiophile recordings are made) on the whole, use 30a mains cable for wiring in monitors (speakers).

I know as I own and run a very successful studio here in the UK.

However, we run a great deal of vintage gear here (Quad 405 amplifiers included) and almost without question whenever we pick up a vintage unit it goes straight to our service engineer to be recapped (have all capacitors renewed) as these things do have a finite lifespan, typically around 10yrs.

The "emperors clothes" situation in the Hi-fi world has always made me chuckle... Tens of thousands of pounds on equipment and cables costing hundreds sitting in an acoustically untreated room is just laughable really, but upgrading components after time makes sense.

As for the bedding in period, I know this to be true of new monitors and speakers as they are electro-mechanical devices that do need to bed in, but I have never noticed any further improvement over time after receiving a re-capped piece of equipment.

Lorne gifford Says:
September 30th, 2009 at 11:18 PM

I have 1 x 405 and 2 x 405-2 running from a Quad pre-amp via 3 x graphic equalizers. Also a Quad tuner. I inherited this as part of a built in hi-fi system when I bought my house a few years ago. I'm finally getting around to sorting this out and was thinking about chucking it all and putting something new in, but after looking into it the Quad gear appears to be a bit of a favorite amongst those 'that know' about these things. Is it really worth upgrading these given that the rooms are by no means acoustically treated and my ears are similarly pretty standard.

Also, slightly off topic, but I've have a JBL control SB-1 subwoofer that has corroded (it sat next to a leaking conservatory wall). Could someone suggest a replacement that wouldn't mess up the sound, given that there's another SB-1 in the room.

Gary church Says:
December 23rd, 2009 at 9:36 AM

Replacing electrolytic caps after a period of time (maybe 10 years or more) is sound practice as they do dry out and eventually fail so that's good practice for a reliable operation in a studio. I suppose if the cap were near to failure it's impedance would increase and you may hear some effect of this. However in general, all this changing of components such as caps, resistors and wire is largely total old tosh. As one previous writer said what do you think studios are wired with. What are microphones, guitar pick-ups, speaker coils wired with? Plain old copper wire is the answer. This is also true of printed circuit boards and even the internal bond wires on integrated circuits so a few inches of silver plated, PTFE is just a waste of money.

As for things having to burn in I largely think this is the brain accepting the sound rather than anything changing. It also annoys me how the rest of the scientific world is happy to measure parameters with very sensitive instruments and yet the hi-fi looneys still claim to be able to hear things which no instrument can yet measure. And why do they rarely perform double-blind tests? The answer is that they would be exposed as frauds and be out of a job.

I used to be interested in hifi and read many of the magazines until one day I found some imbecile listening to coaxial digital cables and claiming more extended bass on some etc etc. It's a digital link - it will either work or not - that's it - it cannot affect the sound. I agree that jitter may have affect but that's to do with the player not the cable

My advice would be to replace the main electrolytics and then just listen to the thing. I ran some quads 405-2 for some years and for while in bridged mode and liked them. However I then essentially 'sold-out' and bought a Sony surround amp for home cinema use and actually thought it sounded better - more dynamic. I should really have done the double-blind test but I just decided to get on with life and enjoy the music

Rob Says:
January 2nd, 2010 at 11:20 PM

With the Netaudio 405 MK3 upgrade not only did the caps and other components get changed but the power supply was increased to double the capacity with the dual mono PSU mod included. This results in an amp that has a lot more welly than the original, current limited or not.

I later changed the op amps from the AD843 to the allegedly better Burr Brown OPA627s and was utterly delighted with the improvement. The sound is clearer, airier and more detailed.

There's certainly Quad mods worth doing and the Netaudio MK3 boards with DMPSU were a revelation to my system. Perhaps such benefits demand highly revealing speakers, a pair of which I am blessed with.

Thoroughly recommended.

Rass Says:
April 30th, 2010 at 8:43 AM

I have followed this thread with interest. I have been using a Quad 405-2 for the best part of thirty years and it desperately needs recaping. I am going to send it to Netaudio and get the Burr Browns, and I will let you know what I think. I am afraid I am not a silver plated PTFE man. The problem is that the new caps alone will transform it. But I feel I know the sound well as there is a difference according to the pre-amp ( I have only used two long term and I am confident that I can 'remember' the sound from each, I still have them and can check).
I guess I represent a huge constituency of amateur HiFi users, rather than enthusiasts, who just want a very good sound and do not believe themselves capable of discerning the possible very tiny improvements that may or may not emanate from some of the fancier tweaks. We have all seen what better speaker cable can do as you move from what is inadequate to the adequate, but I have to admit that personally I cannot find an advantage in going further than having enough copper to carry the signal, but that maybe due to other limitations in my set up. I am happy that I have found my level, but I do not denigrate those who push for more, it is rewarding hobby for them and without them we would never move on.

Bernasmeister Says:
May 7th, 2010 at 3:37 PM

I agree with Rass. If you can hear the difference then great, go on and enjoy it! I think it’s a waste of time to be arguing these things and not listening to what really matters: good sounding music!!! tweeked or not! (mine is!)

Danny Says:
August 24th, 2010 at 3:13 AM

Hi guys,the real justice is that maximum respect is to be given to all those genius of the original design :sorry!!the invention of the quad that has and is still giving a large majority of people great pleasure to date.However my first experience of quads capability was when I heard a 100% English man playing REGGEA music with a Quad 34/303 deliverd by vinal to power up a pair of Wharfdale E50 back in the late 1970,s.Those quads had no mods and they sound fine,so I went out and bought my self a 33/303,44 & 2x405,s 15 years later as soon as I could afford it.Thats the impact they had had on me ever since my first experience(just like first love).Reggae,jazz,soul or opera,they all sound good with the original quad specification.Nb..there is no harm with trying to improve the sound if it is posible..they will be till the good lord take me away from them. Good luck guys with the search for what you think is perfection.

Axtl Says:
October 28th, 2010 at 1:04 AM

I have also read this post with interest, and I paid particular attention to the fact that replacing electrolytic capacitors could alone transform the sound, as I have myself changed all the electrolytic capacitors on my 405 Mk I which led to a substantially different timbral balance.

Nigel Says:
July 9th, 2011 at 1:01 PM

I use a lot of Quad equipment. One of my systems is the 6 series with two 606 mk2's driving ESL63's and Gradient SW63's. All of my Quad I obtained second hand and had some units serviced by Quad in Huntingdon like a 303 two 44's a 405 and a pair of II's.
In my opinion I have heard many so called Quad upgrades from various companies and I heard no difference what so ever. I should say I'm 53 and had my hearing tested and was told it is excellent throughout the normal range. I have compared my systems to others costing many tens of thousands of pounds and really felt sorry for the owners of them! I normally listen to vinyl and own many turntables. After lots of testing all my systems are connected with very basic 2nd hand interconnects from companies like Chord but sound wonderful so why pay £100's? My speaker cables yet again are nothing special using 2nd hand QED silver anniversary mostly. (Of course I have 'burned them all in now'! KIDDING! ;) I too agree that non mechanical operating devices (like speakers as mentioned elsewhere) cannot change in time other than degrade of course in a way that can be heard by the human ear. What makes me laugh on top of what has already been mentioned is companies like Linn selling all their upgrades at such high prices and obviously there are a lot of people falling for it. I recently compared my Technics SP15 with a supposed superb Linn with every possible upgrade 'Val this and Sumani that' whatever I have no idea or wish to know what the parts were called just that my Technics sounded better in every respect and even the Linn owner (name witheld- he's so gullible he may try to by a Quad upgrade next!) agreed with me.
Quad's service returns the equipment to original factory spec. It doesn't cost much, normally £65-£70 including parts. My advice would be to take any Quad item direct to Quad for a service. You'll be more than happy with the results and your ears can't be wrong can they?

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