View Full Version : Vintage amps from Quad -70's/80's

10-07-2011, 09:34
Just joined the forum recently and have posted in the welcome section a few weeks. As stated in my intro in the welcome section I am looking to acquire a vintage/classic set up.
I have read a lot on here regarding amps and speakers from the various 'classic' British hi-fi manufacturers such as Quad, Leak, Naim, Linn, Celestion,Tannoys etc.....Wow there is so much to learn about the pros and cons of older equiment:scratch:
Here is the first of many questions that I will posting......
Looked at the Quad 33/303 combination and the other later models such as the 34/306,44/405.
The above are at least 30 years old and as such would be requiring servicing to bring it back to the sonic performanabce intended when they were new. How easy is it for a 'novice' to undertake such upgrade/service of the amps? I have basic soldering skill and can work my way round a schematic diagrams so hoping is a project I can do myself; this way I can learn about electronincs and carrying out simple repairs etc. It is more satisfying for me to 'tinker' the 'gear' you enjoy and like.
Oh before I get carry away with my soldering iron:lol:.........your thoughts on the 44/405 (my preferred choice) set up would be greatly appreciated.

10-07-2011, 10:53
The LATE 44 with phonos and chocolate coloured buttons was a good preamp, the earlier version inclined to be a bit too dry in sound with little in the way of reverb reproduction in my experience.

As for the 405, these need regular supply cap checks as the originals, and possibly most replacements, will only last ten to twelve years before leaking - I had two 405's with this problem and saw many more. As older ones are over thirty years old, you'll need to be careful. Fortunately, replacements are easy to obtain and re-manufactured boards can be got from Quad, as well as Dada Electronics. The latter supplier I've used and trust.

The older 33/303 can be transformed into charming vintage items, but need plenty of work, especially the 33, which CAN be fully updated I found. In stock form, the sonics can be variable depending on the condition of the individual units, ranging from "nice" to rough as a badgers backside. All stock 33/303's can sound tight-a*sed with iffy bass, but once the restoration starts, this bass quality can be removed and replaced with something more "expressive" and up to date. the cap coupling to the speakers remains, however.

My feelings towards the 34/306 are largely negative sadly. The former will need some possibly leaky caps looking at, the input impedance needs to be raised (the little resistor "flags" on the tape circuit) and the output level correspondingly raised. I heard one such modified and it was far better on digital sources, although limited in maximum output. As for the 306, IMO it's hopeless on percussive music, sounding flat and rather limp-wristed when compared to the others.

Hope this helps - just my impressions of course and others with different setups and musical tastes may feel different.

Buying old gear can be fraught with problems, as 1970's stuff is now pushing 40 years old. Solid state gear made in the UK back then didn't seem to have the longevity of certain components as the comparable far eastern products did and even these are starting to need attention now.

10-07-2011, 20:43
Thanks DSJR - you have given a good account of the QUAD amps based on your experience. I do understand that other may have different views based on their set up/musical taste and listening environment. I guess the choice of partnering speakers are also equally important when considering vintage gear.
What would be an ideal speaker brand to go with a 44/405?

12-07-2011, 11:09
Hello Peter

I would concur with Dave that the best of the Quad 44 preamps are the later versions: those having the two extra slopes on the ‘Tilt’ control of +/- 3dB and with the red ‘Cancel’ LED removed. The removal of the LED only amounted to a small sonic improvement (LEDs tend to be noisy), the greatest improvement came about through a complete redesign of the motherboard, which now included the muting relay. This change was implemented on samples with serial number > 12,000.

There were numerous small changes made to earlier versions but all were in place by s/n 12,000.

Regarding the Quad 405 power amp, I would suggest you try to get one of the later versions of the 405-2. If however you can only get hold of a 405-1 there are many small and easy changes that one can make to improve the performance. The most obvious is to change the op-amp to a better one. Companies like NET in the UK and Dada in Belgium are very helpful in this regard; both can be found on the web. (Both these companies provide upgrades to the 33/303 amplifiers as well.)

I would also advise replacing the current limiting resistors used with the output transistors with those of 1W rating; those fitted by Quad run close to their limit.

I have frequently read of the need to replace the power supply capacitors in elderly 405s. I have two Quad 405 power amps, one of which is a heavily modified 405-1. The modifications however have only been made to the circuit boards, the capacitors are the original and the amp is over thirty years old with absolutely no sign of capacitor ‘bulging’ or leakage. Most likely this is a rare exception, despite it having had much use. Have a careful look at any sample you buy and if there are signs of the top of the capacitor can bulging then replace immediately.


12-07-2011, 16:35
More information pointing to how and what to replace is great.........This is the reason I joined this forum as I have very little knowledge of the items. Thanks chaps for the responses so far.

I have been researching the vintage 'valve' amps as well....again so much to take in and to understand. There are many additional 'issues' with older valves equipment as well. Important and necessary upgrades for these 'golden oldies' are well documented on here.

I fully appreciate that a good example of any vintage gear would still out perform many of the modern stuff that you can buy new. The vintage/classic route is it for me then and lets hope that from listening to advice from you guys here and more reading up on the 'web' should prevent a potential money pit situation.:(

I have not even started thinking about what speakers to buy yet:scratch:

12-07-2011, 17:02
Nothing too demanding and with a minimum of 6 Ohm impedance is my recommendation, as the current limiting gets severely in the way with anything less..

These days, an early 606 isn't much more money on the used market than a tuned-up405-2, and to be honest, the 606 is a far more capable amp into modern speaker loads and has more power at it's disposal, audible at lower volumes too...

12-07-2011, 17:17
Another recommendation...:scratch:

I am looking at older speakers from the 60s/70s/80s so would a newer 606 be a suitable choice?

12-07-2011, 18:46
The 606 took the current-dumping circuit to a higher level. The mk2 606 had a toroidal transformer (not sure of this makes a difference) and 15000uF supply caps (the mk1 had 10000uF IIRC). A 606mk2 sounded "cold" like a mk1 well warmed up, and got slightly better again. Whether upgrading the mk1 supply caps to the later higher value would close the slight gap between the two I don't know, but all of the 606's will drive any reasonable speaker out there I think, where the 303 and 405 series will be a tad more particular, the 303 especially.

One final thing, the 405 series can have practically all the electronics with new improved parts, the only limitation being the small section case, which can get rather hot with some speakers. The current limiting in the 405's was there for thermal reasons as much as anything else I reckon. I'd happily have another though :)

Rare Bird
14-07-2011, 16:31
Quad '303' with a good 10K passive sounds great

14-07-2011, 17:26
NET Audio do lovely upgrades for the 303 & 405.

Rare Bird
14-07-2011, 18:22
The Net 303 Mk.III are my next purchase.

14-07-2011, 20:31
The Net 303 Mk.III are my next purchase.

Do you what do they do to them Andr'e ?, i still have my 33/303 both have been serviced and sound good, they need a bit of warming up to get the best from them though, my 405 mk11 hybrid thingy though sounds better

14-07-2011, 20:33
Are the 44/405 Quads good for 'feeding' a pair of Tannoy Monitor Golds?

14-07-2011, 20:48
Very interesting question, Pavalon.

15-07-2011, 06:51
A fettled 405-2 and vintage tannoys is a marriage made in heaven, as older Tannoy DC's present a "perfect" 11 Ohm loading from memory.

Don't forget Dada Electronics. Not expensive, loads of parts new and used, a great blog and also great service. I'm sure Net-Audio are fine as well, but I couldn't afford their 33 upgrades..

15-07-2011, 08:44
I've been toying with the idea of a 33/303 setup for my second system in the bedroom. I was wondering what a pair in good condition would be worth and roughly how much it would cost to update caps etc. to bring them up to date. :scratch:

16-07-2011, 21:03
Their was a guy (not gazemember) on ebay selling refurbished ones for circa £230 - £250 which to me sounds right, using desent quality components and someones time to do it. When looking at prices the 303's can fetch up to around £150 in original condition which is great for the quad purists but for sound quality and longevity completely refurbished is the way to go imo.


16-07-2011, 21:19
Their was a guy (not gazemember) on ebay selling refurbished ones for circa £230 - £250 which to me sounds right, using desent quality components and someones time to do it. When looking at prices the 303's can fetch up to around £150 in original condition which is great for the quad purists but for sound quality and longevity completely refurbished is the way to go imo.



16-07-2011, 21:31
No this guy http://www.briarsfield-hifi.co.uk/amplifier_rebuild.htm, i do a similar thing but don't like to advertise.

Rare Bird
17-07-2011, 04:40
I've been toying with the idea of a 33/303 setup for my second system in the bedroom. I was wondering what a pair in good condition would be worth and roughly how much it would cost to update caps etc. to bring them up to date. :scratch:

I love '303's infact i'm working on one now but the '33'! nay thanks

17-07-2011, 09:36
I am also considering a 33/303/ combo. I do like the 'iconc' design look of the 33/303 series. However I understand that they do need an upgrade for improved performance due to the lower grade components used in the original design.
A fully serviced pair of 33/303 from Quad or other specialist - will they out performed the later 45/405?

17-07-2011, 10:04
Dada do some excellent upgrade kits if you feel up to servicing yourself.

The 33 can be totally transformed IMO with the power supply revision and recapping elsewhere. I also found that replacing C400 (I think it was) on the output board with a 1uF cap (.68 fitted IIRC) takes the bass down to below 10Hz instead of brickwalling it at 30Hz and this opened up the sound no end on digital sources and allowed the sonics to "breathe," the results as big as the power supply upgrade IMO.

The thing with the 33, is that good original boards are available for not much money, so comparisons before and after are easy to do. I like my ton-up 33 and certainly am not looking for a 44. If the preamp is for a main system though, as said before, a LATE 44 will be fine...

The 303 is very much a triumph of its time, but the capacitor coupling and needed current limiting to 4A (to prevent the early ouput trannies from cooking themselves) can be a severe issue with modern 4 Ohm "Euro-Boxes." Give a fettled 303 a speaker it likes however, and it becomes an utterly charming little amp with a lovely midrange. I'm one of those who doesn't necessarily agree with souping the thing up to within an inch of its life with new boards, output transistors and front panel, but there are so many around still, that the choice is yours. The basic amp in good order is still a fine and charming, if small sounding thing.

15-08-2011, 09:11
Ok guys after a good few weeks break from the hi-fi trail. My search for a vintage amp from the QUAD camp starts again.

I have decided to go for a 34 or 44 with the 405-2 combo. Can someone here explain the main difference betwen the 34 (grey version) and the later 44 pre amp?

I know the 34 has 3 inputs and the 44 has 4. The facia design is slightly different but from a musical perspective which one is a better sounding amp?

15-08-2011, 09:24
The 34 has leaky-capacitor issues which affect the sonics and in worst case can damage the circuit board. I never liked the thing to be honest, much preferring the 44.

The 44 preamp went through something of a major revision later in life and the sonics benefitted much from the change I thought, especially in reproduction of jazz, rock and percussive music in general, somthing neither the stock 34 and 306 seemed very good at IMO (ugh!). The way you identify the later 44 is by the filter/tone cancel switch and (I think) the omission of the LED showing tone-defeat - HELP BARRY :)

The 405-2 needs several hours to fully sweeten up, a slightly steely sting being evident on the two I used extensively at home. The power hungry ATC's I used with the later one shortened this "warm-up" time to around an hour or so, by which time the case was luvverly and hot, but some of the later mods may eliminate this altogether.

P.S. What bothers me about the Net Audio boards is that they are mk3 for the 303. How much "better" are the mk3 ones over the mk1's, let alone the originals, which weren't cr@p by any standards? Andr'e, have a look at -


Good luck with your Quad hunt. Prices are rising, so tread carefully and factor in an amount for servicing.

15-08-2011, 09:34
I love '303's infact i'm working on one now but the '33'! nay thanks

THIS is the sodding page I was looking for regarding the 35Hz filter on the 33, which IMO constricts the bass and makes it "boppy" rather than "breathy."


Yep, C400, change from 0.068uF to 1uF (Wima's in my case). In conjunction with the dada power supply update (logically argued for on their site), the sound is transformed for the better IMO, making the 33 far more transparent to the signal it's fed with, certainly on the line stages.

15-08-2011, 12:44
The differences in performance between a serviced 34 and the 44 is likely to be negliable. I would therefore factor in the cost of servicing when considering the varying prices of these amps being offered for sale.

Thanks for the advice DSJR.

15-08-2011, 12:55
Have you ever compared the 34 and 44 when they were NEW? I did, on many occasions and over many individual samples. On music with any percussion, the differences in dynamic contrasts were sadly easy to hear. Adding a 306 to a 34 made it even worse, IMO.

A LATE 44/405-2, if these can be got in good order for under £500 (tricky I suspect), would be good value today. The only thing is, the Rega Brio R is too good to ignore for a decently designed MODERN solid-state amp.

P.S. I understand that the Current Dumping circuit was really only truly relevant in the 70's when output devices weren't supposedly as good/capable as they are these days. My Crown amps use an earlier derivative? of this idea I think, with an individually regulated Class AB stage driving equally regulated Class B output devices. The regulation on each transistor stage maintains reliability and circuit safety in a 19" rack and may just have a bearing on the sonics too.....