SpeakerTalk

[Lee in Montreal]

Between my mid-1990s NAD 1300 preamp and my 1979 Technics SU-9070 other preamp, there's a world of difference in sound, extension, presentation, etc. It may come from each unit's caracter, or from worn components. The Technics is very dry, precise but has an obvious lack of bass.

Now to the power amp. I also have another vintage unit here. 1979 Nikko Alpha II which is highly praised, but not as high end as, say, some of Sony's pro equipment. Anyway, witnessing the impact that a pre and a power amps have on speakers, I decided to bring my 405 Quad back into the action. Being old, it needs some TLC. As of now,I have taken it apart and deoxidised it. Al parts are now clean. I am awaiting for an update kit which basically consists of modern opamps, bigger power supply caps, small caps, RCA inputs and new speaker connections. For $99. I will start with this light upgrade, and if I lke what I hear, I may buy anther 405 and use them as mono amps. I won't have more power, but an almost unlimited source of current.

http://quad405.com/

(2) Power supply caps (12,000uf 80v)
(2) Burr Brown OPA134PA op amp
(4) .1uf 50v metal film caps for op amp (L48 104)
(2) 100uf 10v bi-polar cap for C2, Panasonic
(2) 100uf 50v cap for C5, Nichicon
(2) 47uf 100v cap for C10, Nichicon
(2) .000120uf cap for C8 (1F7 121K)
(4) 3.32kohm 1 w resistor for R7 and R8
(2) RCA inputs with hardware
(4) Speaker binding posts (2 Red 2 black)


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Current line up
2 sets basic Kef 104/2
2 sets bi-wire Kef 104/2
Plenty of KEF components for a few fun builds

[ColinR]

Read this by Keith Snook .

http://www.dc-daylight.ltd.uk/Valve-Audio-Interest/QUAD/QUAD-405-Modification/QUAD-405-Mods.html


At the last count I had 34 Quad items, all stock and serviced by Quad.

Regarding Quad 44 modifications you just need two 47uF Black Gates on the motherboard .
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This post or any other information supplied to this website or any other by myself is not available for any form of commercial purpose i.e. to hi-fi magazines or as sales and marketing material for sleezeBay or Audiodogging pimps and the like.

[Lee in Montreal]

[ColinR]

Quad PCBs use solder bath or "proper" flux cored Pb/Sn solder, try to use the same on small joints, as modern Ag/Sn muck is not miscible in most low ratios (0.5:1, 1:1, 1:1.5) and you're likely to get a "dry joint" .
_________________
This post or any other information supplied to this website or any other by myself is not available for any form of commercial purpose i.e. to hi-fi magazines or as sales and marketing material for sleezeBay or Audiodogging pimps and the like.

[TL 200]

"dry joint"
we wouldn't want that Colin, makes you cough you know!

[Lee in Montreal]

I just spent the afternoon working on the 405. It was not too difficult. All the components from the upgrade kit were easy to fit. The 405 sounds very nicely now, probably thanks to the 134 Opamps and a few current-liberating tricks. And it now has two RCA connectors in the back and a pair of decent speaker hook-ups too. A very well spent $99usd...

It seems the 405 and the 105/2 wee meant to be reunited. Sound is very pleasing. Now is the time to clean my ears as they probably are not optimally tuned...Listening to Modern Jazz Quartet, one ear doesn't pick the same as he other...

Next step is the 44.
_________________
Current line up
2 sets basic Kef 104/2
2 sets bi-wire Kef 104/2
Plenty of KEF components for a few fun builds

[Lee in Montreal]

I've been listening to my upgraded 405 for three days and can't believe how nice it sounds. It currently has a pair of 12,000µF caps (4,000µF more than stock in total) and some Bur Brown 134 opamps, plus many tweaks. I am currently looking for a dead 405 to build as a Franken 405. Brand new amp boards with BB627 opamps, 48,000µF caps and perhaps dual toroidal transformers. And perhaps, why not build two bridged mono 405 power amps in the same custom enclosure? Instead of being 13.5" wide, it could be a full 19" with full width heatsinks. Hmm...

If I purchased a good quality second hand amp, it will cost about $600-$700. For the same amount, I can build a brand new modern 405 and spend two days at home when it is -40˚c outside...
_________________
Current line up
2 sets basic Kef 104/2
2 sets bi-wire Kef 104/2
Plenty of KEF components for a few fun builds

[Lee in Montreal]

After being very satisfied with the update on my first 405, I decided to go a bit further. I purchased another 405 with one bad channel (distorted sound, meaning probably bad output transistors). I also purchased a few used amp boards from the same issue (issue 9) as well as two dozens of Motorola MJ15003G output transistors. The four boards will be updated with the same output transistors, new caps in a few places and opa604, as well as 48kµF dual PSU. Basically, the goal is to build two dual mono 405s in the same casing.

I also bought a Quad 606 with one channel blowing fuse. Again, the output transistors are suspected, but the amp boards will be updated too.

I am not a big fan of the Quad pre-amps, but do really enjoy their power amps for their simplicity. They are like toys, and there are many sources for upgrades.
_________________
Current line up
2 sets basic Kef 104/2
2 sets bi-wire Kef 104/2
Plenty of KEF components for a few fun builds

[proffski]

...continued...
_________________
I contend that for a nation to try to tax itself into prosperity is like a
man standing in a bucket and trying to lift himself up by the handle.
-Winston Churchill

[audiolabtower]

I built a 405 when they first came out after meeting Peter Walker at the first (Heathrow??) showing and being given the circuit and encouragement. I had plenty of test equipment at work at that time (the bridge components were matched to 0.1% by hand winding the inductor ), the only thing that was difficult to source was the output transistors, and I seem to remember buying them direct from Quad at £12 a set in 1976?

It is now on it's 4th set of power supply capacitors and had all the Ludwig/Snook mods apart from reversing the phase of the opamp.

The mods are definitely worthwhile, the modern opamp the most noticeable. It has never had low impedance speakers to drive, but even with all the mods is not quite as transparent, rock solid precise in image and as black a background as Audiolab power amps for example (I have tri-amped 105s now).

I've never had the chance of a long term listen to 606s, 707s etc to see if they are more competitive nowadays. I still think it was a brilliant design concept. Today it drives Kef Cresta 10s for a sampling synthesiser.

[iso]

I tried to open conversation about effects of DCR of inductors to electrical damping to long coil woofers. Proffski moved tread here, mut it seems that there is no interest on this interesting topic... I wonder why?

I noticed also audiolabtowers interest of Quads.I have wondered about quality of Quad 50 amps. They use output transforemers for proper load matching. Also inductor smoothing on HV is from valve amp period.

Circuity topology is quite much more complicated than Quad II:s. Output stage symmetry is propably very good due rransformer coupling and due similar otputdevices on both phase, I hav´t checked this but it must be so...

It would be nice if you can share your experience with this amplifier with us.

[DarrenHW]

Here is my hot off the bench take on 405 mono-blocking:



This has been a major improvement over the stock 405, stereo separation has improved significantly which along with the reduction in back ground noise has resulted in a far larger and immersive sound stage. There's a lot more detail coming through and the improvement in bass weight and control is like listening to a different amp.

I still have some work to do, I've not reworked the mains wiring as I'm still looking for a solution to incorporate an IEC socket and switch without cutting into the case, once this is done hopefully I can find a good place to secure the Velleman. I now have a spare brace of boards so will now focus on modifying these using Keith Snook's schematics.

The question is, are these considered mono blocks? I know the standard Quad 405 mono block bridges the two channels which I clearly haven't done, but surely these still constitute mono block, if not what are they?

[proffski]

Lovely 405 Quad type Monoblocks!
_________________
I contend that for a nation to try to tax itself into prosperity is like a
man standing in a bucket and trying to lift himself up by the handle.
-Winston Churchill

[DarrenHW]

Cheers Proff I wasn't sure how this would turn out and whether the "upgrade" would justify the expense, I'm happy to say IMHO it does. I know there's the question of expectation bias (and they do sound as I'd expected) but I would have been happy for the improvement to be minimal / pointless as it would have been 1 less 405 to buy, unfortunately it's back to eBay in search of another 2

[proffski]

Some of the best sounds I ever heard from a Hi-Fi was from 405 IIs and B&W DM70s both the Continental and UK versions.
Possibly the most accurate bass I have ever experienced, not the deepest but Hi-Fi!
The electrostatic panels were a treat for massed strings and vocal, female voices were incredibly portrayed as was grand piano etc. Sony also sold them with their logo. A perfect match!

Links: http://tinyurl.com/mahfen9 or https://goo.gl/avGSxH
_________________
I contend that for a nation to try to tax itself into prosperity is like a
man standing in a bucket and trying to lift himself up by the handle.
-Winston Churchill