New Amps for Old

I bought my 405-2 a couple of years ago on eBay at a good price and had it re-furbished by 405man who sells refurbished 405s on eBay.

He replaced the power supply and a few other critical caps and he changed the controlling op-amp for a more modern one.

He promised me an amp "as transparent" as all but the very best modern amps.

I have certainly not been disappointed. The 405 and other Quad amps are, I guess, the foremost example of keeping good stuff in use, and even making improvements. Net Audio and other firm support these principles.

What does the membership think about keeping these veteran amps going in preference to spending on brand new kit?

I have heard it said that the modern amps can measure better than the best of the old, and the old designs don't handle so well the vestiges of RF noise that digital sources can squirt into them. I have not found the refurbished Quad wanting on either count.

Where do folk think the balance of advantage rests, with the new-for-old, or with the sparkling brand new?

 

If it's a quality amplifier which the 405 undoubtably is, I personally feel that all should be done to keep it going. I bought a brand shiny new Croft pre/power with that aim in mind. I would like it to see me through into retirement but maybe that is just being very silly and everso slightly naive.

 

The 405 is quite possibly a poor example to use here.

It is a giant amongst minnows in terms of what it represents in hifi history. It is incredibly good in theory (though some challenge the way Quad and in particular Walker chose to execute it) and is pretty much one of those rare timeless classics. It came at the beginning of an era when an awful lot of what was spewed out of the East is only fit for the skip now so I don't think you can assume everything from back then was good and worth keeping. The very best designs still stand up today which is why Quad current dumping is often emulated and New Class A isn't!

I run a Net Audio "mk 3" and in that respect chose to cheat. Old principle, modern components and the 20 odd years worth of hindsight that enabled a re-design to measure so much better than the original. Is it as enjoyable to listen to though? For me the answer is yes, for others that answer may well be no.

 

I'm usually against modifying kit these days as performance is often perfectly fine 'as is' but my recent experience with some older Quad kit did show some benefits, albeit more to absolute technical performance than any substantial sonic gains. Quad themselves refined the current dumping circuit over the years so some tweaking is okay IMO, especially as we are effectively applying the advantages of modern components to a 70s design.

Both versions of the 405 are perfectly fine without anything other than a service but you can make a few useful tweaks. The Mk1 does have fairly aggressive current limiting but that isn't an issue if your loudspeakers don't trigger the limiter.
The Mk2 is a lot better in this regard and will happily deliver 160w steady-state into 4 ohms - and 50w into any load. Now 50w into half an ohm won't do much but at least it doesn;t shut down or blow-up. Many amplifiers will.

The TL071 op amp on the input is old but perfectly good for the job it needs to do. The circuit requirements don't stress this part in any way.
Residual noise on the 405 isn't the lowest and substituting a modern op amp doesn't effect a cure - it does improve matters but only by a couple of dB.
Big reductions in noise require either a redesign of the input (to reduce Johnson noise) and/or a reduction in gain. I reduced the gain on my 405-2 and replaced the TL071 with a OPA134 to give a noise reduction of 10dB - well worth having.

So, new op amp, fresh caps, gain reduction and a general clean-up with perhaps some new in/out conectors are all that you require to have a 405 that will be more than a match for any modern SS domestic amplifier.

 

i have an old m.f B200 and still sounds super, o.k. few mods were made in 1990, but up to now when i want to play it it still cracks on wonderfully.

 

The circuit in the B200 is excellent - TdP at his best IMO.

It uses a high speed op amp at its heart and literally a handful of parts per channel. Simple and very good indeed.

I recently rebuilt a P170 power amplifier which uses the same Mosfet circuit but with a much larger dual mono PSU. Superb amplifier though truly poor build quality - much improved these days.

Must pick up a nice B200 for my collection.
P140 and Pre 3a are also great and effectively a B200 split into two cases.

 

Does the dual power supply mod for a 405 achieve much, Rob?

 

quote

rob, if you want to borrow the b200, you are welcome, it is mint ,

 

Not tried it Brian, but I doubt it.
The 405 PSU is certainly chunky enough for the job. The limited current is determined by a protection circuit designed to protect the output devices, not by any PSU limitation.

You will get some small technical advantage by splitting the transformer secondaries and fitting another rectifier and caps. Later dumpers do this but I doubt that anyone has actually taken the trouble to properly compare the two approaches on this range of amplifiers. If you've lots of free time and some spare cash, well it probably wont give you a worse amplifier
Would I bother? - Nah.

 

The main development in amps over the last 30 years or so has been the availability of fast, linear output transistors. The last really big innovation was probably the 405 itself with it's current dumping topology! (unless you include class D amps which have actually been around for donkeys years but only recently became capable of hifi performance). Other than that there has I suppose been a general learning curve as to which topologies and circuit techniques (which were around 40 years ago) tend to sound best/work together best or are most deserving of further refinement. Some of the most advanced circuit techniques, which are really flowering these days, came originally from the circuitry used in oscilloscopes... and much of it was first used in hifi by the Japanese in the '70s. OK many of those amps didn't deliver sonically but that was mainly due to such things as excessive feedback, over complex signal routing/switching/tone controls etc and puny power supplies in some cases.
The better power amps from the past can, when suitably serviced to give an even playing field, really impress. As has been mentioned in regard to sorted out 405's!
Remember how slated off the 405 was back in the day? It was total rubbish according to the comics of the day. You had to get a Naim NAP250 to be taken seriously back then.... and I know which one I would prefer, then and now :JPS:

 

Ah! Bedlington. I was born just down he road from Walkergate Sation and used to go to Whitley Bay on the electric train as a boy. God's own county. Best beaches in England. Pity bout the weather!

PS My 405 was refurbed north of the border! It sounds great.

 

It is indeed a nice part of the country!

 

Jez, Can i ask your view on swapping electrolytic capacitors.
I've gone from a position of, well if they are over 10 years old they all get replaced to a more selective approach. So I'll replace only under certain conditions, if the equipment is truly ancient, if there are signs of a problem either physically or in terms of measurement, or if the cap runs at high ripple (as with some valve kit in the PSU) or runs at high temperature.
If those conditions aren't met I tend to leave electrolytics alone.

What's your view?

Cheers,

 

That pretty much reflects my own views on the subject.
I often do change the whole lot though, both for customers peace of mind and because sometimes a full rebuild/refurbishment is the remit.

 

rob, regarding my musical fidelity b200, measurements on the upgrade made, for all it's worth specs are: power output:> 78 wpc, into 8 osms,
total harmonic distortion:< 0.25% "a"wid,
signal to noise ratio :> 78db, sounds awesome.

 

May I call attention to this question in my original post?

I have heard it said that . . . old designs don't handle so well the vestiges of RF noise that digital sources can squirt into them.

True?

 

Modern digital sources are, I think, better in the ultra-sonic and above muck they squirt out and it was really only the old prreamps with excessive yet simple filtering that seemed to react worse - I'm thinking early Naim and Quad preamps here. Modern CD players/DACs may not be a problem here and the Quad 33 I use for the headphone amp seems fine in its current tweaked form (the 44 with CD module onwards was fine I remember) and Naim improved their hf filtering, as well as making their own players pretty "clean" I think.

All my gear is ancient, decades old now, yet I'm getting as much musical enjoyment from it all as I ever did with "the latest model..." The 405-2 especially is a lovely old amp and the two I had only had the supply caps replaced because they needed to be after eleven years domestic use (physical leakage). The AVI mono amps (S2000 series) I replaced the last one with only sounded better with the ATC 20's I was using because of the extra headroom on offer - slightly more "ease" in the presentation I felt and, with the ATC's, the 405-2 ran extremely hot indeed (I was a bit of a headbanger back then and the 20's needed a ton of "rowing along" to make them come alive), yet the AVI's ran stone cold - a good sign for longevity I think if anyone takes a punt on a set fifteen years on.

Currently, my re-built Quad II's are out of the system over the holiday period and before I give my old bridged Crown D-60's another go, I've returned to a Quad 303, which the previous owner did some work on - lovely

 

A simple yes or no answer is not really possible on this one. Any well designed digital source should not be causing any HF nasties anyway. For over a decade now there have been European regulations regarding EMC for all equipment put on the market.
Therefore no item should either give out any interference nor should it be especially susceptible to it. In that regard it could be said that modern equipment is more likely to be ok in this respect.
However, competently designed equipment from the past should have no problems either.... There has always been plenty of HF and RF around and it has always been frowned upon for an amp to pick up radio moscow or the local taxi company

 

My first CD player (25 years ago, or near on) was a Philips CD 204 driving a Sugden A48 II which I only sold to a good home a couple of years ago.

At the time CD was new lots of folk were going on about the harshness. Some put this down to RF noise and added extra filtering to the outputs section of standard Philips chassis.

With my Sugden driving Tannoy 10" dual concentrics I heard none of this, and wondered what all the fuss was about.

Was it something like the start of the British motorways when many a family car blew up with the challenge?

But I am guessing that modern digital sources inject less RF noise so even with older amps there should be no problem.

What do those ATCs do Dave? My Quart floorstanders, nominally 4 ohm are driven by the 405-2 with only hint of heat.

 

i still have an old LUXMAN L85V, witch i love te sound of, my quad 33/303 although modified are super, great fun,