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Quad current dumping amplifiers

J

johnfromnorwich

even my wife noticed the dif..
405 / 606 etc

I was considering one of these to partner with the ESL63s and keeping the valves for the Tannoys. I'm assuming Quad made these with their own speakers in mind. The 405 looks to be fairly cheap these days, 606 rather less so. Any experiences?
 
Both are fine with the electrostatics though if looking at a 405 you might as well go for the later 405/2. The electrolytics will need replacing by now so you'll need to add a minimum of £50 to the cost of the amp for a 405 - more for a 606.

Another option is the smaller 306 which uses near identical circuitry to the 606 running from a smaller PSU. These are rated at around 50w per side which is ample for a 57 and should be fine for 63. Cost is lower at around £150 but again you need to add around £50 for new caps.

Do not worry about current limiting or reports that output with these amps falls into low impedance loads - it does - but ESLs only present a low impedance load a very high frequencies were power demands naturally fall away.

All good, stable amps suited to pro and home use.
 
I had a 405 a long time ago. I found it smooth but a little boring. Very well made and worked fine with my TLs. They can be bought fairly cheaply right now as you say so I doubt you'd lose anything if you didn't like it. Oh, and they can be bridged too and they're reckoned to be very good like this.
 
The 405 is a safe choice for use with ESL63s and has held its value over the years.
I also had one a long time ago, I'd agree that is it nothing special but it is inoffensive and very well made - sort of like a 1970s Mercedes.

Another option to look into would be the "pro" current dumpers - 510, 520 & family. I've never heard one but they are pretty much the same circuit as the 306/606 and apparently have a more generous power supply (may make a difference with low impedance dynamic speakers, but perhaps not with Quad ESLs).
 
This current dumping prerequisite is somewhat discriminatory against the 303, which many seem to think of as Quad's nicest sounding solid state amp and certainly the most tweakable. Allegedly wonderful in stock form into ESL57, though don't forget that, like the 405 / 405-2, it phase inverts, so plug the speakers in black to red.

Tony.
 
Tony L said:
This current dumping prerequisite is somewhat discriminatory against the 303, which many seem to think of as Quad's nicest sounding solid state amp and certainly the most tweakable. Allegedly wonderful in stock form into ESL57, though don't forget that, like the 405 / 405-2, it phase inverts, so plug the speakers in black to red.

Tony.
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Tony - Was it a 303 we compared to the WAD/Icon/PL valve amps at yours? If so, I remember it being pretty much outclassed by all the others.

Incidentally, the 63s sound awesome with the WAD. I've just got a bit new owner neurosis about Pan Sonic melting the amp down. Also, it seems like a crime to leave the Tannoys mothballed.
 
I'd go for the 606, new caps and better caps in important positions...405 is a bit dull, ou can mod it till you drop, the 606 still drives circles around it...
 
johnfromnorwich said:
Tony - Was it a 303 we compared to the WAD/Icon/PL valve amps at yours? If so, I remember it being pretty much outclassed by all the others.
Click to expand...

Yes, but it was fresh back from a factory service (that was the first time I'd turned it on!) and was wired in the system out of absolute phase. I've not tried it again into the Tannoys, but it's sounding rather good into the Heresys now, certainly the nicest solid state amp I've had through them. I think it needed a little time for the new electrolytic caps to form or whatever as it's warmed up and opened out quite a lot, plus getting the absolute phase right is definitely noticeable - I like my music to blow not suck! I'm sure the Prologue 2 etc would still give it a kicking into the Tannoys, but it's hardly a fair comparison, the PL costs getting on for 1600 quid these days, a nice 303 can be found and serviced for under £200. It is allegedly at it's best into Quad ESL too, apparently sounding very similar indeed to Quad IIs, but with a little more bass grip. Regardless I'd be pretty amazed if you preferred any solid state amp to your WAD. I'm using the 303 as it costs very little to run (my back room system is on most of the day) and is pretty much bullet-proof. It's a great amp in this context.

Tony.
 
405s are often referred too as a bit boring and perhaps smooth.
I think that reflects the image of Quad the company as becoming rather conservative in the 80s and onwards but has nothing to do with amplifier sound.

A 405 if not driven beyond the spec sounds clean and faithful to the original input IMO.
Not boring but perhaps lacking the added spice that can be added by the technical failings of some other amplifiers.

To give an example, ESLs have a wildly varying impedance of around 30 ohms at LF falling to about 1 ohm at HF. So long as the amplifier doesn't current limit at normal listening levels - and most competent SS amps wont - the speaker produces the frequency response intended by the designer.
Substitute a valve amplifier and many, because of high output impedance will cause the ESL response to droop downwards at HF. So it sounds warmer and smoother - but this is caused by a technical failing within the amplifier design.

People will prefer what they prefer, but care needs to taken when interpreting results.
A few pounds spent on a pair of power resistors, or perhaps some long and very thin speaker cables will quite easily replicate such an effect.

One further point on the 405 and 306. The power supply and output stage on these designs is not the primary limiting factor with regard to low impedance drive. Disable the protection and these amplifiers will happily drive 4 ohm loads at high levels but they will become extremely hot in the process.
They are physically small amplifiers with limited heat sinking and totally enclosed cases.
Both contain small Class A amplifiers and therefore generate more heat at idle than a similarly rated Class B or AB amplifier.
The current limiting exists to prevent thermal runaway and make the amplifiers bomb-proof, but if you aren't pushing the amplifiers to those limits you don't have a problem.
 
Tony L said:
. It is allegedly at it's best into Quad ESL too, apparently sounding very similar indeed to Quad IIs, but with a little more bass grip.
Tony.
Click to expand...

It works well, a tiny bit softer at the top and fuller at the bottom than the dumpers on some music. Some key specs mimic those of the IIs so that isn't a complete surprise.
 
Thanks for all the input. I'll watch ebay for a while and see what comes up. Dunno what it is about these speakers, but suddenly I don't hate CD as much as I once did.
 
johnfromnorwich said:
... Dunno what it is about these speakers, but suddenly I don't hate CD as much as I once did.
Click to expand...

Weird, I have the same with my ESL57s - CD sounds better than I remember via my SFs, vinyl is still better but less so subjectively to me.

Richard
 
Odd speakers, they reveal superb recording and production yet also flatter stuff that is less good.
Even sound fine on the line out from an iPod!
 
The 405 sounds very good with one of the kits bolted on ( I used the Dutch one - Pilgham Audio). Absolute bargain (amp, not the kit, which is a bit pricey). But the Mk2 is definitely the one to go for, as the protection circuitry is incorporated into the cards, which makes things easier when doing the mods.
 
Having had several 405s of both versions IMHO the biggest difference is down to the age / condition of a particular unit (ie the state of its components and whether serviced) rather than 405-2 being better than 405 as such.

They have a laid back presentation, a little like being at the rear of an auditorium with the performers up on stage, whereas some amplifiers are more "front row". This is an issue of taste rather than performance, I kept a pair of 405s after I moved on to Exposures because there are times when I still like that style.

You can pick up a beaten up 405 for £75 or a decent model of either version for £150+, so there's nothing to lose.

Pete
 
I ran Quad 405s for years, they are great. Used one on ESL 63s for a year or so. I now run 57s, great too, but now I have valves which I prefer. I recently sold a 405-2 and a 405-1 for £250 the pair, the Mk1 did need a service.

They are bulletproof as stated, and loads of mods are available.
 
stevec67 said:
I ran Quad 405s for years, they are great. Used one on ESL 63s for a year or so. I now run 57s, great too, but now I have valves which I prefer. I recently sold a 405-2 and a 405-1 for £250 the pair, the Mk1 did need a service.

They are bulletproof as stated, and loads of mods are available.
Click to expand...

Steve - Two questions: I'm also running valves at present but regularly have the system running for 6-8 hours at a stretch, so having a decent SS alternative seemed like a good plan. A bit more bass grip would be nice too. How much of an improvement was the valve amp over a 405? Night and day or just the usual trade off of bass vs. mids? Second, Will Quad service a 405 themselves or am I looking at third party?
 
If you must have Quad solid state amps to go with ESLs, I think that a freshly serviced 303 will partner 57s best and a serviced 606 MkII will go best with 63s.

Naim CB or Olive amps produce lovely music with Quad ESLs (rather better than Quad amps, from my experience).

Graham
 
graham55 said:
If you must have Quad solid state amps to go with ESLs, I think that a freshly serviced 303 will partner 57s best and a serviced 606 MkII will go best with 63s.

Naim CB or Olive amps produce lovely music with Quad ESLs (rather better than Quad amps, from my experience).

Graham
Click to expand...

Out of my price range though!
 
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