Quad 405 power amplifier
J. Gordon Holt & Sam Tellig, August, 1976
Model 405-2 power amplifier
"Current Dumping," a Quad invention, uses two output sections per channel—one a low-powered one optimized to reproduce sonic subtleties, the other a high-powered one whose services are called on by the other output section only when the need for brute force arises. We tested an early 405 some years ago but were unimpressed, as its sound was quite dull and, we felt, "slow." The 405-2 sounds like a different amplifier.
Like all European power amps, this one has substantially higher sensitivity than US and Japanese ones. (Sensitivity is the amount of input voltage needed for an amp to produce its full rated output. The US/Japanese standard is around 1 volt; the European standard is half that at 500 millivolts.) Higher sensitivity is not always an asset, because it can effectively raise a preamplifier's otherwise inaudible output noise up to the point of audibility. And since output noise originates after the preamp's volume control, it is unaffected by the setting of that control.
For instance, with loudspeakers of average efficiency, and every preamplifier I had on hand, the 405-2 produced a faint hiss background that was clearly audible in the absence of signal and during the pauses between CD selections. It was swamped by surface noise from even the best analog discs, but with more efficient loudspeakers, or ones having treble peaks, that hiss would have been raised several dB more, to the point of genuine annoyance.
There are two solutions to this: (1) use signal attenuators at the power amplifier inputs, or (2) use the 405-2 with a European preamp, such as the one Quad intended it to be used with, the Model 34. (Construction details for a passive volume control that would serve as an attenuator appeared in Vol.6 No.2.)
Also like most other European power amps, the Quad has no RCA input receptacles. Connections are made via a 4-pin DIN socket. An adaptor cable is thoughtfully provided, but the thought would have been appreciated more if the adaptor cable had not been defective on delivery. The RCA-plug ends were so sloppily wired that the shielding braids were shorting against the Hot terminal in both plugs. It was easily remedied, but an annoyance, nonetheless.
Sonically, the 405-2 presents a generally balanced spectrum but with a trace of lower-treble brightness, a subtle dryness, and a slight deficiency of low-end impact, probably attributable to the subsonic filtering. Imaging accuracy and stability are excellent, while depth reproduction was very good but not superb. Overall, the sound was very slightly dry.
In other words, as an isolated component, this is a very good amplifier but not a hands-down winner. It is handicapped at the outset by its price, the result of its origin in a country where production costs are comparable to ours, plus the markup which must be added when it is imported. And the fact is, the US still leads the world in power amplifiers that offer the maximum quality for the lowest price. The American-made Amber Series 70, for example costs the same as the Quad (granted, with no import duties or distributor markups), and is a better-sounding amplifier despite its lower rated power.
System Sound
After all the positive reviews of the Quad system—34 preamp, 405-2 power amp, ESL-63 speakers—that I have read (particularly in the British press, whose views are generally in accord with mine), I must confess to some disappointment now that I have lived with these components for a while...The system sounded smooth! But while there is no denying the musicality and listening ease of this system, the sound is simply not realistic, nor even a reasonable approximation of that. It is too smooth, too rich, too polite, and while certain instruments—fiddles, for example—are reproduced as well as I have ever heard them, most other instrumental sounds are more-or-less tainted with an almost cloying warmth that not even the Quad 34 preamp's Tilt control can cure. Gone is the bite of the trumpet, the thrum of the cellos, the blat of the trombone, the twang of the piano's upper-bass strings.
I am not speaking here of preferences in reproduced sound, and there are doubtless many people who will like this kind of reproduction. Indeed, it is exactly the kind of sound that many record collectors, given a choice, will prefer to the hyperdetailed renditions of an audiophile-type system. But to take a $3000 speaker system with the imaging and detail of the ESL-63s, and drown those attributes in a sea of haze strikes me somehow as a moral felony.
I love the richness and fullness of live orchestral sound, but I also love the rough edges that much live musicmaking produces, and it is those that I miss in this system. I still have the feeling that the '63s, mated with the "right" electronics, could deliver that level of fidelity without sacrificing their positive attributes (imaging, balance, detail). But I have not heard that sound from these speakers as yet, and until I do I can only say: Audition them for yourself. You may disagree with me.—J. Gordon Holt
This is something we don't see too often: an entirely new approach to power amplifier design. As Quad points out in its literature for the 405, class-A operation of transistors provides the lowest distortion, but drastically limits the amount of power an output transistor can deliver without overheating. (Most transistor amps use class-AB output operation, in which each of a pair of power transistors handles part of each signal cycle and shuts down during the other part. Imperfect synchronism between the two halves causes the familiar "crossover distortion," which accounts for most solid-state sound. In class-A operation, each output transistor draws current though the entirety of each signal cycle, eliminating the crossover transition but doubling the amount of time current is drawn, and thus tending to cause the transistor to heat up more.)
In "current dumping," a low-powered, low-distortion class-A amplifier is used to control the amount of current passing through a pair of heavy-duty "dumping" transistors, and it is the latter which provide the driving power (100Wpc) for the speakers.
The idea is ingenious, and while we cannot fault it on any theoretical basis, we must admit that the first amplifier embodying the principle has proved a bit of a disappointment. Our initial reaction on first hearing was that here was one solid-state amplifier that had neither hardness nor sizzle at the high end. It did not take us long, though, to observe that 405's high end errs in the opposite direction. It dulls the extreme highs—the ones that give air to the sound of strings and crispness to the sound of hard percussion. We were not surprised, however, to find that frequency response measurements failed to reveal the cause of the high-end dullness.
Other observations: Bass was somewhat sparse and a bit shy of impact, suggesting the possibility of some low-end (subsonic) filtering. Inner detail was fairly well-reproduced, depth was not very well-rendered, and the overall sound had a vaguely astringent quality to it—the antithesis of richness or warmth. For $410, we feel it is possible to do better than this. Perhaps faster "dumping" transistors might help.—J. Gordon Holt
Sam Tellig wrote about the 405-2 in April 1985 (Vol.8 No.4):
"You bought Quads again!"
Now my son really thought the old man was nuts. In my last installment, I told you how I sold my Quad ESL-63 speakers. A little later, I sold my Quad 34 preamplifier and 405-2 power amplifier. Unlike the speakers, however, the 34 preamp and 405-2 power amp were two pieces of equipment I wished I hadn't sold.
Once again, I find myself at odds with other audiophiles (footnote 1). The prevailing wisdom seems to be that the Quad ESL-63 speakers are super (indeed, they are very good) while the Quad electronics are, well, less than super. I'd put it the other way around.
It's strange. Even some Quad dealers are down on the electronics—perhaps because there are better choices for driving the ESL-63 speakers. In my opinion, the ESL-63 does a little better with tube gear (like the Quicksilver mono tube amps) or MOSFET amps (like the B&K ST- 140) than they do with Quad's own 405-2. What's overlooked, though, is how well the Quad 405-2 amplifier works with other speakers, the Spendor SP-l, for instance...
By way of preface, I'll first tell you of the joys of owning Quad electronics. First, they look nice. The 405-2 power amp is remarkably compact and good-looking. Second, it's beautifully built. Though not as lavishly put together as some all-out, price-no-object American power amps, parts quality is high, construction superb. Third, it is beautifully designed—a great deal of thought has gone into it.
Moreover, Quad electronics are known for their reliability. And they are well-behaved...The 405-2 power amp uses current limiting (another audiophile no-no), with the benefit that it is almost guaranteed not to destroy speakers. True, you can't blast away the way you can with other 100Wpc power amps, but the 405-2 was never intended for those who see their hi-fi systems as toys.
Quad doesn't keep changing models, so there's no phony obsolescence. They do make changes from time to time (witness their recent upgrade of the 34), but Quad owners are usually able to update their equipment easily and economically In fact, Quad has been known to supply some updates free, on request, for those who feel comfortable servicing their own units. But here's the payoff: you probably won't want to trade your 405-2 for a new model next year or the year after, because there probably won't be one.
The 405-2 power amp is very neutral, with just a slight touch of transistor hardness in the upper registers. It's more detailed than most MOSFET power amps, but not quite as sweet as MOSFETS or tubes. The 405-2, with its current limiting, is capable of dynamic bass, but doesn't have quite the kick of a Harman/Kardon hk870, a Threshold 5/150, or an Eagle 2. The 405-2 is probably a poor choice for driving difficult, low-impedance loads, such as Acoustats or Apogees.
Overall, though, the 405-2 is difficult to fault. I have yet to hear a perfect power amp, and the 405-2 is as good a combination of qualities as I've heard at the price....I can just hear Ross Walker groaning about this, but you might also try putting your 405-2 on Mod Squad TipToes or Sumiko Counterfeet. It's exciting what this can do, especially when combined with spiked speaker stands and a Target turntable shelf.
For me, the exciting thing about Quad components is that they offer a true alternative to typical hi-fi equipment. The equipment is beautifully built, handsomely designed, very reliable, and a triumph of ergonomics. Instead of questionable features and fashionable buzzwords, you get unusual features representing original thought and respect for the consumer. At $650 for the power amp, the price isn't exactly cheap, but the 405-2 represents good value. And you won't feel stupid tomorrow for having bought it today (footnote 2).—Sam Tellig
