Quad 410

No, Quad have not capped off their recent release of the ESL 63 speaker with a new amplifier! The 410 is in fact the designation given to the 405 power amplifier when its channels are bridged together to give a mono amplifier of effectively 180 watts. In fact, it is even possible to bridge a pair of these 410 amplifiers to give a mono amplifier of some 350 watts. However, in this case the connections are a little more complex and 350 watts per channel is rather generous for most domestic installations.

The basci 405 has, in recent months, suffered some unfortunate criticism from those who seem intent on proving that it does not do well that which it was never designed to do in the first place, namely drvie very low impedance loads. This is rather like loading a small family car with four passengers and a caravan and suggesting the car does not accelerate well. The 405 was designed to provide 100 watts per channel into and eight ohm load, yet provide no audible contribution of its own. The amplifier wwas not optimised for four ohm loads and though it will drive them, it will do so with some reduction in performance (much like the car mentioned above). Circuitry is included to limit the amount of current the output transistors are required to handle, thus protecting them from currents in excess of their capacity, but also curtailing the amount of power available into the load. Whether or not you agree with the design philosphy is another matter, but the fact remains tha this is an essential part of the design and is clearly shown in the power output graphs provided with each amplifier. Removal of the protection does improve the sound quality into difficult loads, but makes the amplifier far more vulnerable to accidental damage, so you either over engineer the product so that it will cope with the extra current or risk a high incidence of failures. The 405 was designed to be economical to produce, ruling out the former, and no manufacturer who wants to stay in business can afford an unreliable product, which rules out the latter.
Some manufacturers of loudspeakers pay due regard to the amplifiers that may be required to drive them, whereas other free themselves of such constraints, but then few, if any, amplifiers drive them properly. There are arguments in favour of both approaches, suffice to say that this is a factor which should be bourne in mind when choosing amplifiers of speakers.
Some amplifiers, particularly those that have minimal protection, will operate in the area at which the signal begins to clip without audibly drawing attention to the fact. The 405 is not one of those and as clipping is reached the sound noticeably hardens up and becomes quite nasty if the level is advanced further. I personally see no justification whatsoever for driving an amplifier into clipping. If insufficient loudness is available then a more powerful amplifier or more efficient speakers are required. With high listening levels, low efficiency speakers and wide dynamic range recordings, it is all too easy to use up available headroom. of the 405, so it is useful to be able to increaes this headroom by bridging the the cahnnels to give around twice the rated power for the cost of a second 405.
The 410 is available to order, or the conversion can be effected to an existing 405. Quad will modify the amplifiers for you, or supply details on how it should be done. It is quite simple and anyone with a little experience at constructing electronic equipment will have no difficulty.
Such an exercise is only useful if the increase in power is not effected at the cost of sound quality, as is, regrettably, so oftne the case with such modifications. Quad assured me that apart from the 3dB increase in headroom and improved compatability with four ohm loads, there shoudl be no audible difference between the 405 and the 410. To see if this was the case, I merely substituted the 410s for my resident 405. The only difference in the system being the pre to power amplifier cable. However, I made up a new conencting cable using the same grade of wire and of the same lenght to eliminate this variable as far as possible. The rest of the system was the Linn/SME3 with a variety of cartridges, particularly the Dynavector Karat Ruby, Ortofon T30 transformer, PS111 phono pre-amplfier, Quad 44 and Monster Cable to ProAc Studio speakers. With mono amplifiers it is of course possible to eliminate most of the effects of the speaker cables by placing the power amplifiers  close to the speakers, but as this would have defeated the the object of this exercise by creating furhter variables it was not tried for the purposes of this report.
On audition, the essentially neutral balance of the 405 remains and in this sense, I have to agree that the amplifiers sounded the same. However, they omitted to mention that the extra power bestows a greater sense of ease and freedom from the hardening effects as clipping is approached and a clearly noted improvement in the dynamic capabilities, revealing the power and 'menace' of a large orchestra without compromise to delicate inner detail. Choral music, which gobbles up power, is more convincingly portrayed with greater transparency and separation of voices, showing an improvement in stereo separation. The 405 has always been very much to my perosnal taste. When bridged, the improvement is subtle but worthwhile and the extra headroom valuable.
I suspect that the procipal interest will be shown by Quad devotees who already possess the 405 and are looking for a bit more power, but the 410s are a viable alternative to a number fo more costly, high quality power amplifiers and a one of the least costly ways of obtaning an amplifier of this quality and power, should not be overlooked.

Graham Mayor
Practical Hi-Fi