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As Christian Steingruber has very well elucidated above there is a number of amplifiers that can drive the Quad ESL (original). Most of these amplifiers, admittedly, are of an "historical" nature, and indeed why not - the speaker is. It shows, however, that modern amplifier designers (in the main) have some way to go before achieving the prestige of some of there predecessors. Listed below are some modern amplifiers that fit the bill. In the end, the matching of your particular load to your particular amplifier must be done by you. This is the reason for so many people saying: "X sounds so much better than B" when in fact there are usually minimal differences, if any. We don't use that terminology here. We just say that it will drive the Quad ESL or it will not do such a good job. Which is "better" to your ears(?) - only you can tell.
The Velleman K4040 is a 100WRMS/Ch stereo amplifier manufactured as a kit (shock!! horror!!) by Velleman, Belgium. It is based on EL34 output valves (4 per channel) and operates in Push Pull mode. It drives the original Quads extremely well, even though, on the face of it, it seems far to "powerful" an amplifier for the task. If you are judicious with the volume control, the speaker when properly aligned will produce more than enough SPL to drive any sane listener from the room long before the speaker arcs internally. At 90dB the speaker is generally only "drawing" 12 to 15 Volts on the input terminals. All ESLs thrive on good current drive at output, and this amplifier can certainly provide that. Individual bias on each valve also means you don't really need matched octets (octaves?) of valves either. The heaters are AC, by the way. How does this amp sound? With Quads, very good indeed. I would say it is at least as good (and have said many times in the past) as amplifiers costing three times as much. Why not? You provide the labour and testing costs. You can replace parts (stock valves) with better components, and you don't have to make a profit. Hell, the mark up on some amps is 200% - but you didn't hear that from me - OK?
This is a 65WRMS / Ch mono amplifier from Velleman, Belgium. It uses KT88 valves (same as the new Quad II-40) at output and provides a 10dB lower noise floor than the K4040, predominantly due to the separation of th epower supplies. Again, more than enough current delivery for the original ESL, and drives it extremely well. The comments with respect to turning the gain up, as above, still apply. The bass performance is very good indeed. The amp uses DC heaters. What valves do I recommend - surprise(!) - JJ Electronics (not Tesla). They are superior to every other modern valve in this amplifier. The NOS Genalex MOV KT88 has the edge all around, but do you have the $4000 to re-tube the beast when it comes time ?
ME Power Amps
Modular Electronics Australia (Atherton, Qld.) make a whole range of power and pre-amplifiers that are very capable at driving all speaker loads I have encountered. The power amps drive the original ESL with no trouble at all. This is the nearest "sound" (if you indulge in this sort of language) that I have found in a transistor amplifier to a valve amplifier - if that makes the slightest sense. Suffice to say that the ME range has prodigious current delivery capacity into highly reactive loads and sounds very smooth (liquid) and accurate. The only caveat with the pre-amplifiers (perhaps) is that you must leave them ON permanently for the best sonic performance - not too difficult with SS gear, since it runs cool and consumes negligible power. The retail price is generally quite attractive too!
ME Pre Amps
There is a range of pre-amps, from the full featured ME 25 to the Line stage ME 24. If you have vinyl and need (therefore) a phono stage, then you need the ME 25. At about $AUD2000-00 it's a gratuity in the high end audio world. The ME 25 is likely the very best pre-amplifier in the world! That's very big talk, but I've heard 'em all (just about) and this pre-amp is so capable that it is not even worth raving on in the usual audiophile terms about it. Leave it ON always, and you wouldn't know you weren't listening to an Audio Research valve pre-amp in the mid-range, but in the bass, there is no competition - the ME beats 'em all, hands down. Beat the gadarene rush, and order yours now. Perfect for driving those long interconnects and keeping your power amp(s) where they belong - next to the speakers!
China is becoming a world force in amplifiers, among quite a few other things! The Ming-Da factory is perhaps one of the lesser known firms at the moment but they are turning out some excellent products, sonically speaking. About the only thing stopping the Chinese manufacturers taking over the amplifier world is the lack of third-party support in most markets. Although, I suppose, you have to give up something for the price. Certainly, neither sonics nor cosmetics have been sacrificed by Mind-Da and others!
These amplifiers all drive the Quad ESL (stacked or single) to deafening listening levels and retain stability while doing so.
I will be using this page in the future to post some down-loadable review documents of a few of the more interesting Ming Da amps starting with the S.E.T. MC-805A, a poweful (40WRMS) single ended triode job that (out of the box) is very musical indeed.
N.B. The document linked below has been copied by certain Internet retailers and used without written permission (copyright violation). These copies have also been edited by said retailers to reflect more kindly on their operations than the review originally indicates. This behaviour speaks for itself if you happen to be dealing with one of these retailers. This is no reflection on Ming-Da (Meixing) which remains a quality product.
Click Here for: Ming-Da MC805A Review