One Thing Audio
One Thing Audio
OTEC, replacement ESL 57 treble panel
OTEC by One Thing
The OTEC, replacement ESL 57 treble panel
The OTEC, replacement ESL 57 treble panel
One Thing’s OTEC panel is a direct replacement for the treble panel employed in Quad’s ESL 57 between its introduction and final production runs in March 1984. To achieve better mid-to-high end detail retrieval, it employs an exceptionally thin front electrode (just 0.5 mm thick). This decreases significantly the impedance of the air within the perforations and results in a sweetness and clarity of treble not achievable in the original design. However, the ‘thin front electrode’ principle posed many design problems which took a whole year of patient research and experimentation to overcome. Special damping was devised to prevent the thin front electrode from ringing, and a hefty rear plate (not detrimental to performance as rear radiation requires curtailment anyway) ensures that the gaps remain uniform and the structure remains stable, even when flexed. Fibreglass (although expensive!) is incredibly strong, will not warp with time and can withstand high temperatures. The OTEC is now in its 6th year of production, with demand always exceeding our capacity to manufacture them!
Replacement type Quad ESL 57 Dimensions 19 x 65 cm Weight 2.6 Kg Electrode material Fibreglass Driven areas Copper-etched Rear electrode 2 mm Front electrode 0.5 mm Terminations Captive cable Colour codes blue, brown, red Polarising voltage 1.5kV +/- 12% Diaphragm material P.E.T.P Gauge 5 microns Coating Carbon paint Freq bandwidth 600 Hz—16 kHz Colour coding Copper/green comparison table
The OTEC ESL 57 treble panel has been developed to optimise performance in this critical area. Screw or soIder- tag terminations have been abandoned in favour of quality leads soldered directly to the electrodes, with due attention paid to the elimination of any shunt capacitance. Panel matching is within 0.5 dB. The panel is compatible, and therefore interchangeable, with any original Quad panel but the OTEC's tonal signature (especially high-end response) is such that changing in pairs, whilst not essential, is desirable in the interest of perfect channel matching.
The OTEC is guaranteed against failure arising out of manufacturing defects for a period of 12 months, but this does NOT include overload or abuse arising from excessive drive conditions without the use of a 'CLAMP' or voltage limiting board. Whilst refusal to use such a device is the owner's prerogative, it should be remembered that this limits the panel to low or moderate drive conditions only in low- powered systems. One Thing's newly-designed CLP4 clamp is strongly recommended for use in conjunction with this and any original Quad panel. It is a robust design which will not only hold peak voltages within safe limits but has no discernible effect on sound quality - this much we guarantee. The new board is simple-to-fit and supplied with easy-to-follow fitting instructions.
The OTEC is designed to give many years of trouble-free performance when used in the correct conditions, but if or when replacement becomes necessary, a brand new panel will be available with a 50% discount on the price prevailing at the time. This offer is permanent and ongoing to all owners of OTEC treble panels, and will be implemented simply by returning the 'old' panel to us (or the loudspeaker(s) if sent to us for servicing). This policy has been formulated to ensure that affordable servicing is available on our TOTAL REBUILD service indefinitely, irrespective of purchase date.
A frequently asked question addressed..
People occasionally ask us if we've produced a 'better' loudspeaker than Quad's original. This can be a tricky question to answer, as Quad's 'original' is so exceptional and unique that almost any answer will sound arrogant! What we have tried to address is the fundamental question, 'Would Peter Walker and his design team have changed anything in a loudspeaker designed in 1955 had they adopted the policy of most manufacturers and produced several 'upgrades'?' If the answer is unquestionably YES, there is logic in our attempts to produce, not necessarily a 'better' ESL 57, but one which incorporates some of the refinements and component upgrades which are possible in the year 2000 but not feasible in earlier decades. And the thinking governing those 'improvements' are well evident in the ESL 63, so there's not even much guesswork involved establishing which route Quad engineers might have taken had further improvements been a priority.
Ron Best
One Thing Audio
May 2005
Ron Best on the subject of "original" Quad panels
Why this happens – and whose vested interest it serves – is quite beyond me, but following another review in Hi-Fi World of our moded ESL 57s, the tired old debate about whose panels are closest in specification to Quad’s originals has been dutifully resurrected. There is most certainly a curious faction amongst lovers of the original ESL 57 who seem to regard themselves as custodians of original performance, and regard those who would change or digress from this as louts and heretics and unworthy keepers of the seal. We are berated for daring to change a performance and specification which is probably etched on a tablet of granite on mount Sinai and guarded by the spirit of the late Peter Walker. Nothing would induce them to pay a visit to One Thing Audio without a crucifix stitched into their clothing and garlic cloves rammed into their pockets!
So what have we done to earn this vilification? We tried to do sensible things and rescue a great design from the 1950s and make it give speakers in the 1990s a good run for their money. We think even our detractors would not argue with this. But some retro-obsessives still argue that the original performance - assuming the panels aren’t burnt to a cinder - is still preferable to (any) later-day upgrades. Having lived with a pair of 57s purchased in the early 60’s – and regularly serviced by yours truly for 3 decades (including dozens of other pairs for friends, family, and paying customers!) I find this preference baffling. ( If, indeed, it IS a genuine preference and not just an attempt to move on a pair of speakers at maximum profit without regard to their condition - and oh yes, “original panels and faultless performance, hardly used etc etc.” For some, a good selling-point it would appear). Even if these happen to meet an acceptable specification (which we have found to be the case in one pair out of every ten), they have absolutely no dynamics, and even with clamp boards fitted the nylon-coated treble diaphragm is likely to ignite at any moment due to an inevitable slackening of the tension which occurs over several decades. Treble will tail off rapidly after about 14kHz, and bass may seem acceptable but mainly due to poor treble which has shifted the energy spectrum. Some people may enjoy this (not unpleasant) sound – in fact it is quite “musical” – but you’re kidding yourself if you think this is what Peter Walker’s 1950s wonder should sound like!
And finally, the “original panel” debate. To throw any light on this confused subject, it is first of all necessary to decide what is an “original” Quad treble panel. The “moulded” panels – which I suppose assert the biggest claim to being original –
were used between the speaker’s launch date and the late 70s. This is the panel you will find as ‘standard fitment’ in 75% of the unserviced ESL 57s out there. It was a relatively reliable product because it was quite heavy and very stiff – but the plates were so thick that treble retrieval was adequate rather than excellent. Production problems (or costs) made it undesirable to continue with this product and the panel which replaced it had an indisputably better performance (as well as around 1db more output) and although this represented a far advance on the original panel – there was a sting in the tail. With its ‘rearwards’ curvature, direct sunlight or proximity to central heating radiators could cause the very thin plastic to warp, and the panel would go unstable. This makes this panel an unsuitable candidate for latter-day rebuilds, as the stresses imposed in the dismantling and rebuilding process make matters worse!
But the earlier panel poses fewer problems with respect to warping – but its thick electrodes are unfriendly to clarity and detail retrieval.This brings us to “modern” alternatives. Because they are made of perforated fibreglass warping ceases to be a problem. This is a huge advantage. But they do not sound like (or measure like, except very generally) original panels. Fibreglass is a very hard material, and its “tonal signature” is quite different from that produced by the relatively soft and well-damped plastics employed by Quad over the years. To maintain that one fibreglass panel is any more “original” than another is poppycock.
Yet it is only the “originality” standard-bearers who proclaim this as a virtue anyway.
Let us be quite clear about this: One Thing’s OTEC panel is NOT an original Quad panel. It does not strive to copy or replicate the performance of an original Quad panel. Nor (in our opinion) is it the slightest bit desirable that it should do so: those who carp about it on those grounds are not doing so to instruct or enlighten - or out of a desire to be truthful to the public - but are trying to point-score for purely commercial reasons. If a latter-day fibreglass panel doesn’t sound as good as a 20 year-old original Quad panel, it is because the builder hasn’t learnt his trade as thoroughly as the Quad engineers of yesteryear. But such a panel has considerably greater potential if built properly: certainly in terms of superior HF response, longevity, and power handling (especially the latter).And – sorry – using Quad’s original tensioning techniques does not make an original panel. “It was designed primarily to ease production and sample repeatability in the hands of relatively unskilled operators” [Peter Walker’s words, not mine!] But nevertheless – a wonderful piece of kit, if you can accommodate something the size of a billiard table.
Ron Best
One Thing Audio
September 2007