Gang of Five
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Gang of Five
Madness strikes at all hours of the day and night, so I can’t tell you exactly when it occurred to me to assemble a collection of treble panels from all the major Quad panel refurbishers and rebuilders, but I suspect it was just a couple of months ago - it seems longer. The panels examined in this review are a mixture of new replacement panels for the original Quad treble panel and rebuilt original Quad treble panels. The new replacement brigade consists of Quad, Germany and OTEC, England. The rebuilt original panels are (in strict alphabetical order by surname) from: Stewart Penketh (Canada); Wayne Picquet (U.S.A.) and Sheldon Stokes (U.S.A.). All five panels were acquired directly from the manufacturer or rebuilders with the exception of the Stokes panel, which was acquired from an intermediary, but is definitely identifiable as a Stokes rebuild. The intermediary, for reasons of his own, wishes to remain anonymous, but is curious to see how the panel stacks up against the others. My view is that we could hardly have a meaningful comparison of rebuilds without the work of the man who started this rebuilding madness a few years ago, so the Stokes panel was seen as an essential inclusion. Other rebuilders I’m sure would be curious on this point also. Let the games commence!
OTEC, One Thing Audio, Coventry, England
The OTEC panel is a newly manufactured panel, not a rebuild. The panel is of standard size (647mm x 190mm x 18mm) (L x W x T) overall. The stators are made from what appears to be glass fibre reinforced circuit board material which is appropriately perforated in exactly the same staggered pattern as the original Quad panel with ~3mm diameter holes. The conductive areas on the inner surface of the perforations appear to be plated copper such as one would find on a printed circuit board. It is assumed that this is precisely how the stators are made - using an etching process of some kind. The stator material is ~1mm thick, which is thinner than standard Quad panel stators (~2mm thick PVC). The edges of all the perforations have not been cleanly de-burred but left with a rough circumference after what is assumed to have been a drilling (rather than a punching) process. The stators exhibit considerably more mechanical flexure than the original Quad treble panel stator. This is mostly a consequence of the thinner material in use. The wooden frame used to stretch the dust covers is of thicker material (~8mm) than the original Quad panel (~7mm) and of a rather better quality wood than the original. This mechanical artifice produces an overall panel thickness identical, as mentioned above, to the original Quad panel. The panel is penetrated through its full thickness at four points as per the original Quad treble panel to allow the passage of 2.5-3mm tensioning bolts. The bolts and nuts used are nylon (presumably to reduce leakage on the panel). The washers used appear to be identical to the felt washers used on the original Quad panels (and indeed, may be recycled Quad washers for all I know). The panel is physically fastened using M3 (3mm) crosshead steel bolts and nuts. The bolts have been carefully selected for length so that they do not interfere with the rear dust cover. The nut tightens exactly flush with the end of the bolt at the rear preventing possible tearing of the rear dust cover by protruding metal thread. The nuts have been sealed in place with a thin lacquer that should prevent any loosening of the nuts over time due to the normal operational vibrations. The perimeter of the panel appears to be glued in place so that the problem of bolt length does not intrude upon assembly of the panel around the perimeter. The dust covers are made from what appears to be 6-micron PET film. I am advised by the manufacturer that the diaphragm is 6-micron tensilized PET film, and that the diaphragm coating is a proprietary carbon-based material with a surface resistance of 10^9 ohms per square. The manufacturer also advise that a higher tension is used than that adopted originally by Quad. The panel is well sealed around the perimeter using a good quality clear, conformable tape. I suspect a certain 3M product, but I have no evidence that it is. Connections are of standard configuration and colour coding as per an original Quad treble panel, so the non-professional installer could probably manage to get one connected correctly first time around.
German Quad, Musikweidergabe, Koblenz, Germany
The Quad, Germany panel is a newly manufactured panel, not a rebuild. The panel is of standard size (645mm x 192mm x 17mm) (L x W x T) overall. The minor variations in size are not significant as the panel can be mounted easily in an original Quad ESL with no problem. The slight decrease in the thickness can be taken up with felt mounting pads. The stators are (as with the OTEC) made from what appears to be glass fibre reinforced circuit board material which is appropriately perforated in exactly the same staggered pattern as the original Quad panel with ~3mm diameter holes. The conductive areas on the inner surface of the perforations appear to be plated copper (as per the OTEC) such as one would find on a printed circuit board. It is assumed that this stator is made using a circuit board etching process of some kind. The stator material is ~1mm thick and exhibits considerably more flexure than an original Quad stator. This extra flexure is again, most likely due to the thinner material in use. The edges of all the perforations have been cleanly de-burred and the finished circumference is very clean. So clean, in fact that it is impossible to tell whether the stator is drilled or punched during manufacture. The wooden frame used to stretch the dust covers is of a similar thickness to the original Quad panel (~7mm) and of a very similar quality wood than the original (apparently a light pine). This produces an overall panel thickness approximately 1.5 mm less than the original Quad panel, but this is hardly a critical point when fitting the panel into a speaker. The panel is penetrated through its full thickness at four points as in the original Quad treble panel to allow the passage of 2.5-3mm tensioning bolts. The bolts and nuts used are nylon (to reduce leakage on the panel). The washers used are made of a white, felt-like material which is a little thinner than that used on the original Quad panels. The panel is physically fastened (stator to stator) it is assumed by gluing along the central strips and the perimeter, as only four mechanical fasteners other than the dust cover tensioning bolts can be found. These fasteners penetrate the panel for its full thickness on the central strips approximately 90mm above and below the standard dust cover tensioning bolts. These four extra bolts and nuts (two top, two bottom) are of nylon. The stators are insulated heavily at the perimeter with tape before the dust covers are fixed on to the stators. The diaphragm material is original 6-micron tensilized PET since Quad Germany has the original jig and materials, purchased some years ago directly from Quad. It is assumed that tension in the diaphragm is identical to the original Quad panel since this panel is assembled on the original jig. The dust cover material appears to be 6-micron PET film and is probably also original Quad film. The panel is well sealed around the perimeter using a good quality clear tape, but this is of lesser thickness than used on the OTEC panel. Less insulation may be allowed at this point because the edges of the stators are already well insulated before the dust cover is added. The manufacturer advised at the time this panel was supplied that the coating material was a form of soluble nylon (probably Elvamide). Hence we would expect a surface resistance of 10^12 ohms per square or that vicinity. Connections are of non-standard configuration compared to an original Quad treble panel, so the non-professional installer could go quite potty trying to connect this panel in a speaker without care or explicit instructions from the manufacturer. The eight (8!!) connection wires exit the rear of the panel through some rather rudely drilled holes (splinters abound), and the connection order is (from the rear): blue-rear; blue-front; red-ht; brown-rear; brown-front; red-ht; blue-rear; blue-front; where the “front” and “rear” refer to front and rear stators. Clearly the appropriate ”fronts” and “rears” need to be matched up, twisted together and then connected to the audio transformer. Likewise the HT pair should be connected to the 1.5kV terminal on the EHT block. There is, at least, a good length of wire to work with! The connection wires have adequate flexibility, insulation and gauge for the job.
Stewart Penketh, Montreal, Canada
The panel is a rebuild of an original Quad treble panel. The panel is of standard length and width (647mm x 190mm) but slightly thicker than standard at 20mm. The latter dimension is due to the use of steel bolts to fix the perimeter of the stators to each other. It may be slightly more difficult to assemble the panel into a original Quad frame for this reason, but I doubt any major problem would be experienced. Stators require scant description being of 2mm PVC, (original Quad), and the perforations are of course original. The stators have not been mechanically refurbished, as one can observe a little plastic swarf around one or two perforations as one finds in factory originals. The stators have been cosmetically dabbed (retouched) hear and there with a matching gray paint. The overall appearance is that of a new stator. The stators are mechanically fixed throughout with 3mm crosshead steel bolts and nuts. The threads of the bolts do protrude (~1.5mm) from the nuts on the rear stator. This does not present a major hazard to the rear dust cover given normal handling. The dust cover is of a thinner than “normal” material and the builder advises that it is Saran film, not PET film. The dust cover is penetrated by the usual 4 tensioning bolts. The bolts, nuts and washers used on this example appear to be all original Quad fittings. The dust cover frame is also an original with glue stains to prove it! The edges of the dust cover frame are well sealed with a gray-coloured, heavy, fabric reinforced insulating tape. The builder advises that the diaphragm of the unit is 3-micron Mylar, but the has supplied no details on the tension or coating used. Connections appear to be stock, standard original Quad wire. The EHT bolts to the front stator have an additional connection utilizing small (2mm wide) copper strips. The overall appearance is of a high quality rebuild. Stop Press: Some problems were experienced with the first panel supplied and to his great credit Stewart replaced the panel with another within a very short time. This is the kind of backup that every customer would like to think is there from every rebuilder. I believe that in every case represented here that this kind of service is available, but in Stewart’s case, I know so. The second panel was mechanically slightly different being assembled with shorter bolts and of the same dimensions as an original panel. I believe this to be of significance to people who are buying a part and fitting their own panels to the speaker.
Wayne Picquet, Florida, U.S.A.
The panel is a rebuild of an original Quad treble panel. The panel is of standard dimensions in all respects. Stators are 2mm PVC (original Quad) and perforations original. The stators appear to have been mechanically refurbished as no visible burrs or swarf was detected during a very close inspection with a 5X lens. Close inspection with this magnification indicates that the stators have probably been lightly sanded and re-sprayed in the original Quad gray. This gives an “as new” appearance as one might expect. The stators are fastened at the edges with tape or glue. No mechanical fastener is apparent, and this is consistent with the panel thickness. The central strips are held together with recessed, flat head bolts that appear to be stainless steel. The bolt thread does not protrude to the rear of the nut; hence there is little danger of the rear dust cover being damaged by a bolt. The dust covers appear to be 6-micron tensilized PET film. The dust cover tensioning nuts and bolts are of nylon and the washers appear to be original Quad felt washers. The dust cover frame has been completely cleaned and sanded back showing no signs of its origin, but for one or two deep stain spots (2mm dia.) that indicate it is a refurbished Quad frame. The builder advises that the diaphragm is 6-micron tensilized PET film and it is coated with soluble nylon. The electrical connections are stock, standard original Quad wire that has been nicely cleaned up.The overall appearance is of a factory new panel.
Sheldon Stokes, New Mexico, U.S.A.
The panel is a rebuild of an original Quad treble panel. The panel is of standard length and width (647mm x 190mm) but of greater than standard thickness, being ~24mm thick compared to a stock ~18mm in an original Quad panel. An inexperienced installer might be pressed to get this panel into an original Quad frame. There is considerable movement in the dust cover frame at the top of the panel as it is held well away from the stators by the bolts that fasten the stators. The stators have the appearance of an original stator where the tape has been stripped off and the stator cleaned up afterward. There has been no cosmetic retouching of the stator. The stators are fastened to each other with standard length M3 crosshead steel bolts and nuts. The bolt threads protrude from the nuts at the rear of the panel. In this example, the rear dust cover has been “bruised” at several points by these protruding threads. Careful handling is clearly needed, and the Customs Inspector didn’t “handle with care” to that degree. The dust cover frames show all the usual glue stains that one expects to see on a factory frame that has been cleaned up but otherwise unmodified. The dust covers appear to be of a 6-micron material, probably PET film. The dust cover is well sealed around the perimeter with a high quality, clear tape. The dust cover on this example was slightly loose and required minor re-tensioning with a heat gun. The original Quad dust cover tensioning bolts have been replaced with new steel bolts and the original Quad felt washers re-used. No information is available from the builder regarding diaphragm thickness or coating, but this builder was known to use a metal oxide suspended in water-soluble polyester glue at one time.
Electrical Measurements (for those who need them)
All panels underwent the same basic electrical measurements that tell us nothing much (except in gross) about how a panel will sound in operation. Nevertheless, it is a worthwhile exercise in that it would reveal any major anomalies that may be present in a given example. A grossly anomalous measurement would indicate a manufacturing fault, and it would not then be fair to listen to that panel without giving the manufacturer/builder a chance to replace it with one which is up to their specification (in the case of new panels) or the Quad specification (in the case of rebuilds). Other than this precautionary tale, I am not a great believer in electrical measurements telling us anything about a panel’s sonic performance, and indeed this is true of original factory panels as well. After listening tests were complete, panels with unknown coatings were disassembled and the surface resistance checked with a high quality meter in a static free environment. They appear below in alphabetical order by company name or surname.
German Quad, Musikweidergabe, Koblenz, Germany
The frequency response of the panel was essentially a 1:1 mapping of an original panel from 500Hz to 5kHz. However, the output of the panel was 2 to 2.5 dB less than that of an original Quad panel in this range. Between 5kHz and 6.5kHz there was a further drop in output from this panel compared to an original Quad panel of 8dB. The response curve was also slightly frequency shifted in this region. This panel came nearest in output to an original panel between 6.5kHz and 7.5kHz. From 8kHz to 20kHz this panel exhibited 76dB +/- 4dB output. This is quite dissimilar to a Quad original that has a slightly rising characteristic above 8 kHz with a distinct peak in the response around 15 kHz, declining thereafter. These measurements suggest a panel with a lower overall output than an original Quad panel, but also some recessed mid and high frequency character. Electrical measurements aren’t everything though.
OTEC, One Thing Audio, Coventry, England
The manufacturer did warn us that this panel was distinctly different to an original Quad panel and is designed to work with the OTEC bass panel. We tend to concur with this from an electrical point of view, given the following observations. The capacitance of the panel is slightly different to an original panel, and may need to be run with minor crossover network modifications in the original Quad. The frequency response from 500Hz to 5kHz is essentially a 1:1 mapping of the original Quad panel with a slight “dip” at 7.5 kHz. However, above 8kHz things do alter. The OTEC panel has a distinct peak in the 11kHz to 12kHz area exhibiting ~2 dB more output than an original Quad treble panel. Above 12 kHz and up to 20 kHz the panel starts to rapidly drop in output and at 20kHz has dropped ~14dB with respect to an original Quad panel. This suggests a panel that will lack ‘sparkle’ in comparison to an original (say) and add an odd emphasis to the high range of some acoustic instruments. Again, electrical measurements aren’t everything.
Stewart Penketh, Montreal, Canada
The panel maps the performance of an original Quad panel across nearly the full spectrum tested (500Hz to 20kHz). However, the output of this panel is, in places about 1dB below that of an original Quad panel. The frequency response, apart from the lower amplitudes tracks the original very closely with a slight lift at the top end around 15kHz to 20kHz. The panel has considerable extension out to 23~24kHz and this is probably due to the 3-micron diaphragm film. The panel is more efficient at high frequencies than low frequencies, in other words. This suggests a panel that might seem a bit bright perhaps, but listening tests do not bear this out, as we will see later. The panel was a bit “spitty” when first mounted in the speaker system but settled after 24 hours or so to be quite silent, or at least, no more crackly than original panels. This panel did measure lower in capacitance than an original, but whether this will have a sonic effect remains to be seen in the listening tests.
Wayne Picquet, Florida, U.S.A.
This panel response was a 1:1 mapping of the original panel response with a very slight lift in the upper frequencies, +1dB at 12 kHz ~ 18kHz compared to the original. The panel response is otherwise an unremarkable mapping of the original panel response with a little more output at and over 20kHz. The capacitance of the panel is very similar to the original indicating the use of the original coating, which this rebuilder is known to employ. The sensitivity of the panel is very much on par with the original at around 87dB.
Sheldon Stokes, New Mexico, U.S.A.
No frequency response surprises here. The panel is a virtually identical frequency response mapping of the original. A few minor (0.5dB) variations from the original can be dismissed as systemic errors either in the original measuring environment or in my measuring environment. The sensitivity is excellent and on a par with the original panel (~86-87dB). The panel exhibited a low level “fizz” when installed, as the diaphragm charged. This very low level noise (audible only with an ear on the grille) persisted for about an hour and was possibly indicative of a very high resistance coating on the diaphragm.
Two “systems” were used for listening tests. The first was my everyday listening setup with Quad II/40 mono amps and ME25 pre-amp (SS) in an acoustically treated room. The equipment under test was not varied at any time, nor any alterations made to the room; so, to all intents and purposes the panel under test was the only variable (not counting room temperature which varies a couple of degrees from day to day). The second “system” was a pair of single Quads with one pair having the panel under test installed for listening tests. The same amplifiers, wire, sources, room were used for the listening tests with the single pair as for the stacked Quads I normally use. This was thought prudent, since it is well known that the sound of these systems changes quite a bit as the load is changed on the amplifier, plus the fact that the large speaker array simply puts more energy into the listening space. Listeners were “pressed” into service over a reasonably wide age range (mid-20s through mid-60s) and so it is to be expected that some listeners heard things that others did not because of this (age) factor alone. I refrain from any comment while listening tests are conducted (single blind, since I know which panel is which, but they do not), and simply ask for comments, musical and technical to be written down. I do not like to pre-empt any response from listeners by having pre-arranged questionnaires that might have some bias to them. So, for the stacked Quads all the listeners knew was that there might have been a “new panel” in one of the stacks - maybe.
The actual case was that an original Quad panel of good specification was in all positions in the stacks but for the lower panel in the left hand stack for all listening tests and the panel being “tested” was the lower treble panel in the left hand stack. The original Quad panels were matched within 1 dB of each other - an exercise in itself, to arrange ! A complete other saga which I may write into my memoirs one day J entitled “Lord of the Panels - The Return of the Sorcerer’s Apprentice”, with apologies to Paul Dukas and JRR.
German Quad Panel
The German Quad Panel that was listened to is about 18 months old and the manufacture may have changed since then. This panel supposedly has a nylon coating, but I wonder, given the sounds it made. All listeners generally commented on the panel as being “soft” sounding. The fact that the panel was easily picked form the others tells us something about both sound quality and efficiency in this case. The aural indications align pretty well with the electrical measurements as well, and the panel lacks sparkle in comparison to the originals and indeed in comparison to others in this survey. The panel sounded comparable to an original in the overall quality of its mid-range reproduction but percussive instrumentation was reproduced in a duller fashion, or “soft sounding” as noted above. Extensive listening to the panel convinced me that it is in fact lower in output than a standard Quad panel and not as “exciting” to listen to. This rather odd remark is something I normally couldn’t say about a Quad panel and the impression here is of a panel that is not actually coping with transient material as well as the others. Again, I strongly suspect that this is tied to the tonal qualities of the panel and has nothing at all to do with actual transient response (mechanical/electrical movement) of the diaphragm. Some comments from listeners, in common:
- “The balance is off a bit.” (L-R balance, but altering the controls didn’t soothe - GJJ)
- “Percussion sounds ‘close’ but muffled and that makes no sense if you’re physically close to the instrument” (or the microphone is - GJJ)
- “I can hear that the system does not sound as ‘fast’ as it normally does, but maybe that’s just me.”
- “… system does not seem as ‘open’ as usual, as if one of the panels was connected out of phase…” ( we checked, twice - it wasn’t - phew - GJJ)
These are fairly critical things to say and in isolation I suspect that a pair of these panels would sound quite good. The panel is of new manufacture and employs a thin circuit board material in the stators that I am beginning to form certain hypotheses about - more on this later.
In the single Quad setup the effects noticed above were more frequently commented on but the tenor of those comments was in line with what is shown above. It would appear that you still cannot expect to put this panel in a system with an original panel and not hear the difference.
OTEC, One Thing Audio, Coventry, England
To use Ron Best’s words: “It’ll sound a bit like a fish out of water with an original bass panel.” This was said in reference to the panel we had for listening in these tests although Ron did not originally supply it for the purpose. I was curious to hear one, and One Thing Audio kindly offered. This is a new panel with thin stators (yes, more on that little factor later). Listener’s comments on the panel in comparison to the originals in the stacked array were very similar to those quoted above for the German panel, so it is probably not worth repeating them. The panel gave a “soft” overall performance, although the mid-range is lacking nothing in actual detail when you sit and listen closely. The parts of the music are all there. There is no loss of absolute pitch or rhythm, but there is a loss of excitement in the music. There is a loss of some of that immediacy that an original Quad panel has in abundance without being “in your face” about it. It is likely that this panel has to be used with some kind of crossover modification and with its corresponding One Thing Audio bass panel partner to give the impressive performances described elsewhere in the audio press. This is fair enough comment in itself but I feel it will not satisfy the original Quad owner who requires the original Quad ESL sound. Listening to a single pair of Quads with this panel installed in one of the pair simply further emphasised the differences between this and the original panels. A definite imbalance and lack of ‘excitement’ and even a partial loss of the fabulous openness of the original speaker was noticed. Once again, I could only ascribe this series of impressions to tonal differences because the panel gave no obvious mechanical clues to any lack of transient response.
Stewart Penketh, Montreal, Canada
The listening tests had to be redone for the second panel that Stewart supplied. There was an unfortunate mechanical failure with the first. This sort of thing has happened to every Quad builder, including the factory. What is important is that Stewart replaced the panel in double quick time and would do so for any of his customers. What about the sound of this panel? Comments as follows:
- “I can’t really say which panel is which…you’re not having us on, are you…?”
- “Are we the placebo group this time, Gary?”
- “OK, I may be getting on a bit, but I can’t hear any difference at all in the system.”
- “…er, ummm, might be a bit more open than I can remember, but the whole thing sounds so bloody good, I really couldn’t say.”
- “…nothing, really. I just think it sounds like musical instruments playing music like it usually does.”
This says something for the extent of the usefulness of electrical measurement. This panel did have significant upper frequency response differences to an original Quad (nothing below 15kHz though) and yet listeners detected no difference in the stacked set up whatsoever. This is after quite long sessions of an hour or more. If I sit and listen to the system with knowledge that it is in there, then perhaps, I can imagine that I can hear the slight lack of output at some frequencies (I know from measurement are present) that is there, but it really is a bias and then only if I listen to a passage I am very familiar with and paying strict “review mode” attention to everything. Otherwise, it’s “Shit, Can I really hear that (?) - Play it again (Samwise).”
In a single set of speakers I thought there might just be the odd listener who would pick the sound of this panel; but no. So, I can be reasonably confident in saying that you can put a Penketh panel in your original Quad and not hear the difference given that you allow it to charge properly. Stewart’s panel charges quite rapidly by the way, but I like to allow 24 hours for things to settle in any case, wherever the panel comes from.
In short, expect all the openness, sparkle, transient surprise and tonal accuracy that you expect from the original from one of Stewart’s panels. Ignore any comments I’ve made above regarding electrical differences, as they are only that, and they appear to have no significant bearing on the sound.
Wayne Picquet, Florida, U.S.A.
“It’s Déjà vu all over again”. Some famous American said this - probably a politician - I’m not sure. In any case, this panel is a metaphor of the original and can only be detected by the obvious cosmetic perfection - better finish than the factory ever produced I would say. Comments from listeners were on a par with those from the tests conducted with Stewart’s panel. In short, we couldn’t tell the difference. Regurgitation of those comments would be fairly futile since (again) no one could identify either the stack that the test panel was in, or the single speaker that it was in or any anomalous sounds in the system. I am sure that Stewart and Wayne use different coatings on the panel diaphragm and apply it differently, but I cannot hear any differences that I could remark upon, full stop. After a total of 6 months of testing I am sure readers of this little essay want to hear reams of prose regarding the “sound” of this panel but I can only oblige by saying it sounds like an original Quad panel.
Sheldon Stokes, New Mexico, U.S.A.
Not again! Another panel that is impossible to distinguish in listening tests from an original, and that’s about it, really. The output is on par with the original. The upper frequencies are as near to the original as you can get and the openness and tonal quality of the panel is pretty much as an original also. Some listeners in other places have commented that panels from this rebuilder have a slightly harsh quality about them, but I cannot honestly detect that, nor did any listener that heard it in the stacked or single systems. This is another panel rebuild that you can confidently place with an original panel that’s up to spec and hear no difference. It goes without saying that it may sound a little forward and definitely louder if in a system that has older panels that are not in specification. The sound of this panel demonstrates again that coating on the diaphragm has little effect on sound quality as it is different from both Penketh and Picquet panels.
One feels like the trainee journalist who was sent to the Royal wedding and returned to tell his editor that there was no story because the bride didn’t show up! Well, in a sense, the lack of story in some respects, is the story. We clearly have two groups of panels in this Gang of Five. The new panels, as opposed to rebuilt, are definitely “odd” compared to the rebuilds. Knowing the care and attention that One Thing Audio and Quad Germany put into producing their panels and the fact that Quad Germany have the original Quad manufacturing jig I have to look at material factors such as stator construction (later). The new panels are not suitable side-by-side substitutes for the original panels and you will have to buy two of them if you wish to keep the speaker in tonal balance. The One Thing Audio panel will require extra modifications to be done to your speakers for best performance and that is best dealt with by One Thing Audio. I don’t think a One Thing Audio panel is really a proposition for the enthusiast DIYer to install, as it will not give the original speaker the original tonal balance that the owner has come to expect. A suitable result could only be had be having One Thing install their panels and their transformer mods for you.
The second group of panels is clearly the rebuilds from the various “amateurs” around the world. I use the word “amateur” in the kindest sense since it is clear that these panels are the “closest approach to the original Quad” (says he, stealing a phrase from Lord Gowrie). Any of the Penketh, Picquet or Stokes panel rebuilds will do justice to your original Quads in the sonic sense. As an overall product the top dog panel is clearly from Wayne Picquet who gains the accolade for his absolutely fiendish attention to the cosmetic appearance of the panel as well as the sonics. In this respect, Wayne’s panels surpass the commercial offerings by a wide margin. Stewart’s panel being equal sonically in all respects is only a very small margin different cosmetically, and since it is not visible in the average speaker, then this is not of consequence to most owners I would think. Sheldon’s panel is again, the equal of the other three rebuilds in sonic terms and his is also the grand original restoration after all, to whom credit must be given for stimulating this modern renaissance in Quad panel rebuilding. The same caveats apply to cosmetics but as noted above, these may be of little consequence to many owners using them in the original housings.
What a situation! Five to six years ago we were lamenting the lack of reliable Quad rebuilds and panels. Now, there is a real choice, and the choice is yours. Choose then.
New Panels sound quite different to rebuilds of older panels. The major material difference between the two groups noted above is the thickness of the stators with older stators being 2 to 2½ times the thickness of the new circuit board type stators. Diaphragm materials and coatings (within reason) do not make as much difference to the sound of the various panels as one would think. All the panels in this listening test were employing either 3-micron or 6-micron diaphragms and a variety of coatings. It was certainly not possible to pick one panel from another on the sole basis of coating used as the three rebuilds demonstrated. Why then do the new panels sound so different in spite of the use of the original Quad jig in one case for building the panel?!
I have a strong suspicion that it is the thinner stator that is causing a number of the anomalies that we have noted both electrically and acoustically in these new panels. The capacitance of the panels indicates that the difference in materials and the lower bulk of material is having a significant effect electrically, and I believe this translates into the acoustic performance of the panel also. We can dissect that acoustic performance into to two major parts as well. There is an acoustic performance directly related to the capacitance of the panel (an active acoustic by-product) and an acoustic effect related to the extra flexure in the thinner panel material (a passive acoustic by-product).
The latter acoustic effect due to mechanical flexure of the stator would be worth investigation along with the added effect of increasing /decreasing the “tunnel” length of the perforations in the stator. The anomalies exhibited by both new panel builds tended to be in the upper-mid and high frequencies and this cannot be entirely coincidence, given the vastly different manufacturing methods used. There is probably some high frequency resonance absent in these panels when compared to the originals that makes them sound “soft” and seemingly to have less transient attack. The lack of overall output efficiency I would tend to lay at the door of loss of mechanical stiffness in the stators themselves, as a lot of the calculational premises involved with the original assume a rigid stator. In the modern panels I do not think the stators are sufficiently rigid. This is bound to affect the uniformity of the electrical field enough to make some difference, and I say, for now, that it is audible. To demonstrate the proposition, or refute it, we clearly need someone to produce a modern stator from circuit board material that is of the same thickness as the original Quad panel. Any takers?