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| the TDL BS2, practically dead, cone tweeter and woofer with no foam, already poor repaired |
Really TDL in 1980 build a bookshelf similar of this one? Reading the label under the binding post we see Model BS2, TDL transducer, Transducer Development Ltd, High Wycombe, Bucks, tel (0494) 35576. The address is exactly the UK TDL old address, also the front stick are the same of the big speakers. Probably this is the mother of RTL1.
One of my friend bought those speaker on Internet, pay a few, but when arrive we see all speaker destroyed. Someone make a tentative to repair the tweeter with glue and the woofer is bended, stay too many days without foam! But none of my friends (heavy audiophiles) see one of these speakers in the last 30 years so the owner and I pass to the restoration.
Under first check, with magnifier glass, the tweeter is original, is a cone with no dust cap, the woofer also is original, a light paper cone with the dust cap not original. All speaker are badly repaired but if we put the 2 box face up and send some mW the 2 cones sound in all frequency :-)
Firstly must be removed the speaker to check inside the box, we find some sponge (with open holes, as usual), green, only 2 cubes in one box. The crossover is not sealed, it stays between the 2 cubes, the quality of wires is good for a small speaker. See the figures of inside.
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| without speakers we can see the 2 piece of sponge, the good wires, on the right the xover unfixed, and a "must" |
I already have see in other TDL speaker this one; I find in one RTL4, in my Studio 4 Monitor, "the date". See the zoom of the above figure on the right, there is a stamp with the date.
In other zoom of the photo of inside a first "strange": the accord tube of bass-reflex. The tube end about 5 mm from the rear side and there is a support near the end, a piece of carton folded as pyramid and glued between the bottom and tube.
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| probably this is the date of the box (E, 17 MAR 1980, F.P. LTD), on the right the tube of bass-reflex |
Put speakers on the table we can see the rear with model and brand? We removed the dust-cover to fix the coil before clean the foam.
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| the woofer is: 6/55P 8 ohm, the tweeter is: 3T/900 15 ohm, unfortunately no brand. On the right the not original dust cover removed |
The woofer have the cone folded and cannot be repaired mounted. If you need not a repair but a restoration we must check, under microscope, the 4 coils, so all speakers are dismounted, see the photo.
3 of the coils are in good condition. One of the tweeter have a bad bind on the wire arriving on the coil, I untwist about 10 mm of the coil and sold a new, very flex, cable up to the soldering pad, after fold the old coil wire and with a drop of glue the tweeter is ready. After check all is ok.
In photo you can see one of the woofer cone restored with Japanese paper (the rice paper or Japanese paper is used for restoration of secular books). Using a special restorer's vinyl glue one piece of paper is sufficient. Also the tweeter was restored in the part of the cone bended to accept the foam.
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| the frame is metal bended type and the hole on the magnet is closed, see a piece of rice's paper |
Only one piece of japanese paper is sufficient to fix a bend on the cone, in the photo some piece of paper glued to woofer and tweeter to obtain a "rigid" cone with only a little more total weight.
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| the woofer restored in 3 points with japanese paper, see the perfect coil |
Find the foam for the tweeter is not easy; in the market exist only some rubber for small woofer with this diameter, but one of Chinese supplier has foam for old cone midrange. Probably is not a moment to discuss about the different type of foam, different compliance, surely all of reader know the 5 type of rubber surround, heavy for large woofer, light for high-midrange.
On the photo the glue used, from an Italian brand of speakers and parts. I prefer to mount the foam on the cone and in the next day mount the cone and the frame.
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| the mounting of the foams on the tweeter and woofer frames using the Ciare YAC902 glue |
The FerroFluid ! I buy some mL of ferrofluid from the foam supplier (you already know about the 4 type of Fefluid and I don't like to add more). If you like to add to a tweeter you must evaluate first a big problem; IT IS PRACTICALLY IMPOSSIBLE TO REMOVE IF SOMEONE WAS WRONG.
I use ferrofluid to enhance the power dissipation of the coil, the better focalise the magnetic field, to obtain more linearity when tweeter reproduce his low frequency, to smooth a little the impedance curve, to ..... . Please check the benefit of ferrofluid on the speaker in books and magazine.
If you like you must use only a few, only necessary to fill the empty among the wires of the coil, only outside, extend in 2 or 3 time to permit to the fluid to arrive inside the coil.
One of the problems of ferrofluid is "the time", if years can destroy the foam can also desiccate the oil of the Fefluid. Also is the coil is fused with a resin (as inside the power transformer) the use of fluid is a fake. Today exist a bi-component resin for speaker coil with inside the Fefluid but only the factory of the cone can use.
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| the frame on the tweeter and the FerroFluid for their coils |
At this point we have the 4 cones ready to be mounted. There are "schools" and flames in more and more forum on the best method to mount and centre the spider and the coil. I sue both the mechanic method with some triangle of paper or cardboard to centre the coil, and also the electromechanically resonance method using a power amplifier, a signal generator to put in resonance the cone for auto-centre.
In the photos the cones ready to be fixed and an example of foam fixing (the pieces of paper in the coil is to not disturb or bend the coil, after I use the resonance method to centre the foam).
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| on the left the cones ready, on the right the fixing of the foam, next day of the mounting of spider |
Finally after days and days the speakers are ready. But remain the problem of dustcover; I never see the original, the woofer have not and tweeter have a poor substitute. Also I think to have more weight on the 4 cones with restoration (rice's paper, glue, ...).
If we use one disk of japanese paper as dust cover? None of the speaker have the hole on the rear to permit the flow of the air around the coil, so use this paper glued only in the circonference to the cone and as-is in the centre reply to the 2 queries, light weight and air flow.
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| finally the cones restored and ready |
Of course there is not in the Internet a schematic for the crossover, Irving M. Fried and John Stuart Wright are dead years ago. The new web site of TDL in UK seems to be frizzed.
Fortunately the xover seem original in all parts and design. With a pencil and a piece of paper is not difficult obtain values and design. The crossover use a PCB as many other UK brand, and the path is large as necessary for the current going to the speaker.
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| the new and old binding pot and the 2 sides of the original crossover |
Measuring the crossover I find a strange design. Fortunately the xover seem original in all parts and design. Returning to pencil and paper and check more the strange design. As already said the crossover use a PCB, all paths are large as necessary minus two.
On the PCB there is space and holes for 12 db/octave filter but components are mounted as 6 db/oct for woofer and 12 db/oct for tweeter. The speakers are all in-phase with binding post. The capacitor is not-polarised.
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| original crossover schematic of TDL BS2 |
The coils: as see in the photo the chokes are in-air and fixed with strip. Restoring I see a glue inside one of the choke, why?
After desoldering and measured (with ZRLC from Nuova Elettronica, Italy) at 1000 Hz the two coil shown 245uH-243uH for the 2 tweeters, and 527uH-529uH for the 2 woofers.
Inside one of the choke there is a very thin iron wire, 3 cm long. I remove and remeasure the choke, 497uH, incredible!
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| one of the crossover and the zoom inside the bass choke on the right, yes it is a piece of iron wire |
Reading from this page "John always wanted the finest performance and was fanatical regarding quality", so is not a surprise find an "accord" of bass choke into a TDL loudspeaker. It is possible make accord with one or more round of wire but also the R-series change, in this case with a little wire of pure Fe (0.3 mm I think) the builder solve the problem.
Do It Yourself? This is one of the case were a father of HiFi speaker can not be reached by a single person, please remember in 1980 at Elac-TDL work John Wright but also I.M Fried, Jim Thiel and Andy Lockwood!
Next step is replacing the capacitor with a new one. I like for crossover the Wima MKS and MKP and the Mundorf M-Cap. You cannot accomplish but I suggest use of capacitor with LOWER voltage values, 100V is better, or 150V if you do not find, in case of M-Cap the lover values is 250V.
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| The crossover with the tweeter capacitor replaced and a little modify, see the text |
Can I make a little calculation? Using a 8ohm woofer/tweeter with 63Vdc, 100Vdc or 150Vdc of swing on the filter capacitor we can calculate:
| capacitor (V) | RMS (V) | R (ohm) | current (A) | power (W) |
| 63 | 22.3 | 4 | 5.6 | 124 |
| 63 | 22.3 | 8 | 2.8 | 62 |
| 63 | 22.3 | 16 | 1.4 | 31 |
| 100 | 35.4 | 4 | 8.8 | 312.5 |
| 100 | 35.4 | 8 | 4.4 | 156.3 |
| 100 | 35.4 | 16 | 2.2 | 78.1 |
| 150 | 53.0 | 4 | 13.3 | 703.1 |
| 150 | 53.0 | 8 | 6.6 | 351.6 |
| 150 | 53.0 | 16 | 3.3 | 175.8 |
If you think to put more then 312W on your tweeter probably is better use a capacitor with more then 100 Vdc. See the currents on the tweeter's capacitor, probably, is better use 2 or more in parallel.
On the photo the rebuild of crossover with some little modify. The capacitor was replaced by two Wima 1uF/63V MKS type, the two small path for tweeter an ground (see upper left corner of left photo) was reinforced with some Sn soldering. We add also a small copper wire (as a bridge) from the input black negative and the negative path the obtain lower resistance on the PCB.
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| The modify on crossover, see on the photo for description |
From years when, with my hobby, restore a crossover I use the wax, paraffin stock, for fix all components, surely is not a my idea, you can see on Quad, Dalquist, Beveridge, old Magneplanar, and more.
Better is use a large pot with wax stored in an electric oven with a good temperature control. Be careful to not reach the max temperature of capacitors, often 85°C, and submerge the whole PCB in the pot for almost 3 times. In the first time you can leave for half minutes inside the liquid wax to permit to wax to reach every hidden point, as inside the choke, after cool the next step must be fast, seconds, to not remove the previous wax.
For the internal wires I like to reuse the original. As previous described the binding pots are replaced with a new one able to accept banana, fork, and single wire.
The old sponge was replaced, in the hands she seem to have the same problem of old foam. Was replaced with the internal fill used in top quality speaker, white, in foils (similar to foils used as filter in some HVAC). Foils by foils I filling all available volume with the crossover suspended in the middle.
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| The new internal absorber and the speaker with the tweeter fixed reusing the old wood screws |
I'm working for this section, I like to measure the impedance with my ZRLC meter and the frequency response in free air.
Fortunately a friend of mine has a registered version of TrueRta and using the "chirp" I can estimate the response of the speaker. But to be accurate you must use a power amp able to go down up to 2 ohm. It is not necessary a big power, 5W on 8ohm are sufficient but important is the frequency response in any load and the Current-Voltage characteristics.
I pass the speakers to my friend, Maurizio P., owner of Audio Research components, and wait some weeks to obtain a review, the following:
The main shortcomings of the TDL BS2 in my opinion are: low efficiency and extreme treble frequencies level is a bit lower than desirable, at least for my tastes. Fortunately the strengths are more than the weaknesses, starting from bass frequencies incredible by extension and sound pressure, considering the size of the box and the small cone of course, midrange tones are excellent, especially voices are awesome, among the best I ever heard, the stage is not very wide but unexpectedly accurate, finally the detail level is satisfactory.
I think using them with some brilliant SS amp should give great performances on several kinds of music, provided that your favorite genre is not the hard metal, surely better suited for small groups or soloists, especially with acoustical instrumentation.
Returning, I pass the speakers to one other my friend, Rolando, owner of Audio Note equipments, and wait some weeks to obtain a review, the following:
Une véritable surprise entendre les mini haut parleur TDL BS2 restauré par l'ami Gianni. Gianni a vraiment fait un travail minutieux er précis. Un mini haut parleur par le son vraiment très equilibre. Avec un haut de gamme et milieu de gamme comme un vrai mini monitor (voir Rogers LS 3/5a). Certes, le bas de gamme, ayant un woofer de 14 cm seulement, fait son travail honnête, mais le bas de gamme est cependant encore très satisfaisante, plus avec le cd que avec du vinyle, mais il suffit de tirer les mini haut-parleurs au mur, pour ameliorer la situation sonore.
Il est vrai, comme je le disait, avec le son du CD l'écart (le gap) .... semble moins evident. Nous entendons immédiatement que la haut de gamme e milieu de gamme sont véritablement super ... soit avec la musique classique que avec le jazz. Elle souffre logicement avec le rock, mais c'est ... naturel. Cependant, un grand son avec la musique acoustique, vous devez entendre, par exemple, le vinyle "Bert and John" de Bert Jansch et John Renbourne deux guitaristes (acoustiques) formidable, il semble de le voir jouer la en face de vous.
Un son claire et net qui vous frappe et très remarquable. Et rappelez-vous que les haut-parleurs ont été restaurés récemment. Alors plus ils travaillent plus ils améliorent. Bravo Gianni un excellent travail technique complet. Rolando.
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Donations if you have not a Bitcoin wallet
If you like this work and measures you can make a small donation of Bitcoin. You do not need a wallet to make a donation, indeed even those who have Bitcoin wallet is better to pass for a web site that "gift" currency since this does not have a transaction cost.
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| In the last years at Universita' Degli Studi di Roma La Sapienza |
Dr. G. Visco already contract professor for Chemistry in Environment & Cultural Heritage into --> |
Corso di Laurea in: Scienze Applicate ai Beni Culturali ed alla Diagnostica per la loro Conservazione |
