Anyone know about BBC LS3/5a's?

Hi Gang,


    I have been borrowing a pair of 31 year-old Chartwell BBC LS3/5a's this week. I have fallen head over heals in love with them. I don't think I could mix on them, but as a reference they are phenomenal. They also serve a fantastic role whilst editing and comping vocals for example. There is SO much detail at a quarter the (low)volume i generally work at with NS10m's. I find the whole experience a breath of fresh air. I can purchase this pair from my colleague's father, but they won't be cheap, since he knows they ar fashioned from pure unobtainium. I have been questioning the sense in buying 31 year-old speakers that seem to have scant spares available, but common sense does not have much sway in this arguement.

  I have a few questions, if anyone has any knowledge. I have a pair of spare KEF T27 tweeters, but they seem to be different to the ones in the Cartwells, which have a metal dispersion grill. Is the basic tweeter the same? Can I remove the grill, and stick it on to the new tweeters?

  The B100's in the Chartwells, are they the same as regular T100's, merely selected complimentary pairs? Is the construction different? How big a compromise would it be to use a B100 from, say a constructor series KEF monitor? Are we talking incremental or radical differences in driver response?

  Time for a longshot, does anyone happen to have any spare drivers for sale?



    Kindest regards,



      ANdyP

I can't give much advice regarding spares, Andy, but I can say that I've used the Harbeth LS3/5s at work (we have custom active versions) and they sound awesome. The detail was amazing, particularly what you can hear ambience/space-wise. Very realistic. Yes, the bass response doesn't go down to DC, but the sound is undeniably very good.

Maybe you should try some LS5/8s...... A bit big for some spaces though maybe.

Thanks, Roddy,


  I concur with the comments about ambiance! extraordinary detail . . .. the bass doesn't go very low, but is a very gradual drop-off, and there is plenty of information down there, even if it is a bit boxy. Anyway it is the stunning midrange and top that entices!


    I actually want little speakers, so i have to keep the volume down! There is nothing wrong with my hearing, amazing considering 25years of studio life, but anything that means I keep the volume down has got to be a good thing. I am now 43, and intend to be be doing this til I drop!

      Kindest regards,


          ANdyP

   

I had two sets of home made ones, though one was unfinished and had teh cheap crossovers from the Kef contructor series. A random choice left an ex-girlfriend with the ones with proper crossovers from Falcon accoustics, (at the time they sold all the proper parts).

Here are a few links. the little grille is said to be important, as is the felt surround for the crossover.

http://www2.kef.com/ca/about/ls35a

Original BBC design paper - "the Horse's mouth"
http://downloads.bbc.co.uk/rd/pubs/reports/1976-29.pdf

Even has an unofficial support site
http://www.ls35a.com/

Whilst doing some digital audio experimental work in the 90's, (I think), I couldn't keep up with the cost of replacement T27's, (full level 5KHz square waves are very unkind to tweeters), I was lent a pair of Dynaudio PPM2's. they were as much of an improvement over the LS3/5 as they had been over my previous monitors. Really didn't want to send them back, nor the Hill Chameleon Amp that came with them

Unfortunately, stock or replacement B110 woofers from KEF won't work properly. The LS3/5a used woofers specially selected for a particular response in the midrange, and the crossover was designed about that response. Any B110s KEF sold over the counter were ones that hadn't met the selection specs for the LS3/5a.

The tweeters, I think, are closer to stock, except of course for that grille.

My advice, if you buy them, is to drive them with a smallish tubed amplifier. The low power will keep you from blowing the speakers, and the tubes (more properly, the output transformer) will make it almost 100% certain you won't get DC on the outputs, with subsequent fried woofers. I use a Dynaco Stereo 70, modified with bigger filter caps, polypropylene coupling caps, and metal film resistors. Oh, and the 3/5as sound best on the 4 ohm tap.

[Edit: Oh, the LS3/5a has NO magnetic shielding on the drivers, so you don't want to put them next to a CRT monitor.]

Peace,
Paul

hi guys,



  thanks for replies. I am using a MYST TMA3 35W hifi amp from about 1985. Very large power supply for 35W, and happy into any load down to 2Ohms, apparently. I usually use it on my NS10M's in preference to any other amp I have ever heard. LS3/5a's seem to love it, and the idea is to ONLY listen at low volume, hopefully reducing the danger. Guess I am just going to have to be careful!

GENERAL COMMENT, using a small amp will NOT protect you from fryouts, since it is clipping that normally puts paid to most drivers, esp tweeters. A large amp at the same volume will give you added protection against clipping, since you have more headroom. Just don't turn it up to full power!


    Roddy, are the active LS3/5a's you use at Auntie Beeb of recent constructio? ie do they have original KEF drivers in, or have they been developed with more modern drivers like Monocor Bass, and Morel, Scanspeak or Vifa tweeters?


  Kindest regards,


    ANdyP

Reading this write up about Harbeth loudspeakers, it suggests that they were using KEF drivers, and that is why they stopped making the 3/5s when the drivers were no longer available. The ones we have were very recent and looked new. There's also plenty of old sets kicking about too though. In case you are tempted by the LS5/9 (which was an attempt to recreate the performance of the LS5/8 at much smaller size) I probably wouldn't bother, good though they are. The overall sound seems more coloured, especially in the low-end where I found it a bit unclear. That's possibly because they used a ported design in order to reduce the cab size whilst trying to maintain bass response.

strangeandbouncy said:

  thanks for replies. I am using a MYST TMA3 35W hifi amp from about 1985. Very large power supply for 35W, and happy into any load down to 2Ohms, apparently. I usually use it on my NS10M's in preference to any other amp I have ever heard. LS3/5a's seem to love it, and the idea is to ONLY listen at low volume, hopefully reducing the danger. Guess I am just going to have to be careful!

GENERAL COMMENT, using a small amp will NOT protect you from fryouts, since it is clipping that normally puts paid to most drivers, esp tweeters. A large amp at the same volume will give you added protection against clipping, since you have more headroom. Just don't turn it up to full power!

Click to expand...

While this may be the case with many speakers, it's not the most common problem with LS3/5as. Their power handling capacity is low, and an unclipped 50W amp will cook the woofer. All it takes is one loose RCA cable...which implies, incidentally, that any amp you use to drive LS3/5as shouldn't use RCA connectors! My Stereo 70 has been modified to use 1/4" TS cables, which connect the ground before the hot. Ideally, of course, I'd use XLRs...lots of difficult punching involved there, though.

Anyway, the Stereo 70, running the LS3/5as off the 4 ohm taps, puts out about 20W/ch, which is a nice safe level. Haven't blown a tweeter yet, or a woofer either.

Peace,
Paul

Hi Pete,


    Myst TMA3 gives 35W into 8 Ohms, so @17W into 16 Ohms. Nice and gentle. IMHO Clipping IS an issue with ANY driver, since even at 17Watts, it is effectively looking at DC. 17W from an un-clipped amp is MUCH safer. You get my point, I hope, and I certainly get yours about the very low power-handling of this driver. Running 50 Watts  into this B110 will cause more than overheating, since the coil will leave the gap, if not the building!

    Kindest regards,


    ANdyP