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Checking drivers in LST


Kev_Rat
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I have been using my LSTs now for a couple of years now.  They are driven by a pair of Krell-KAS with a Burson Conductor 3XR providing preamp and DAC duties.  Of late I have been worried that the tweeters have been getting old and I also felt that one side was down a little as the stage seemed a bit to one side.  On the basis of never having enough spare drivers I have managed to collect 4 rebuilt tweeters and half a dozen very nice 200010-1 mids so time to test and replace any weak ones.

Listening to the speakers, all drivers seemed to be working so I tried some cardboard tube to hear if any were down.  About this point I realized that my ears were not up to this task and I just get confused so I broke out a sound meter and ran some measurements.  After a bit of faffing about I created the attached set of measurements using a web based tone generator at a set volume.   I measured twice and then swapped the speakers R:L, to check the amps were not an issue, and repeated.  The measurements were all pretty repeatable and close, which was rather reassuring.  The measurements were made with the Balance Level set at 1 and the results are an average of all samples.

It seems to me that I could replace all the mids in L speaker and Tweeters 1,2,4,5 going from L to R then measure again.  I could barely hear the 14,440Hz tone so the hearing isn’t as good as it was once.  The speakers are currently front wired and while the tweeters are the same, the new mids are rear wired.  So a little work to do there.  I will obviously need to send the tweeters I remove off for refurb (once shipping from Australia improves) to keep some spares for the future.

Comments and advice would be appreciated before I go berserk on the soldering Iron.

Regards1999655474_LSTMeasurements.thumb.png.0bc18f6618c06a24074a804064cf5b21.png

Kevin

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  • 4 weeks later...

Hi Kev,

Did you get a reply to this?  I am no expert so will not try to answer your question.  I am enjoying my LST-2 right now listening to Men at Work Cargo vinyl.  Chris V rebuilt all six of my tweeters.  Alternately I have ESS amt3 rock monitors and ESS amt1a pyramids.  For some time I thought the ESS were better sounding, but as either I’m getting used to the LST-2 or they are breaking in….I like these enough not to put them up for sale.  The ESS are not going anywhere either.

BBE3B74A-B2A1-4B47-A5CE-56CFC767B960.jpeg

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No, not yet, so still not sure if my measuring approach is good.  I tried the cardboard roll, but that was hopless except for basic y/n does a driver make sound.  In any case, as soon as I get some quiet time, I will get onto some swapping and soldering and measuring - gently and carefully.

I agree, in terms of letting go, it can get hard.  In particular, the LSTs will work their way into being kept, because they start off ok and get much better with a little time.
 

 

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  • 2 weeks later...

In regards to the fuses.....what exactly is the issue or issues?

I know the fuses can internally increase in resistance.

Do the fuse holder clips, attaching hardware and ring terminals (on the inside) develop resistance due to corrosion?

Seems they could but I wonder whats been proven.

Is an alligator jumper across the fuses suitable to eliminate the known concern?

This would be important info for the OP........

 

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On 11/1/2021 at 9:54 PM, ar_pro said:

If you don't do anything too extreme with your signal gen & amplifier, why not just remove the fuses, jumper the connections, and test them that way?

Absolutely! In fact, if you are not pushing the speakers hard and have a reliable amp, you can use them with jumpers until the fuses are replaced.

The fuse is the issue, not the fuse holder. It develops very high resistance due to internal degradation.

Roy

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Great advice and thanks all

A couple of pair of correct replacement fuses has arrived after a long journey (Thanks Larry) and it gets interesting

The fuses in situ were 40amp whatever nondescript items.  So effectively speakers were jumpered, so I guess I have not been pushing them too hard. 

Replaced and now to re-measure and think

Kevin

 

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