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lamepops1
02-08-2004, 07:40 PM
For the past two years, I have been struggling with a problem in my system that causes the hf drivers to be blown in my KEF Q55.2 loudspeakers. My dealer has been extremely patient through all five (!!) repair cycles, and shortly I will be receiving a brand new pair of 2004-model KEFs to replace the Q55's. Unless I find a problem, I will be selling the KEFs because there is no reason to suspect they will not be damaged similarly.

Some of the things I've done to get around the problem....

- replaced my power strip with a line conditioner (now using Tripp Lite 600W)
- replaced my receiver with separate preamp/amp (Adcom 555-II)
- replaced my cd player (now using Rotel)
- replaced my cables (short matched-length monster cables)
- borrowed an oscilloscope, bought an audio test cd, built a dummy load, and spent a couple weekends trying to get my system to break or display some sort of clipping or distortion.
- hooked up my old Large Advents and a pair of old Technics loudspeakers at volumes approaching insanity, and no problem
- moved the system to different rooms (blew the driver in 3 different locations)
- took my entire system to the dealer, and demonstrated that it could be played at mind-numbing levels without any problems.
- ran the KEFs on my dealer's Mcintosh 400w/ch system, and they perfrmed flawlessly.

It seems to point to an "environmental" problem....but I am out of ideas at this point. I know there are Adcom haters lurking...but I have blown the KEF drivers in 3 setups now...first with an Onkyo AV receiver, then with a Carver receiver, and finally with the Adcoms.

Any ideas or suggestions would be appreciated.

mtrycraft
02-08-2004, 09:55 PM
Some of the things I've done to get around the problem....
- replaced my power strip with a line conditioner (now using Tripp Lite 600W)
- replaced my receiver with separate preamp/amp (Adcom 555-II)
- replaced my cd player (now using Rotel)
- replaced my cables (short matched-length monster cables)

None of these have an effect on the tweeter


- borrowed an oscilloscope, bought an audio test cd, built a dummy load, and spent a couple weekends trying to get my system to break or display some sort of clipping or distortion.


Good move. Any results? Of course it is not blowing when you are looking :)


- hooked up my old Large Advents and a pair of old Technics loudspeakers at volumes approaching insanity, and no problem


Interesting.


- moved the system to different rooms (blew the driver in 3 different locations)

Not good :(

- took my entire system to the dealer, and demonstrated that it could be played at mind-numbing levels without any problems.


Did you take your amp that drives the kef? Is it able to handle such a low impedance load?
Does the tweets blow on any music or movie or just one or couple?



It seems to point to an "environmental" problem....but I am out of ideas at this point. I know there are Adcom haters lurking...but I have blown the KEF drivers in 3 setups now...first with an Onkyo AV receiver, then with a Carver receiver, and finally with the Adcoms.

What does the dealer or KEF has to say on this? Did you call KEF?

lamepops1
02-09-2004, 08:17 AM
"None of these have an effect on the tweeter"

I was upgrading components based on feedback from the dealer that I was feeding the KEFs crap.

"Good move. Any results? Of course it is not blowing when you are looking "

I posted somewhat extensive test results on the diyaudio site (search for Lamepops if you want). I checked several frequencies between 100 Hz to 16 KHz at 1/4 and 1/2 volumes with no signs of distortion (did the same checking with actual music). I also put my 8-ohm dummy load in parrallel with the old Technics speakers (to simulate 4-ohm operation), and ran the volume up to 3/4 (!!) and saw no sign of distortion.

"Did you take your amp that drives the kef? Is it able to handle such a low impedance load? Does the tweets blow on any music or movie or just one or couple?"

The exact setup (my Adcom amp, my KEFs, everything) performed flawlessly for over an hour at the dealer. It took less than 5 minutes to damage the KEFs at 1/4 volume in my home. That's why I think it is environmental. I only use my system for music...and I listen to lots of music...from old Genesis to Type O Negative.

"What does the dealer or KEF has to say on this? Did you call KEF?"

I have been told from the very start that I needed to provide more clean power to drive the KEFs, and this was reinforced by the dealer's demonstration of my KEFs on his Mcintosh system, operating between 40 and 400 watts. It was really f****** loud...much louder than I have ever played them. I have not spoken with KEF directly, and the dealer has mentioned that this would be the last repair/exchange for free. That's why I'm going to sell them....because I have not found the root cause. I am supposed to be receiving a brand new 2004 model this week.

kelsci
02-09-2004, 10:39 AM
Lamepops; perhaps in some freaky way, DC is being produced within the system. Usually that would be with the power amp section of a receiver or amplifier. A real longshot is that somehow AC is being turned into DC within the speaker's crossover destroying the drivers.

skeptic
02-09-2004, 11:40 AM
Intermittent problems are the toughest and most frustrating to find. They never seem to show up when you are looking for them and you are often never sure when you've solved them.

There are several possible causes. The most likely is a parasitic signal just above the audio passband getting into your amplifier or preamplifier. This could be caused by a defective source component such as a cd player, radio tuner, or tape deck, radio frequency interference, or spontaneous oscillation of the output stage as would be caused by high capacitance speaker cables. You have already ruled out the amplifier and preamplifier by replacing them. Do the tweeters on both speakers blow at the same time? If they do, then you can rule out the speakers themselves. If they do not and only one speaker fails at a time, then the likely problem is a defect in the crossover networks. A bad batch of capacitors which found their way into a production run and which fail intermittently would cause just such a problem.

lamepops1
02-12-2004, 10:34 AM
I finally received my Q55 replacements from KEF....the Q5. I've been told by the dealer that they have a more rugged hf driver, but I am not going to chance it. I have not really isolated a problem, and have exhausted my money and time. I'm not even going to open them up, and sell the Q5's and try moving to a different speaker.

I finally spoke with someone who seemed to understand my problem very well...an Adcom/KEF repair center in New Jersey. The director of tech support there told me that while the KEFs are sonically very pleasing, there are somewhat "delicate" and more of a finesse speaker than I am looking for. In essence...I really am just over-driving them, and that there is no mysterious system instability issue. Anyway...I've replaced everything else, so might as well try this.

It's hard to ignore the Axiom loudspeaker ratings here on this site. I am considering the Axiom M60ti. Considering I like my music loud, are than any other good matches for my style/price range?