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Krell FPB 600c 700cx 400cx Heatsink noises.

In 2001 I bought my complete new Krell cast music system: Krell FPB 600c amplifier, Krell KCT preamp and Krell KPS28c cd-player .Siltech cast interlinks. Speakers are JM Lab Utopia with Transparent ref.XL loudspeaker cables. However I certainly have the feeling that all the manufacturing dollars have been spent on sonically critical design elements,there is a mechanical problem,which is bothering me since the moment of purchase.Two or three times during a listening session the metal construction of the heated amplifier cabinet in operational mode makes a sound (tsssjakkk).Probably because the difference in heat of the heatsinks and/or heavy gauge alluminium chassisplates. When I bring the amp in stand by position after listening,this mechanical sound is there also ,several times. I phoned the Krell service department in 2002.Irving Gross told me that it was a diffraction problem.(traction and contraction of the heated amplifier cabinet.) The service department advised me to tighten all the bolts of the heatsinks. It did not help. During the upgrade from 600c to 700cx,end 2002, I told the German importer about the problem. He admitted that this diffraction problem was a tough one to solve.I had the hope that the problem would have been gone after the X-Upgrade but unfortunately it did not. In the english Hi-Fi News magazine of december 2005 (page 28/Howard's Way) I read an article about a former owner of the Krell 400cx."I sometimes got noise from the heatsinks through heating and cooling." He finally could not live with it and sold the amp. My question is ;does anyone has the same problem with this Krell FPB amplifier(600c,400cx or 700cx)? More important, which owner has a smart suggestion to eliminate this undesirable mechanical'vibration'. Otherwise...I figure I have to live with it, which I can because I simply love the sound of my complete Krell cast system.
paulinemarcel8390

Showing 3 responses by sprbggr

sprbggr
32 posts
 
Hello,

I had an FPB600C and had the same problem. It did not disturb me. For the first one or two hours you hear some pop sounds for every 15-30 minutes. After that is was quiet but after switch off it started again when cooling down.

Now I bought a new FPB700CX and this one does not have that problem. So Krell did something with the heatsinks.

However it was never a problem to me. You hear when the amp is getting warm and when the pop sound stops you know it is warmed up completely. Of course leaving it on all the time will solve this problem but costs a lot of energy.

Peter
sprbggr
32 posts
 
I use an Audio Research Ref 3 tube preamp together with a Krell FPB700CX. No problems at all. The new tube preamps all have a DC offset which is only microvolts.

The Krell amps are DC coupled and if your tube amp has a DC offset if will pass through the Krell directly to the speakers. Putting a cap will prevent DC to pass. This is the reason that the caps are introduced to prevent DC to pass.

If you have a good voltmeter you can measure the DC offset of your tube preamp. But is should be close to 0 so I gues with the modern tube preamps there is no problem for this.

Peter
sprbggr
32 posts
 
Hi I did do nothing to my FPB700CX. It just works fine. The LS-25 or 26 will also work without problems. The Krell will for sure not go broken.

Well I know there is a lot of anti Krell crowd but their power amps are world class. I had Classe, Levinson, Pass, Chord ad many more. Nothing even comes close to the FPB700CX. The new Krells sound very sweet in the midrange and have a very controlled bass. Also it is just very enjoyable to listen. Also their CD players and preamps are very very good. I had KCT, KPS28C, FPB700CX together and the sound is close to perfect. But the Wadia 581 + Audio research Ref3 is still a little better tha KCT + KPS28C.

Other amplifiers are good as well but to my taste I prefer Krell.

Peter
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