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
I'm glad to see this discussion. My Krell FPB 300 (not c or cx) was quite noisy. Whenever the music got softer for a bit, I'd hear the ping (or as I called it, klink). I figured that loosening all the bolts would help and was surprised when when a former Krell technician didn't agree and suggested thermal tape instead. I virtually fixed the problem by removing the top cover completely. Many of the top cover bolts were extremely tight, overtightened for sure, and I wouldn't have been able to loosen them without a Wiha handlebar style Torx driver. However it looks like amp should not be moved without replacing top cover since it is necessary for mechanical integrity. Now that I've discovered this thread, I may try loosening all the bolts, though I was afraid of doing anything that might affect output transistors. But right now, I've had one channel go bad anyway, might try that before shipping to Krell for repair or upgrade.
My Classé amp once started making a single, loud metallic ping sound whenever it was powered up. It turned out I had torqued the screws holding the top cover too tight after giving the amp a checkup. Loosening them a tad bit solved that issue.
I bought 2 300Cx back in 2003 when I was on assignment in Singapore to drive the Infinity Beta. One of the amp had this noise about an hour into listening. I called the Krell dealer in Singapore Ultralinear about the problem and they did nothing to solve it. They told me it was caused by separate construction of the amp main body and the heatsink. When the amp heated up the heat caused the metal parts to expand. I had been a loyal Brell since the 80s. I gave up completely on Krell after the 300Cx.
I owned the 400cx and now own the EVO 402 and have never heard a peep out of either amp. I listen to all kinds of music, leave the amp on all the time, listen loud, listen soft, listen to the TV/dvd (sometimes, opera mostly).
Those amps have never done anything but make music. My listening room can get warm or be cool so I am surprised that my experience is different from many on the list.
The noise is more common to the earlier runs of the FPB series Hunter. The later issues had sound deadening washers added.