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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
microstrip
180 posts
 
A friend of mine has an FBP600 that has the same problem, but only a few minutes after being switched off, so it is not disturbing at all. Your (tsssjakkk) really describes the sound it emits!
Years ago I had a Jeff Rowland Model 8 that had the same problem - the solution was just the opposite - I fitted some nylon washers in the bolts and did not be over-tighten them. It solved the problem completely. But as the case structure of the Model 8 is quite different from the FPB one, perhaps the receipt is not adequate to your amplifier.
Anyway if you choose to tighten the bolts of your amplifier you should do it at the correct temperature and in a selective way - the noise means that some mechanical energy - tension - is released very fast - if the parts are allowed to move slowly there will be no noise. It is a question of knowledge or luck - but as most Krells do not have this problem yours should be solvable.
rmrobinson1957
57 posts
 
Hello,

I have a 400cx and it does make that thermal expansion sound - almost like pinging the heat sink with a small mallet. I talked to Krell a service tech who told me essentially the same thing he told you, thatÂ’s "normal" operation. He also told me that they had a fix; send the amp back to them and they apply some kind of tape to the heat sinks. I don't know how effective this is. He did not mention tightening the heat sink bolts.

I decided to live with the occasional ping as opposed to shipping 110 pounds of amp across the country.

If the sound really bothers you could contact your importer or Krell directly to find out more about this fix.

Bob R.
dbld
297 posts
 
My pinging stops once the amp is warmed up [300C]. It pings a couple of times upon warm-up and cool down though. It's no big deal to me...it kind of lets me know when it is good to go...
rmrobinson1957
57 posts
 
Hello,

Microstrip, out of curiousity, I assume you put the nylon washers between the bolt head and the fin and not fin and the structure of the amp. Did you notice whether the amp ran any hotter?

Pauline, I think we all would like to hear how you fare with this.

Good Luck.
Bob R.
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
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