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Krell FPB 600 VS Krell Ksa 300s?

Infinity!

Infinity!

Well-Known Member
Hey guys, I have been looking the past year for a local option to buy a Krell KSA 300s for my Infinity Kappa 9's, but have had no luck so far. However, a Krell FPB 600 popped up in my area and I am interested in the sound differences between the two different lines of amps. Forgetting about the shear amount of power difference (300 watts into 8 ohms vs 600 watts into 8 ohms), has anyone here actually heard the differnece and/or know the different sound characteristics? According to the manual, the KSA is rated to 1 ohm while the fpb is rated to 2 ohms... why is this? Any and all help is extremely appreciated. Thanks!
 
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Both will drive Kappa 9's just fine Major differences are that the KSA is older, the FBP is a switching amp, whereas the KSA is pure class A. Pure class A drinks a ton of juice just at idle and can heat a room, even at idle. The FBP will generate a lot less heat under most conditions, and consume a lot less electricity.

I have 4 KMA 160 monoblocks--pretty much identical to their KSA (stereo) counterparts. Each one draws 8A current at idle and you can cook eggs on them after an hour of operation (even at idle).
 
savatage1973 said:
Both will drive Kappa 9's just fine Major differences are that the KSA is older, the FBP is a switching amp, whereas the KSA is pure class A. Pure class A drinks a ton of juice just at idle and can heat a room, even at idle. The FBP will generate a lot less heat under most conditions, and consume a lot less electricity.

I have 4 KMA 160 monoblocks--pretty much identical to their KSA (stereo) counterparts. Each one draws 8A current at idle and you can cook eggs on them after an hour of operation (even at idle).
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I assume you're talking about the "Sustained Plataue Bias II" when you're saying that the fpb is a switching amp and not a true class A. But when I read the manual for the FPB, it states that the "Sustained Plateau Bias ii is a true Class A circuit as opposed to sliding or adaptive biasing schemes." Can you elaborate a little more? I'm just curious if there is something you know that I dont (as I am relatively new to krells)?
 
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An FPB600 could turn your 9s into ashes ... Even still, that's the one I'd buy. You just never see 'em for sale ...
 
At one point in life I had a FPB300 and an FPB600. The FPB600 is special - won't go wrong with one of those and you'll not regret it.
 
Infinity! said:
I assume you're talking about the "Sustained Plataue Bias II" when you're saying that the fpb is a switching amp and not a true class A.
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Yes, that is what I was referring to. I guess I could have made myself clearer, but most folks don't understand that concept. Most pure class A amps pretty much run wide open even at idle, which consumes a lot of power and generates a lot of heat, but the FBP is kind of a unique design, and far more efficient. I did not mean to imply that it was an A/B design.

The only reason that I have the KMA 160's is that FBP's rarely turn up for sale in good shape and at a reasonable price, and I found the matching quad of KMA's from the original owner at a very good price, and in great cosmetic/functional condition. You'd figure that in these price brackets people would take better care their gear, but 90% of the expensive Krells that turn up for sale have bent heat sinks and scratched up faceplates and handles. I realize that they are big and heavy and awkward to move around (mine haven't moved since I bought them over 10 years ago, and aren't going to anytime soon), but you'd think people would be more careful with them.
 
If the FPB hasn't been serviced, keep that well in mind. If it doesn't already need it, it will in the future. Service will almost certainly involve shipping that the mailman can't handle.

The nice thing about the FPB's is that if the fone or doorbell rings, and you get caught up in a 45 minute conversation your amp doesn't continue heating your listening space at full tilt BTU output.
 
bowtie427ss said:
If the FPB hasn't been serviced, keep that well in mind. If it doesn't already need it, it will in the future. Service will almost certainly involve shipping that the mailman can't handle.
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I 100% agree, but the KSA is in the same boat, if not worse--it is older and runs at "full tilt" heat production even at idle, At least the FBP "takes a break" from being a space heater if not being run hard, and still a "back-breaker".
 
My KSA has a bent heat sync. It is almost unavoidable when they get shipped in non factory packaging. As to space heater status. It heats my basement listening room nicely in the winter.
 
Okay, so after reading your guy's responses, I think I will at least go have a listen to it and most likely purchase it in the next week or two. My only question that I still have is if it is stable to 1 ohm? I messaged krell and they stated that they wouldnt push it too far past the 2 ohm mark which is weird because most of there amps are at least rated to 1 ohm.
 
Infinity! said:
Okay, so after reading your guy's responses, I think I will at least go have a listen to it and most likely purchase it in the next week or two. My only question that I still have is if it is stable to 1 ohm? I messaged krell and they stated that they wouldnt push it too far past the 2 ohm mark which is weird because most of there amps are at least rated to 1 ohm.
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I suspect that they would be willing to rate it down to one ohm if it where serviced. If all original, it would be hard to certify that level of performance without having seen the amps condition.
 
Infinity! said:
Okay, so after reading your guy's responses, I think I will at least go have a listen to it and most likely purchase it in the next week or two. My only question that I still have is if it is stable to 1 ohm? I messaged krell and they stated that they wouldnt push it too far past the 2 ohm mark which is weird because most of there amps are at least rated to 1 ohm.
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I would say YES--it is 1 ohm stable, but not for continuous operation at high levels at a steady 1 ohm load--and for marketing purposes, it probably cannot achieve that true "double down" rating going from 2 to 1 ohm like they proudly advertise for the KSA/KMA series. The manuals for my KMA monoblocks even state that the protection circuit can be tweaked to operate below 1 ohm. If you review the manuals more carefully, you will note that the power/impedance ratings are for continuous RMS ratings--not "peak power" or "minimum operating conditions".

I know where your concerns come from--I have Kappa 9's--at one point I had three pair of them (I have also owned Apogees), and I know all about the impedance dips below 1 ohm, but they are not a continuous 1 ohm load. Before I bought my Krells, I ran them on a pair of Aragon 4004's--which are only rated down to 2 ohms, and they never broke a sweat--even when pushed hard.

Either the FBP or KSA will work just fine--you are "overthinking" this.
 
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