If your 2.4s are new, then you will need the better part of a year to properly break them in. I speak from first hand experience with these fine speakers and it took me that long playing them for a couple hours a day. They simply need break in time. Your Krell should be ample power to properly drive them; I use a 45 wpc CJ CAV50 and love the sound, though some Audiogoners here don't believe this is possible. Also, here's another "throw you for a loop," I replaced my Harmonic Tech speaker cables with Mapleshade Single Helix cables and these are by far better in dynamics, smoothness and extension than the HTs. Just keep playing those 2.4s and they will continue to improve!
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IMHO, the Krell KAV's aren't really true Krells. They're geared for inexpensive home theatre as opposed to the other Krell power amplifiers that are geared for serious audio systems. If you like what the Krell KAV is doing, I think you'll find the better Krell power amplifiers a pleasant upgrade. They work well with Thiels.
I drive my 2.4s with ARC's Ref 110 power amp but in your price range I would stay with high quality SS from Krell/Simaudio/Pass Labs. Here are some options from the Agon listings that I think will be very good with your 2.4s in your price range of $1,500-$2,500:
http://app.audiogon.com/listings/monarchy-audio-se250-hybrid-power-amplifier (These are interesting with 250wpc into 8ohms and 500wpc into 4ohms w/ first 50wpc biased in Class A)
http://app.audiogon.com/listings/mcintosh-mc7270-power-amp (Not familiar with this McIntosh amp but looks like it might be a good deal)
http://app.audiogon.com/listings/krell-ksa-150-class-a-amplifier (150wpc of Class A Krell power. Given age of this amp, I would check the caps on it)
Hope this gives you some ideas to research.
Thanks for all the recommendations. The Krell KAV does have more power than I truly need (yes, nice to have headroom, but still...) and it is extremely neutral, maybe too much so with the Thiel's.
I'd love to mate them with a big McIntosh, but that's not going to happen... (too much $).
I've also looked at Mark Levinson's... I've heard the 2.4's with a 336 a few years back and that was breathtaking. A 334 should fall within my budget.
The Krell KAV's have plenty of power above 4 Ohms, below not so much. Those Thiels of yours go below 4 Ohms quite a bit.
Be sure to read the current thread on Levinson before purchasing one. If you like Macs and Levinsons you might want to consider Ayre, Classe, Electrocompaniet, and Clayton. FWIW, my tastes run more to Krell and Pass with Thiels.
Ok... The Mark Levinson No334 is a major step forward. Mind you, the Krell isn't bad, just a little too forward for the Thiels. The biggest difference is really how relaxed the Thiels now are.
Used to have Magnepans and I would bet that the roles would be reversed with those speakers... the KAV-250a's are really magnificent with Maggie's!
Will sell the Krell.
If you read some of my recent threads (which are all really about this same issue), you'll see me engaging in a similar hunt (although my budget was more around 4k for an amp). So far I've heard the following on my 2.4s:
Classe CAP-151 (leftover from before the upgrade)
Pass Labs XA-30.5
Pass Labs X-250.5
I'm still in the middle of comparing the two Pass amps, but so far my favorite has been the XA-30.5. It runs out of steam a bit on bass, but I've addressed that by adding a subwoofer. It may be the lowest powered of the bunch, but it has the best imaging, soundstaging, and the most natural vocals of the bunch. Although others (including the previous owners of my 2.4s) have loved the Mac, I did not... and honestly don't know how anyone else could if comparing it to the Pass models. It obscured details in the music and added grain and harshness.
Audiojan...if you went with a Class A Krell, I think the sound will not be as forward as the more modern Krell sound is, which is why I included that link above. I think Class A biased amps will give you that more liquid less edgy sound (so look for older Threshhold, Pass Labs, Krell, and even Accuphase amps biased in Class A). The main thing though is having an overbuilt power supply that can push through a lot of current given the dips below 4ohms that Unsound points out happens for much of the frequency band with the 2.4s. The Thiels are sensitive enough that you don't really need much more than 100wpc to play them loud, as long as the amp has an overspec'd power supply and can also deliver a lot of current. If the amp is not capable of pushing a lot of current, you will then have tonal aberrations, because the tough load points happen especially in the lower registers, and then the 2.4s will sound tipped up and thin.
Second day of trying out the Mark Levinson 334 and I think I've found a real gem. The slightly dark (yet detailed) sound of the ML meshes nicely with the extremely neutral Thiel's.
Best way to describe it calmness. It just sounds right.
Ok... so now I need to sell off the Krell. It has served me well.
Check into the issues with the caps on the 3xx amps. They are known to fail and require replacement. If they have not been replaced there is a good chance they may need to be and the repair is expensive through the Levinson repair services. Great amp - just be careful you don't have to put another $1,000+ into it. They are often priced low because of the cap issue. If you really want it and the repair has not been done, get an estimate for replacing the caps and see if you can find a non-Levinson place to do the repair, just in case.
I appreciate the input and the heads-up about the caps. They are fairly recently replaced though, so I should be good for many years to come.
One thing that really strikes is the depth and height this amp can re-produce. The Krell was more forward (to be expected) and extremely detailed, kind of calling attention to all the details. The ML is kind of just "there", you hear all the details, but more in appropriate "space". I used the word calm before to describe it and that's very much what it feels like listening to it.
Before the music was played in front of the speakers (and yes, the speakers disappeared) and now it's more behind the speakers (and you still can't pinpoint the sound source).
The combination of the Thiel CS2.4's and the Mark Levinson 334 is very, very special. Yes, I've heard better, but that was with the McIntosh MC1.2kW mono blocks, so many magnitudes dearer.... still the 334 is not that far behind in my room and at my volumes (larger room and louder might be a different story, but I would give you way before the amp will...)