Many different types of tube amps are available, many audiophile like single ended amps. These are most commonly lower powered amps 8-20 watts, these amps can really work well with efficeint speakers and bring wonderful midrange as well as low level information to light. Push pull designs will typically have more power and work well with less efficient speakers, but do not always have the detail of small set amps. I personally have a push pull design amp, I purchased it because it can drive most speakers. types of amps to consider would be Set, OTL, push pull designs as well as others. I own a Atma sphere amp, it is a OTL design, to me this amp sounds very neutral and gives a great sound stage, this amp works best with efficient speakers 8 ohms or greater. Possibly you can just borrow someone's amp who lives near you this would surely be the least expensive AB comparison.
Don't do it All Tube Pre amps will pass DC to safely use a tube pre you must engage some internal caps. As far as Krell amps being edgy or bright my findings are just the opposite. I am on my 3rd. Krell. How about getting rid of the pre completely. try using a cd player with a volume control I am running my Wadia 861 direct and could not be happier.
I had a Krell KAV250---traded it for a Krell 200C and thought it was fantastic untill I auditioned a Music Reference RM-200. I wasted no time and sold my krell 200C and my KRC-3 and purchased the Music Reference RM-200 and a BAT VK50SE. I have purchased other tube amps since then, but they have all been tube amps(still own the RM-200). IMHO once you go tubes there is no looking back. The sound is warm and very, very real. Tubes pull out the emotion in the music that I am not sure any solid state piece ever could. Sure you have to let them warm up---you may have to adjust them every once and awhile,and some give off major heat( which can be good in the winter) but I think you will find all that well worth your while in the type of music reproduction you get back! And then we go back to the issue of what other components are in the system. It's like a work in progress--untill you get all the right pieces it may not be perfect. But thats why we are here hanging out on Audiogon instead of doing something else! Just one persons take on the matter---Good luck and enjoy the ride!
If *you* are happy with the Krell, then I would not worry about what others say. Furthermore, I have noticed many posts on Krell gear in general, at various forums, criticizing the products as edgy and bright. Indeed, that may have been the case with the early Krell gear of 10-20 years ago. However, in my experience, that is simply not true of the current line. If anything, I would say the treble in their current KAV line is slightly shelved down. Among published audio reviews, you will likely notice that Krell gear is labeled as dark, not bright!
Nevertheless, there is something about the Krell sound that some listeners dislike. I can understand that perspective. Simply calling Krell bright, harsh, edgy, or any of the other critiques leveled at the worst aspects of solid-state gear is, however, inaccurate. I do not think it reflects an honest evaluation of the Krell products, or, at least, an honest attempt at explaining what these listeners disliked about the product.
I have limited experience with tube gear, but I like what I've heard from BAT. In fact, I would argue that their new VK-300X integrated with super-tube option shares sonic similarities with Krell's current KAV-300iL integrated. Both products are ever-so-slightly dark.
Good luck with the hunt if you find that you must keep looking.
Tbe amps. I went to the local McIntosh dealer interested in getting the latest 6-channel (solid state) amp. I noticed the new 2102 tube amp and asked to hear it, after having listened for quite some time to the solid state. The guy went behind the wall to change cables and, after the 2102 warmed up, he let me hear it. A accused him of changing speakers on me as it sounded so wonderful. I had to have him reverse the experiment while I watched to convince me. If you can hear the differance between solid state and tube, you will be hooked forever! I now own a 2102 and my wife noticed right away how it sounds 'woodier'.
I use the FPB300 to drive the top end of my B&W's, and as others have said -- not too bright compared to live music.
I use Krells own KRC-HR preamp.
Also, if you really want your FPB to sing, add the Pure Note Sigma power cord; a match made in heaven!
By the way, if you try a tube preamp, make sure you make the internal adjustments first, or you my fry some of the transitors, etc.
A Krell FPB-300 used to drive my Aerial 10Ts. From my perspective, it was NOT edgy and is a bright. I agree with the comments above: my findings are just the opposite as well. If anything, the FPB-300 is just sligthly on the warm side of neutral.
It wasn't until I replaced the Krell that I discovered its flaws. Compared to my Spectral DMA-150 Mk2, the the FPB-300 suffers a bit of grain in the midrange. Also, it's a bit slow, particularly in the bass (but then most amps are compared to Spectral).
If you hear bright and edgy then I think you need to address something else in your system, not your Krell.
There is no simple answer, but I would be highly suspect of simple statements that Krell amps are "bright" or edgy.
I have owned both the KAV-500i integrated and the FPB-600c. I found both of these amps to be spectacular sounding with my B&W Nautilus 801 speakers. I have now decided to biamp with tubes on the mids/uppers (mostly because the 801s let you biamp and I fell in love with the new VAC Phi 70s). I've concluded the following:
1. Boy, is the Nautilus 801 a great speaker. (But by all means take the grills off the mid and woofer).
2. The VAC sounds extremely fine up top, but truth be told, I am hard pressed to distinguish its sound from the Krell on the highs. That's right -- I am saying that the Krells do about as well on the highs as a push/pull triode 300B valve amplifier. In the crucial upper midrange, I would say that the two are extremely similar, except I find the VAC to be noticeably more forward than the Krell FPB-600c, although to be honest I can't tell you which one is more "right."
3. There is something emotional about tubes, but who can say what it is? As great as an FPB-600c is, it is hard to really love it -- it's a big, heavy, metal beast that sits there looking cold, impassive, monolithic and indestructible. It has seemingly limitless headroom and just makes everything about the music seem so effortless (until it blows your house fuses). On the other hand, the VAC Phi 70 is this gleaming retro object with evocative backlit meters and big, delicate tubes glowing serenely behind an etched glass casing.... If audiophiles were honest and admitted there is more to the audio experience than just the sound, perhaps we'd understand the romance of tubes a bit better! Maybe you should make your decision on which sci fi aesthetic you like better: if you're an HR Giger person, get Krell; if you like Jules Verne, get tubes! :o)
But from a sonic point of view? I don't see -- er, hear it.
4. Krells slow on the bass? Not the Krell's I've owned. Fast, authoritative and totally in control -- that's the experience I've had with these Krells. I don't know of any amp that does bass nearly as well, including Pass Labs and Levinson gear I've heard extensively.
I run a Krell 400cx into Thiel CS6. This is NOT a harsh system. Do not be taken in by tube "mythology." That Krell you own is wonderful piece of equipment and is state of the art. Patekswiss said it all: fast, authoritative and in control.
You won't get that with tubes, can't be done. They can't push the current with the same linearity.