Amp upgrade for Thiel CS 3.7

Hi everyone,

At the moment i am using a Classé CAP-151 int amp to drive my Thiel CS 3.7
The amp is doing ok but a much bigger amp would obviously be more appropriate to drive my Thiels.
I've seen a very nice Krell FPB 700CX  for sale at a reasonable price.
Would that be a good investment or not ? would it be overkill ?
Let me know what you guys think.


At first, I'd say overkill for the 3.7's-But if you are getting a good deal, what the heck. But Krell yes!  Thiels should have double down power. FPB 300 would do real well, and would be half the money. The 700 is in 5i territory, or 7.2. Lots of mass and lots of heat!. I had an fpb 300 with my 2.4's, which was great, but more than I needed. But at the price, I could afford the extra power,  I'm  going to use a pair of fpb 250 monos for CS 6's, which should be ideal. I've had 2.2, 2.3's 2.4's, cs5i's, and finally CS6's. Would really love a pair of 3.7's!

The Theil's need an amp with current, solid state that can "almost" keep doubling it's wattage to 2ohms
This means a solid state amp that uses BJT (bi-polar) output transistors, Tube, Mosfet, and Class D need not apply. See impedance v -phase angle graph.

Quote from Stereophile's measurements
The sensitivity is usefully higher than average, which is a good thing considering that the CS3.7's impedance remains between 2 and 3 ohms over much of the audioband (fig.1), and that there is a demanding combination of 3.8 ohms and –40° capacitive phase angle at 60Hz. Thiel specifies the impedance being nominally 4 ohms, with a minimum of 2.8 ohms. I actually found the minimum impedance to be 2.4 ohms at 125Hz.
The difference between 2.8 and 2.4 ohms is academic, either mandating use of an amplifier that has no problem delivering high currents.

Cheers George

The CS 3.7 is a very fine loudspeaker from Thiel.
Not only does it require a large listening space (20x20, 25x25...)
it craves a high -current power amp to boot.  Choose wisely and you will be sonically rewarded.

As of recent, I keep seeing Classe' integrated amps pop up for various speakers. It must be pretty good to excellent in receiving the coverage.

I have auditioned the CS 3.7 w/ an Anthem 225 integrated and there was plenty of power and current to rock this speaker. Just another brand to consider.

Happy Listening!
2nd Note;
both B.A.T. and Pass Labs integrated amps are on my must demo-list as well.
Thanks guys for your input.
I also think the Krell 700 is overkill, very big and runs very hot!
I've red that many CS 3.7 owners found that the best amps for this particular speaker are the Conrad Johnson Premier 350SA or the McCormack DNA-500.
Both of these amps are difficult to find used...

michaeljbrown, how do you like your CS 6's ? i was thinking of purchasing a pair since prices are pretty low used.
Before that i need a bigger amp.

jafant, what thiel speakers do you have, i remember we spoke together on the forum last year i think.

Cheers Thieliste

One other thing, at the end of the month i will have the opportunity to listen to the new Mark Levinson line up : the n° 526 preamp, the n° 536 monoblocks and the n° 519 audio player.
I'll let you know what i think.
Krell has always made well respected products, yet...
Please do not be offended: I find the Krell to be somewhat lacking in imaging, AND, to me, sounds a bit grainy in the upper midrange. I would not choose it, but that's me. You do need a stable amp that keeps doubling, as pointed out by georgelofi.
The THIEL's are ruthless in revealing products upstream. I'd prefer a Classe Amp, or a used Gryphon, (though probably out of the question financially.)
Good Listening.

Ironically, Thielist, I have not yet heard my CS6's. They were damaged in shipment due to inept packing by Craters and Freighters of Cleveland,which I do not recommend. I have repaired the dent, sort of, but now await the arrival of the Krell 250 monos. I will let you know how these match up. However, my experience with Krell has been excellent; the fpb 300 dominated my thiel 2.4's--by that I mean the speakers opened up dramatically, without the analytic "bright" sound attributed to the Thiels by listeners who had their speakers underpowered or paired with inferior electronics. Krell eptiomizes high current amplification, and has an outstanding service department. I have high Regard for Classe as well; my humongous CAT 660 was humiliated by a pair of 300 wpc Classe monos in an A-B test conducted by my friend and Classe/B&W dealer in Lubbock. 
I have heard the grainy/imaging complaint as voiced by Larry; however, I have not observed that with the 2.4's. I don't claim to have golden ears, not at my age, but I will share my experience with the CS6's.
Cheers, as they say up north!

Good to see you- thieliste

the Krell would be ideal- do not worry about overkill.

I own the CS 2.4SE loudspeakers from Thiel. I, too, am shopping around to complete my reference system.

keep me posted on the Mark levinson demo.
I would love to hear the No. 585 integrated w/ the No. 512 cd/sacd spinnner.

This brand would be a sonic match for Thiel loudspeakers, as well as, Classe'.

I'm sorry for what happened to you CS6 that's a shame!
Hope you will get them fixed properly.
Looking forward to your experience on your CS6.
I've seen a very nice pair for under 3000 $.


Really happy for you that you were able to grab a pair of CS 2.4SE.
These are beautiful and rare one the used market.
Wish you luck on completing your reference system.
The Mark Levinson n° 585 is actually a verry good match for the CS 3.7, i know someone who has that combo.
I just ordered the n° 519 network player to replace his Aurender.

I'm not going to buy that Krell 700cx, it hasen't been recapted the owner told me.

I've been speaking to Steve McCormack lately and he sumitted me the idea of his latest reference system SMC Audio as an option for me.
Looks like he's making some very nice gear with his new company.
I'm considering this option seriously.


Hi Thieliste,

I recommend that you seriously consider a Classe’ DR-9 (or two). You should be able to find a nice one for around $1k. Have the seller send it to Classe’ to install a refurb kit (new power transistors and critical caps). I have one that has this "upgrade" and it sounds ridiculously good with my 5i’s. None of the dark sound of my DR-25 and has much more energy than my other "stock" DR-9. Very open, dynamic, tonally rich, and slams in the bass. Excellent imaging and a BIG soundstage. I much prefer its sound to my Krell FPB-600c with my 5i’s. None of the grain and slightly over-prominent upper-mids and treble of the Krell that is problematic with the Thiels.

Just make sure to use it (and all early Classe’ amps) with the single-ended (RCA) inputs as the XLR inputs use an op-amp in the circuit and sound much less open and dynamic as a result.

Best to you Thieliste,
I've gone through most amps available on the market in the past few years and i came to the conclusion that the best one of them all for Thiel CS 3.7s is the Gryphon Diablo 300 by a wide margin.For any future Thiel CS 3.7 owner i've done the job for you, just get a Diablo 300 and don't look back.
^Just because it might suit you, doesn’t mean it’s necessarily the best choice for all. Some with particularly large rooms, might be better off with more powerful amplification commensurate with the CS 3.7’s power capabilities, and depending on sources might find some of the other capabilities of the Diablo superfluous.
^” No you don’t need more power...”for a larger room?
You might not, but somebody else might.
3.7s are not made for very large rooms, you loose all the bass.People with very large rooms will look at more suitable speakers for this size room.

^Jim Thiel recommended the Thiel CS 3.7’s for an amplifiers up to 600 Watts, and used an amplifier rated at 600 Watts during their development. Why?
 With the appropriate amplification, and especially when coupled with Thiel's own subwoofers; the CS 3.7's can comfortably fill a rather large sized room.
Thiel CS3.7 loudspeaker Specifications |
By today's standards it is much better to choose a used Diablo 300 vs an old Krell 600, unless you absolutely need separates.Quality vs quantity.
^That is your subjective opinion. Not all would agree. While it's impossible to know for sure, I'll hazard a guess that Jim Thiel would have  stuck with his Krell power amp over the Gryphon integrated. Once again, it depends on the circumstances. One might be better than the other for some, and the other might be better than the other for some others. New is not necessarily better than old. There is also a price discrepancy that can't be ignored. 
There is no way old Krell design could compete with todays Gryphon gear in terms of sound quality.Gryphon was most likely not available in the US when Jim was still alive.At the time it was either Krell or Bryston you didn't have much choice for Thiel speakers.

Jim would have been blown away if the Antileon Evo existed at the time he was designing the 3.7s.
^There were others, and better than the Bryston’s too. Gryphon had a inconsistent presence in the US for a while, but I'm confident Jim knew what was going on globally. For the reasons mentioned above, I think Jim Thiel would have chosen the big Krell over the Antileon Evo(s) for the development of the Thiel 3.7’s.