First, if you're happy with the JC-1s, I'd stay with them.
Second, if you really must try the Pass amps, the X350.5 is supposed to be more liquid and pleasing, as well as the more current model. While the X-600s are arguably the best of the X series and really do sound great (I have a pair), it seems like you don't need the extra power.
Third, the only real way to make a determination of which of the three amps is best would be to audition them in your system. It would be real hard for me to be able to discern a difference between these three great amps without knowing how all the system synergies will work out. Is there any way you could try the Pass amps at no cost or minimal cost? (Of course, you could always buy them used then sell them for about the same price.)
For insight on the 600 vs. 350.5 debate, check out Teajay's excellent reviews of the Pass line. He has had X, X.5, and recently XA amplifiers in his system, along with Aleph and Edge.
I have heard great things here about the JC-1, but can't recall comparisons to Pass.
First, thanks to Honest1 for your kind remarks concerning my reviews of different Pass Labs gear.
Veloceracing, if you enjoy your JC-1's now, I believe you would find the 350.5 would offer another level of refinement and musicality to your system. Remember your amps give 20 watts of class A before going into A/B biasing. The 350.5 gives you the first few watts in single ended class A then goes into class A for 50 watts before it goes into A/B biasing. You will hear the difference with the speakers you drive along with your excellent upstream gear. The 350.5 I believe is a better sounding amp then the 600 monoblocks and offers great power to drive any speaker to high DB levels. The .5 series really was a qualitive improvement over the first generation X-series.
Jameswei, is quite right you have to try the amp in your own system to really tell if its for you based on system synergy and personal taste. I still assume, seeing the rest of your systems' gear, that you would love the 350.5 in your system. Let's be serious more insurance for health or for your car, when an up grade can be done for your system, are you MAD, of course you go for the amp, everthing else can wait!
I have had a passing interest in the x350.5 for a while, to drive my Wilsons, so thanks teejay for your input. I always knew this was thee place to come for comfort and guidence in prioritizing things audio, and how they interact with life's choices. Having sold my first-born I would know. (The buyer wants a refund.)
Wow! Thanks to all of you for the quick, detailed and informative responses! Let me try to answer collectively: you are probably right that because of my music and environment I will not need th sheet grunt of the X-600's. I mean, if I decide to hold a week-long salute to organ music well ... yea, maybe I might need horsepower. The JC-1s with 400WPC have had no issues whatsoever powering the Prodigys and the SoundLabs. So the X350.5 should not either.
The only reason that I was considering the X-600's was because of the dreaded crosstalk issue: there's something appealing and logical about mono amps. On the negative side, though, one less amp means once less box that makes the stereo room look like a mad scientist's laboratory.
The advice to audition the amps is reasonable but, regrettably, I don't want to take advantage of my local dealer. I can't afford the new price tags of either component. I was just attracted by the fact that the X-600's and the X-350.5 are avaiable at roughly the same price of around $6,000.
But there is one thing that rubbed me the wrong way about the responses to my question: Jameswei is on record as stating "First, if you're happy with the JC-1s, I'd stay with them." What the hell????? What sort of audio talk is this? Are we sure that Jameswei is really one of us? Can someone do a background check on him? I would not be surprise if we discover that he is a paid lacky of the International Global Book Readers Consortium. That sort of reasonable talk has NO PLACE on Audiogon.
As a refreshing comparison, Teajay rightfully advised me to forgo that checkup to find out why I'm spitting blood and whether the numbness in my arm is anything serious. "Everthing else can wait!" he says. Now THAT'S sound (get it ... "sound"?) advice!
If your JC-1s aren't yet broken in, I suggest you haven't heard them. Play music through them around the clock. Volume level doesn't matter (just not zero), nor does high or low bias setting. They will become much more agile, dynamic, sweet, and extended. I recommend giving them the time they need, as deals on other amps will come along if you decide to change.
Others have expressed the .5 versions of the Pass amps are better, although I have not heard them side by side. The X600 is not an involving sounding amplifier, in my opinion.
It may be worth noting that performance measured by Stereophile (Feb. 2003 issue) of the JC-1 showed output far in excess of ratings, I think nearly 600 watts into 8 ohms before clipping and about 1100 watts into 4 ohms.
Hello Essentialaudio: The JC-1s were purchased new on 02/05. On average they are used about 4 hours a day so they passed the 1,000 hr mark a while ago. Again, I want to be clear here: I think the JC-1 is a stellar product. I am not succeptible to the stigma some place on "low sticker" audio gear (as if $6,000 is a trifle sum). More expensive isn't always better. More expensive usually correlates with low production numbers, as far as I'm concerned. So it's not that the JC-1s are lacking in something and I am looking elsewhere for satisfaction. It's just that I want to try a Pass Labs amp. It's more of a whim issue. Thanks.
Veloceracing, at the risk of being dogmatic, I _strongly_ recommmend breaking in the amps 24/7 with music playing, not cycling the power. You've probably broken them in a good bit but perhaps not as effectively as running them around the clock (not just turned on - signal must be passing through them with speaker loads connected).
By the way, they respond well to better power cords, although the stock cords aren't too bad as stock ones go.
Without trying to be disrespectful or argumentative with or towards Essentialaudio, I have heard he's a good guy and a runs a fine salon, I have this over and over again that if someone thinks the JC-1's are lacking something that the amps are not fully broken in. Well, maybe, but it just might be that the JC-1's do lack some sonic quality that that person is looking for.
I have heard the JC-1's, never in my home system, and believe they are very good amps and a bargain at what they retail for, however, I don't think they are as good, at least to my ear's, as the the Pass Labs X-.5 series in many ways. To be as fair as I can be I never had them in my own system but heard them in other systems with similar gear that I have at home.
Finally, I'm just a crazy audiophile with no invested interest regarding which amp anybody buys, but I do like to pass on any information that might be useful to someone trying to get some feedback in their auditioning process. On the other hand, Essentialaudio is a dealer who sells the JC-1's and does have an invested interest to promote and defend this product.
Touche, Teajay. I may wax enthusiastic about the JC-1s, but that's because they work well with Sound Labs. Alas, they're not for everyone. I would sell other solid state amps for the speakers if I honestly felt they were better and/or a better value. If you happen to prefer Pass, Krell, or Levinson, so be it. Enjoy the pursuit, but most of all, enjoy your music.