Pass Labs amps. Help me choose.

Speakers: Focal JM Labs Electra 1037BE
Room: 15 x 20 x 10 (w x d x h)
Listening Volume: typically 70 - 80 db at listening position. occasionally peaks at 90 db with symphonies (Mahler, Tchaikovsky). Rarely if ever above 100 db.

First a little background. I had an opportunity to audition X-150.5 at home, and I instantly fell in love. I have a stereo + multi channel music system, and I need five channels of amplification. I have immediately acquired X-3 for center and rears, and have been looking to get X-150.5 or X-250.5. In the mean times I was using X-3 for fronts and center duties. I had B&W Nautilus 804 speakers back then.

Fast forward a few months, I have replaced B&W with Focal Electra 1037BE. Focals are wonderful speakers, but it turned out they are a mismatch for X-3. When driven with X-3 the tonal balance is noticeably lean. X-3 couldn't control the bass and dynamics, and loud transient became muddy. Not a big deal, as my intention was to use X-3 for center and rear anyways, but I still needed amplification for the fronts. I've then acquired Levinson No 335 to drive Focals. With Levinson the bass control and dynamics are back.

Objectively, No 335 is an excellent amp and I could happily live with it for a while. However I am still partial to Pass Labs, and I would like to get a proper Pass amp for my speakers and compare against my Levinson. I do miss the musicality and the ease of flow with the previous set up with Pass amp. The amps I'm currently considering are the following:


X-350.5 and XA-100 are within my budget. XA-100.5 is a somewhat more than I would be willing to spend on amps. But if it comes down to only XA-100.5, then I am willing to take a leap.

Obviously my primary concern is whether the amp can drive my 1037BE. They are not an easy load where the impedance swings from 3 ohm in low bass to 18 ohm in upper midrange. X-3, a sibling of X-150, had problems driving my speakers. Personally I would choose XA-100 if it doesn't show the problem X-3 did and can drive my speakers with correct tonal balance. I don't know if it can or can't. X-350.5 looks great too. Two concerns with X-350.5 is that I don't want to pay for the powers that I may never need (350W @ 8 Ohm and 700W @ 4 Ohm is really a lot of power), and I may later regret not getting the XA series and just "settle" with X series. Then XA-100.5 would probably be perfect, but with about 2x the cost.

That's where I'm at right now. If you own any of the models listed above please let me know what speakers it's driving, and how you like / dislike about your amp. Thanks,

Yes, the XA-100.5 will be perfect for your setup. The .5 amps will solve most all your speaker load/power output needs. Call Reno HI-FI.
what is the sensitivity of your speakers? if less than 87, you may want to try the 250.5 (i have them running a pair of magnepan 20.1s and it is excellent). i think it would be enough power because the sensitivity of my speakers is 85db. the 350.5 might be overkill and the xa100.5 might not be enough. i can tell you that the x250.5 is more tube-like in quality compared with the x250 i used to have. i know this throws a monkey wrench in your situation, but it is something to consider that would save money and not compromise sound. you are right about the pass sound though, it is the best in the world.
i had an e-mail exchange with a gentleman at pass labs about the xa.5 amps. and he "really" liked the xa100.5, so that would probably be something to save up for. BUT IMHO your levinson should sound (overall) as good as any of the non-XA amps you are considering- stronger in one area, weaker in another, etc. but still a great amplifier. or you could "feed" the 335 a warmer/better signal to get it to lean more in the XA direction. then again, if i can't talk you into liking what you already have, things might get very expensive. i have a pair of ML-33H's, and after ALOT of thought about upgrading a few months ago, i simply put on several different types of music, and my doubts just melted away. my brother still has his pass aleph amps (1.2's), and has the same "problem"- they simply sound fantastic, alblum after alblum. of course they're "old" and "discontinued", etc. as a final test of your present system, i humbly suggest that you put on some "emotional" music and see if you find yourself becoming deeply involved in the experience.
X250.5 may be the right choice. Unless you want to spend more and get the XA series amp.
Also, with X350.5 you do get more power overall that you may not use to the fullest, but you also get more Class A power than X250.5 provides. So that is also something to consider.
But overall I would think that X250.5 is all you need.
I recently auditioned the X350.5 against the X250.5 , and the X250.5 had more than enough power for my Wilson Audio Sophias in my relatively large room. Unless your Speakers are very difficult to power and/or your room is very large, save the money and buy the X250.5 , I wouldn't bother with the older Pass Labs X Amps, the X.5 Amps are worth the extra investment, save yourself the hassle of upgrading down the road, and buy the better Amp. now and be done with.
The sensitivity of 1037BE is 93 dB/w/m. The reason I am considering X-350.5 is not because of the total amount of power, but because of the amount of class A biased power.
You don't need the power of an X250.5 or X350.5 with the 1037 BE. The sensitivity is sufficiently high enough and the impedance is relatively flat at 8 ohms.

A pair of XA60.5 will do the job just fine.

Dealer disclaimer.
Completely agree with Bill (Audiofeil). For your stated application the XA60.5 will offer the most refined sound for the dollar. The key is the tame impedance curve at 8 ohms coupled to the high sensitivity... You get 60 wpc rms clean class A power (120 wpc peak) versus the ~20 of the 250.5 or ~40 of the x350.5. Visit the website to learn more specs. The XA.5 amps are the pinnacle of Pass Labs and will have a leg up sonically, given appropriate system match. In your medium room with those speakers the XA60.5 should be the bomb.
French fries,

I had a ML 333 for 8 years driving a pair of Thiel 3.6s. I had thought it was a good combo, but slightly veiled. For 3 years, I had thought maybe the Thiels were the weakest link in the system, and that they would be the next item for me to upgrade.

My 333 had suffered blown capacitors three times during those 8 years. Twice under my ownership, and once under the dealer's care (I bought it as a demo, and found out last year from Harmon that the dealer had sent it in for repair once for the same issue). Harmon had switched their capacitor supplier after taking over from Madrigal. And the amp sounded better with the new cap. But after the third incident, I was ready to part with ML amps. (I still do have high regards for the 33 and 33H. I think they are miles ahead of the regular 33x series)

But the 33x series is nowhere near the Pass X350.5. I was in awe when I first hooked it up to the Thiel 3.6. With the X350.5, the Thiels had bigger soundstage, deeper (and more) bass, and the midrange sparkle. It made the ML 333 sounded like veiled, flat, and uninspiring. (And the amp has not even been broken in) I had a few friends come over to listen. These guys are very familiar with Thiel 3.6s, either through listening to my and other friends', and/or they had lived with a pair of their own. Everyone was scratching their heads, as they had all thought before that I had pushed the Thiels pretty much to "its limit" with my old setup.

For a while, I had seriously thought about keeping the Thiels longer. But my upgraditis was acting up, so I traded them in for a pair of used Parsifal Encore. (After 15 years of Thiels 2.2 + 3.6) The Parsifals are easier to drive than the Thiels, and sometimes I think the X350.5 is an over kill. But it's better to have more power than not.

Thanks all for the recommendations. I was under the impression that 1037BE is not an easy load. Just how does one determine whether the speakers are an easy load or not? The impedance curve at stereophile web site looks pretty nasty to me. The average impedance may be 8 Ohms, but the impedance swings from 3 Ohms to 19 Ohms.
The impedance is frequency dependent. Which of course is music dependent. Given your favor of classical (and not pop or rap with high rms (average) energies of 30-40 hz) and the fact that we are talking about Pass amps (very stout) the recommendation still stands that the XA60.5 would be more than enough power for your application.
3 ohms is not a big deal; it's not like its the average. In fact the average is higher than 8 ohms. But they have to dial it in to an industry standard for marketing. Again, the key is (mainly) the higher than market average sensitivity and relatively benign impedance curve.

The only TRUE way to know is to buy the amps and see if you have a match in your system (acoustic space), but I would bet real money they have enough juice to satisfy your listening habits.
An impedance swing from 3 to 19 ohms is hardly benign.

An example of a benign impedance curve would be 3 to 6 ohms, or 7 to 12 ohms. A smaller range of impedances along the frequency spectrum.

In any case, the Pass Labs X-.5 (or XA-.5) series would handle the 3 to 19 ohm impedance curve without any problem because the amps are designed to double output as the speaker impedance is halved.

This is what you want in an amp that will drive speakers with large impedance curves.

93dB sensitivity means that, as Audiofeil mentions, you'd be fine with XA-60.5, especially if your room is not too large and you don't listen at levels above 100dB.

FWIW, my speakers are 93dB, have a somewhat varied impedance curve, and I use XA-60.5. Even the XA-30.5 drove the speakers well, but not as loudly as I normally listen without straining. The XA-30.5 is a very sweet amp.
anything above 2 to 3 ohms with moderate phase angle IS benign to most modern ss high end amps, especially Pass. 19, 30, 150, 500 ohms matters even less. What we are discussing is current delivery. The Pass, as you mentioned is very capable. Thiel CS3.6s OTOH are proven tough loads (large reactive phase angle combined with impedance that dips in the 2 ohm range across large swath of lower frequencies) and are not that sensitive.
I stand my by statement. The 3-19 means little in the context of 93 dB/1Wm. Believe what you want, it's a free country.
07-14-08: Dpac996
anything above 2 to 3 ohms with moderate phase angle IS benign to most modern ss high end amps.
Perhaps so. I was broadening the discussion, perhaps unnecessarily, to include tube amps, and solid state amps that don't double output as impedance is halved.

Believe what you want, it's a free country.
Dpac996 (System | Threads | Answers)

Yahoo, pardner!

These colors don't run!
Tvad: I see. In that case a really competent tube amp like VTL or some ARCs and BATs might be a good fit too. This is one of those thorny issues that, sadly is marginalized by marketing to a single value (8 ohms/4 ohm). There is a member (I think oneobgyn) who has found amazing synergy and drive with an 18 wpc LAMM tube amp into some higher end Wilson speakers. This flys in the face of conventional wisdom, but is another case illustrating that for real answers we must try something with our own equipment.

My colors ran out of gas many clicks back. I'm exhausted.
Oneobgyn uses Wilson Alexandria X-2, which have a benign impedance curve (4 ohms nominal, 3 ohms minimum) consistent with a speaker that will work well with a tube amplifier, including an 18wpc SET.
The XA.5 series is the best sounding SS I have ever heard (I have also owned a few Alephs). I drove my 89db Merlins (easy load) with the XA-30.5 - beleive me, it was plenty of power in my application, they certainly seemed conservatively rated. Completely agree with Audiofeil on his recommendation of the XA-60.5, which saves you money and fits my prejudice that lower power sounds better than hogher power versions of a given circuit IF it is enough power for your speakers - in your case 60 watts of .5 power seems like it would be a very good match.
Hi Jylee
I am driving my Harbeth Monitor 40.1 speakers at the moment with the Pass labs XA30.5 stereo amplifier.
The Pass Labs XA30.5 is a very special amplifier and sounds really good with the Harbeth speakers. I will try the Pass Labs XA60.5 next on the Harbeth 40.1 to compare.
In my room which is 10.5 meters x 7.5 meters the XA30.5 has enough head room to spare so the Pass Labs XA60.5 should really sing.