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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
XA-100
XA-100.5

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,

jlee
jylee
tvad
9,467 posts
 
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.
dpac996's avatar
dpac996
433 posts
 
Tvad
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.
tvad
9,467 posts
 
07-14-08: Dpac996
Tvad
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!
dpac996's avatar
dpac996
433 posts
 
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.
tvad
9,467 posts
 
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.
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