B&W says 50 wpc minimum, the amp is 25 wpc. So, I rather doubt it will play anything but softly before clipping.
Though I know Pass has a rugged build, why push it?
Though I know Pass has a rugged build, why push it?
While the XA25 is rated at 25 watts into 8 ohms and 50 watts into 4 ohms, John Atkinson's measurements that were reported in Stereophile indicated that it is capable of providing 80 and 130 watts into those impedances, respectively. A lot of that disparity is apparently due to the Pass specs being based on distortion percentages that are extremely tight and are much lower than the ones JA bases his results on, and presumably some of that difference reflects the amp's capability after entering class AB mode rather than class A.
The speakers are rated at 89 db/2.83 volts/1 meter, with impedances of 8 ohms nominal and 3 ohms minimum.
FWIW, my XA25 has no trouble cleanly generating 105 db peaks at my 12 foot listening distance, with 6 ohm speakers rated at 97.5 db/1 watt/1 meter. However 89 db speakers will require approximately seven times as much power as 97.5 db speakers to generate a given volume.
My guess as to the bottom line is that the answer will depend on the dynamic range of the recordings you listen to, with classical symphonic recordings that have been engineered with minimal or no dynamic compression being among the most challenging kinds of recordings in that respect, as well as your preferred listening volume, room size, and listening distance.
The XA25 is a better amp though. Class A amps are rated according to their bias points, and in push-pull configuration, the class A envelope is double the bias. In this case, 50 watts. Beyond that you're into class AB operation. That's where the XA25, and push-pull class A amps in general, get their healthy headroom.
I'm about 8 ft. from the speakers. Probably about 15 ft wide for the listening area. Although, the room is completely open behind my listening position. Approximately, 32 ft total in length from behind the speakers to the end of my kitchen, a total open floor plan.. I know pass is a better amp, that's why I am hoping for it to work. I don't listen to any classical, but I listen to everything else. I want to listen to classical though because I love music. I am CD only using a roksan k3, emotiva xsp 1 gen 2 pre and an emotiva xpa 2 gen 1 amp. Emotiva is leftover from my more entry level system. It sufficed before getting 804s, except for the xsp 1 gen2 which replaced an emotiva USP 1. The xsp 1 is nice for $1200.it can replaced later. I need a solid amp. I am strictly 2 channel. $5000 is my absolute limit. I appreciate all the advice I can get. Still on the fence. Maybe the pass labs will work? Any other recommendations?
I'm using a First Watt F5 clone biased to 31 watts with a pair of Focal 936's (90dB sensitive). It in no way lacks the power to drive those speakers to any volume I please. The F5 and XA25 are similar, but there are important differences. The F5 is a 2 stage amp and the XA25 is a 3 stage amp. The XA25 has a meatier, higher voltage power supply, kinda like my build. It uses the exact same input JFETs as the F5. It uses current feedback instead of voltage feedback, like the F5. The real difference is in the massive output MOSFETs which don't use any kind of degenerative feedback, unlike the F5. That's an amp that will legitimately double it's power into half the impedance. The other notable difference is in the cascoded MOSFET gain stage that drives those massive output devices. If they're the ones I'm thinking of, they're kinda tough to drive with K170/J74 JFETs so the intermediate stage is required. The F5 is a very nice amp with a muscular, detailed, holographic sound. The XA25 is like the F5 built with a "cost is no obstacle" mentality. It does everything the F5 does, but better in every way.
As I said, I know Pass overbuilds his amps, and you might not have any issues, but once again, why tempt fate?
If it were me, I'd take the safe route and get a higher powered amp. I believe in having lots of headroom when it comes to power.
Then if you decide to change speakers,you'll have a wider range to choose from.
I see some XA-30's for sale that are under $5K, still low, but closer to recommended specs. There are a pair of XA-100's, asking $6.5K though, but would be a real killer.
There are other manufacturers, but I don't know if Pass is the only one you'll consider.
You have gotten some good responses and comments. I’m inclined to agree with those who have raised the very important consideration of ’sound quality ’ as compared to increased quantity (higher oower/more watts). The Pass Labs XA 25 is capable of 50 watts of pure class A into a 4 ohm load (this isn’t an insignificant amount). It can provide class AB 200 watts maximum into a 2 ohm load (This is impressive).
The John Curl designed Parasound A21 offers class AB 250 watts into 8 ohms and 400 watts into 4 ohms. So clearly higher power. I suspect it has pretty decent sound quality. Keep in my its DF (Damping factor) is >1100!! This suggests very heavy use of NFB. Some very respected amplifier builders such as Atmaspere and Roger Modjeski consider this amount of DF gratuitous and without meaningful benefit. On the other hand some builders (John Curl I’m sure) would beg to differ. My gut feeling is that the Pass XA 25 could very well be the superior sounding amplifier.
Is there the interest/desire to home audition these amplifiers and actually hear them driving your B&W speakers? I would bet that the vast majority of your listening the XAX25 would remain in class A operation. This is a good thing IMHO. I'm expressing my own biases. I don't believe in the cliche of "the more power the better" once you have sufficient power the objective should be placed on quality.
I consider that kind of damping factor pretty ludicrous too. 500 is pretty typical for Pass's mainstream amps, and the XA25 certainly accomplishes that in no small part to lacking any kind of degeneration on the output transistors.
If the XA25 isn't going to make the power you need, the XA 30.8 isn't either. But that's not why you should choose between them. They're totally different amps. The XA25 is a conventional push-pull topology with negative current feedback. The XA 30.8 is a balanced topology using Super Symmetry feedback. They work and sound totally different.
I just crunched the numbers for those speakers. 25 watts will yield 101.2dB at 8 feet. That is insanely loud. Nobody listens at that kind of average volume. And 25 watts is just half of it's class A envelope. I crunched the numbers on the amp, too. It seems to be running 24V rails and hits 1% distortion into 8 ohm at about 22.8V. It's current limited to 10 amp, but you'll never see that with those speakers. At their 3 ohm low point that amp will drive 173 watts into them with current to spare. That's like 104dB at 8 feet. If you typically listen at an average volume of 92dB, which is still pretty loud, you only need THREE watts with those speakers at 8 feet.
I agree with your calculations and reasoning. This is the point I was attempting to illustrate in my prior post. You can’t look at the XA 25 and conclude, "oh, it’s just a 25 watt amplifier " . There’s considerably more going on here if one can appreciate the design/circuit and implementation. As you calculated, at very reasonable (even generous) volume levels these speakers aren’t demanding much power/ watts at all. And as a reminder, 200 watts/10 amps (current max) into a 2 ohm load.
DF of 500 is still pretty high relatively speaking in regard to the XA 25. I agree the XA 25 and XA 30.8 are notably different circuit designs. I’ll empathize again, Parasound A 21 or one of the Pass Labs amplifiers, you have to hear them with the specific speaker of interest. Each amplifier will have its own sonic signature with a given speaker.
One point to consider regarding DF is it is inversely proportional to the output impedance (isn’t necessarily a bad thing) and the higher the DF the more NFB utilized (Which ’could’’ introduce some undesired sonic consequences of its own). Another point, speaker sensitivity measurements are of a single speaker. Generally 3 db is added when discussing a "pair" of speakers.
Nelson Pass makes himself extremely accessible. That's why I decided to build one of his amps. Between all the articles he's written, his Burning Amp lectures, and the wealth of information out at DIYaudio in the Pass section, there's a lot of information. He's put enough information out there to clone a Super Symmetry circuit, and some have. He generally doesn't care about that kind of stuff so long as somebody isn't building it for profit. I've never heard the XA25, but it's architecture is similar to my F5, and I've read comparisons between the two to know that the XA25 is a better, more refined version of an F5. Then again, my F5 is more powerful
Thanks for your very informative posts, Kosst. I’ve learned some things from them about my own XA25 that I didn’t know previously.
Regarding the references in one of your posts to "average volume," others should keep in mind that what matters with respect to an amp’s maximum power capability is of course the maximum volume levels that are reached on the recordings that are listened to, not the average level. And the relation between the maximum and average volume levels will vary dramatically among different recordings, depending on both the music and on how much dynamic compression has been applied in their engineering.
For example, some classical orchestral recordings that have been engineered with minimal or no dynamic compression may reach brief dynamic peaks that are 30 db or more greater than the average level of the recording. Which in turn means that around 1,000 times as much power will be required to reproduce those brief peaks compared with the amount of power required to reproduce the average level of the recording. While many and perhaps the majority of pop and rock recordings are compressed to a dynamic range of less than 10 db, which will require less than 10 times as much power for peaks than for the average level.
Thanks again. Best regards,
Quite true about the maximum power demands. Personally, I try to avoid 110dB+ kinds of volume. I just don't find transients with that kind of punch to be pleasurable. Sitting through the 45 minute orchestral presentation at my daughter's school leaves me wishing for ear plugs and counting the minutes and it's just not something I want to reproduce.
@Cal3713, I’ve sold the VAC Renaissance 70/70 MkIII amplifier and I’m using the XA25 exclusively. I decided to purchase the XA25 a few months ago while the VAC was back at the factory for a minor repair, motivated mainly by all of the glowing reviews I’ve seen of the XA25. While also taking into account the sterling reputations of Pass Labs and the dealer from whom I purchased the amp (Reno HiFi) for customer service and support, as well as Pass Labs’ reputation for building products that tend to be reliable and trouble-free over the long-term. Regarding the reviews, I found Teajay’s (Terry London’s) review to be especially accurate in its characterization of the amp’s sonics, at least with my easy to drive Daedalus Ulysses speakers.
Following are some comments about the XA25 that I had occasion to post a few months ago in a thread that was mainly on a different subject:
It comes amazingly close to the VAC with respect to dimensionality, imaging, liquidity, and other traditional fortes of high quality tube amps. It’s a bit less rich sounding than the VAC, but I interpret that as an increase in accuracy, which is fine as far as I am concerned.
On another note, happy holidays to you and yours, and all best wishes for 2019!
@almarg Thanks al. Always happy to see one of your posts in a thread, and glad you're enjoying the pass.
5 years ago I had an xa30.5 that I loved and have considered using the new model on my coincident PREs (in liu of the 300b Frankenstein's). I'll have to keep eye out for a used one to try. It's been tough to beat those amps (so far I've tried lyngdorf and atma-sphere) Dealing with pass is also leagues better than my coincident experiences.
Happy holidays to you too.
@cal3713 I also own a Pass Labs XA25 amp, which I received a few weeks ago, and like you, I also own a pair of the wonderful Coincident Frank mkIIs, which I've had for while now. Being a tube guy, especially SET, I have not been able to live with any SS amps I've heard in the last few years, that is, until I got the XA25. Teajay did nail it with his review of the XA25, and so did the other reviewers. This is an amp that is voiced with the midrange first, which is also my preference, but nothing is missing from either extremes. If you can't get the midrange right, forget everything else. Both amps have a wonderfully holographic soundstage (the Franks may have a slightly deeper soundstage), natural sounding midrange (voices are intoxicating with either), good instrument tonality and timbre. The XA25 has, as it should, better slam / impact with a deeper, more controlled bass.
Anyways, my personal assessment of the XA25 is that it is the equal of the Franks, though it doesn't sound like SET, it's neither better nor worse, just a bit of a different flavor, very easy to live with, and IMO, certainly a "keeper". I get the emotional connection to my music with either amp, so bottom line, I love them both!
The X250 isn’t even a class A amp. It’s a high bias class AB amp with a single ended bias of 20 watts.
Contrast that with the XA25 with it’s 50 watt class A envelope. That’s a plenty of amp for most people.
Macguy said his meter indicates the amplifier remains in "class A operation". So the first 20 watts of the x250 is bias in class A (bias set at 0.8 for this model per the Nelson Pass article). At his listening levels the Vandersteen speakers aren’t demanding of more than these first 20 watts. I suspect that very often not more than a few watts are utilized at easonable listening levels.
Exactly. That's my point. Folks really don't seem to have a grip on the scale of power they're really using, then go buy massive triple digit amps because they heard somebody talking about "headroom". As one reviewer of the F5 put it, if you're speakers need more power than the F5 puts out, they're just poorly designed speakers.
I do understand the desire/concern of many listeners in regard to "headroom" availability for demanding musical peaks and the fear of having insufficient ’juice ’ on hand. This is a common topic in audio forums. I do think that to some extend it gets blown out of proportion. I do not agree with the popular audiophile axioms, "the more power the better" or "enough power is never enough".
I’ve read (more than a few) testimonials on various forums from those who drive their 100 db> horn speakers with 200- 300 watt amplifiers so that they "never run out of headroom" regardless of volume or music genre demands. So without any doubt there are those who have different perspectives and experiences. Speakers of this type can provide reasonable SPLs (65- 75 db C weighted) with only 1/20- 1/100 (0.05 to 0.01) of 1 watt
A minor point but one that should probably be mentioned is that the Vandersteen 5 has a built-in amplifier handling the deep bass. And it is designed to be used with a passive high pass filter inserted between the preamp and the power amp, which rolls off low frequencies by 3 db at 100 Hz and at 6 db/octave below that frequency. (The built-in sub amp provides a complementary frequency response which restores overall flatness). So the power that is demanded of Macguy’s X250 is significantly reduced relative to what be required if it were driving a comparably efficient speaker full range.
In any event, it appears that the Vandersteen 5, like the currently produced 5a Carbon, is rated at 87 db/2.83 volts/1 meter, but apparently has an 8 ohm nominal impedance rather than the 5a Carbon’s 6 ohms. Assuming those specs are accurate it can be calculated that at a typical listening distance of say 10 feet, and in a medium sized room, two such speakers will produce an SPL for a centered listener that is in the vicinity of 95 db when both are driven with 20 watts. Enough for many listeners on most or all of their recordings, but certainly not enough for some listeners, especially on recordings having wide dynamic range.
I do not agree with the popular audiophile axioms, "the more power the better" or "enough power is never enough".I disagree with those axioms as well, Charles. A point that seems to often be overlooked by proponents of those axioms is that for a given level of amplifier quality more watts usually = more $, at least within a given amplifier topology and a given class of operation (A, AB, D, etc.). So if a given amount of money is to be invested in an amplifier of a given topology and class of operation, choosing an amp that has more power capability than necessary may very well mean that more of those dollars than necessary will be directed toward watts rather than toward quality. At least that’s how I see it.
I own a Pass XA-25. When I bought it I owned a new CJ ART150 stereo tube amp and a CJ Premiere 12 monoblock set up. I’ve had the legendary CJ Premier 350 solid state amp. I drive Wilson Audio SOPHIA II’s. I got here with an XA25 after exchanging email with Nelson Pass when I was thinking of a First Watt to try out. He re-directed me to take a look at the XA25. That was in November 2018. I have sold the ART 150 and other amps. Compact and commanding. I read the STEREOPHILE review and the technical assessment. All I can tell you is the little amp commands the Wilsons with authority. My sound has never been better. It paired extremely well with CJ single ended pre amps such as the ET-5 and Premier 16LS2. I tried a Pass Labs XP-10 which was a very good pre, but traded it for the XP-20. This little amp can and does command with authority. The reviews of the sound are dead on. I also use a ELAN Z cooling fan as well; it of course runs hot so the fan helps.