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24.101.215.126
I have a Pass Labs X 250.5 power amp. I am considering switching to the XA25. Pass claims the X 250.5 operates in class A mode for the first 20-25 or so watts. The XA 25 is an all-class A amp.
Do you think the XA 25 would give me better sound or is this just a sideways change??
Many thanks!
Follow Ups:
I have not had the pleasure of listening to Pass Labs in my home but I have heard them in several other setups driving QUADs. David Chesky uses the XA160.8 mono amps and it is as good a sound as I have heard anywhere.
I am big proponent of power. Large amps give a grip and control that smaller amps cannot deliver. IME. I am using the ARC REF80 which is a 75 watt tube amp. I also have(had) its bigger brother the 160S. Same circuit topology just twice the power of the 80. No question which one sounds better to my ears. The 160S delivers more grip, control, slam versus the 80. It is a bigger more robust sound.
As lovely as the small Pass amp might be for me it would never work there is just not enough power. I am a QUAD user that likes to drive them loud at times, 100dB+ peaks. 25 watts would be hard clipping.
In the end this really comes down to personal preferences, taste and of course budget. Herb Reichert reviewed the XA25 driving the QUAD 57 for Stereophile Vol. 41 No. 2, February 2018. His conclusion?
'The Pass Labs XA25 delivered a potent transparency the likes of which none of us had heard before. It was as if the audio system had disappeared, making possible a direct view of the what the microphones registered, unmitigated.'
That is very high praise for any power amp.
Thanks, Kent...helpful as always.
One respondent asked an important question--What is it about the current amp that you are dissatisfied with? In truth...nothing. I have no complaints about the X-250.5. It is, by far, the best-sounding ss amp I have heard--and I tried a few when driving my B&W Matrix 801 Series II speakers.
The idea of a smaller chassis and weight amp that I might be able to pick up by myself if needed has a certain appeal, but if it isn't a significant improvement sonically, it's not a good idea to make a change.
Perhaps there is a bit of that persistent itch to try something else at work here too.
I found tube amps just don't deliver the bass punch and clarity of a ss amp. Your current ARC amp is way out of my price range, but I'll bet it sounds fantastic!
Cheers!
You might consider a Berning ZH 270. I have been using this for years with Quad 57's. Lightweight and puts out 70 watts per channel. Very easy on tubes also. Mike
Sounds like class D is actually an option for you.
'One respondent asked an important question--What is it about the current amp that you are dissatisfied with? In truth...nothing. I have no complaints about the X-250.5. It is, by far, the best-sounding ss amp I have heard--and I tried a few when driving my B&W Matrix 801 Series II speakers.'
My advise to any audiophile if you are happy with the sound DO NOT listen to other stuff. You will inevitably find something else you prefer and then be disappointed with the current setup. And it will probably be way more expensive and then......
'Perhaps there is a bit of that persistent itch to try something else at work here too.'
Of course we are audiophiles we cannot help ourselves. It is the nature of the disease. I was/am perfectly happy with my ARC REF75SE but I am an audiophile and a huge fan of ARC. I had to try the latest amps and......
'The idea of a smaller chassis and weight amp that I might be able to pick up by myself if needed has a certain appeal'
Yep the reason I went with the REF80 versus the 160S. 62 pounds versus 105 pounds and a smaller chassis. Man I loved the 160S but too big, too heavy and more tubes that I want to deal with. I miss that amp.
B&W 801, QUAD ESL-63? The XA25 is just not going to be enough power for me. 40+ years ago I I worked at a B&W dealer and we also sold Mark Levinson. The ML-2 pure class A 25 watter was certainly a honey but I much preferred the ML-3 200 watt class AB on the B&W 801 (original version).
Easy-to-drive speakers are the answer. I don't want to mess around with a ugly monster amp.
Just as smooth as the best tube amps in the mids and highs, plenty of detail with no heat as a nice side benefit.
you didn't mention what I consider an important consideration: your music preferences. Fortunately, you provide that in your profile. Like me, you favor acoustical music What I find important to convey that flavor most convincingly is getting the midrange right and being able to define the space in which it was recorded. Think the magical 3D space of minimally miked recordings from Telarc and others.Nelson's amps have been specifically designed to drive electrostats since the 800A. It was one of few in that day that could drive the challenging load of Dayton-Wrights which happened to be my gateway drug for stats back in '76. He used to demo early Threshold models driving double pairs of them. It was for that reason I bought a Stasis in '81 to drive Acoustats. They fared quite well but did not possess the compelling midrange of contemporary tubes like the D79.
Like you and Abe, I moved to a VT-100MKII for a short time. While it was better than the Stasis in some regards, it was not a game changer. I later found that answer with my current VTL amps after hearing their big brothers in Sea Cliff driving the big Nola Grand Exoticas. They mated the seductive midrange with dynamic power and bass extension that allowed later Acoustats to really sing.
I think the Pass amp would be a sideways move. My suggestion is to audition more than one amp to find your new dance partner. SETs are likely not the best answer for stats. Powerful tubes with massive power supplies to deal with the reactive load are the way to go IMHO. You may be aware that Kent uses a current REF80 with his Quads. I had the pleasure of hearing his system when business travel led me to Kansas City. I confess to being more of a line source kind of guy using Sound Labs but had never heard Quads sound that good nor play as dynamically.
Should you follow my moniker, you'll find system listing, preferences and some pics for reference.
Good luck on your search!
Edits: 05/09/25
Knowing typical Pass Labs class A push/pull amps the XA25 is 25 watts class A into 8 ohms and then goes into class AB for higher power typically about 70 watts. When Pass calls an amp class A they only give you the honest class A rating even though it puts out more power.
You will typically be running in either amp in class A almost all the time, only going into AB rarely on very short high peaks in classical music. If the XA25 is a newer amp it may be improved circuitry and sound better. Otherwise my guess is it's a side ways move.
George,
You might also ask in the planar asylum...
I have '57s and have run them with Tubes, SS and Class D- different sound - but still Quads!
The Pass 250.5 will be fine, but I doubt you will exercise the amp much,
I would however suggest that you have the voltage limiting diodes installed so that there is NO risk of arcing (Quad specifies an amp output of under 30 volts to prevent arcing (a bit over 100 watts), but with the limiting diodes, your current amp will be fine.
as to how the quads will sound on SS amps - try it!
there have been many examples of SS driving quads to wonderful results, from ML-2s thru the later Quad brand SS amps: 303 & 404
Happy Listening
I would like to add a couple more comments. Everyone says "Quads love tubes". I had a couple of ARC VT-100 power amps (Mk 1 and Mk 3). They did sound lovely, but the Pass Labs amp has much clearer, more articulate bass, so I stayed with it.
Quad are a difficult load for power amps. The Pass Labs amp seems to handle this without problems.
I've been there too. While my ARC VT100mkII was a nice match for my smaller Thiel CS1.5 speakers a robust SS amp was better overall. I also ran the CJ Premier 11a tube amp on the smaller Thiels. The CJ was the more 'tubey' sounding amp with a more three dimensional presentation. The ARC was more dynamic and powerful sounding. When I tried a couple solid-state amps on the Theil CS1.5 speakers I found that I preferred them over the ARC. The ARC was more solid-state like but lacked the clarity of good solid-state. On the other hand the main thing the CJ had over the ARC and the solid-state amps was that nice three dimensional presentation and a bit of lushness. [And then I discovered the budget friendly AES/Cary SixPac EL34 monoblocks which were more to my liking over the CJ and the ARC. But that's another story].
But back to you question about the XA 25 vs the X250.5 on your Quads. I have no definitive answer but my gut tells me that the XA 25 might be under powered. Perhaps someone with Quad experience will chime in.
My question to you would be, what are you missing in the X250.5 that prompts you to consider the XA 25?
"Do you think the XA 25 would give me better sound or is this just a sideways change??"It could even be a backwards move but someone with Quad experience will hopefully chime in. Can you audition the XA 25 and return it if not satisfied?
I have no experience with Quads but I do have some experience with speakers that are more sensitive than yours yet sounded much better with more power.
- I ran the Class-AB Pass Labs X150.5 on my 91dB sens 6 Ohm nom Tannoy tower speakers. It was a good match and the sound quality was outstanding. I then ran the same speakers on a Pass Labs Aleph 3 which is 30-Watts of pure Class A audio. The sound was smooth and a little warm but compressed or restricted. It was lacking dynamics and it was a little rolled off in the bass and treble. The higher power Class-AB X150.5 brought my Tannoys to life with clarity while the 30-Watt Aleph 3 sounded almost muffled in comparison. Was this a power issue or just the Aleph 3 sound? I don't know but other amp swaps suggested that my Tannoys came to life with a little more power. (For example, the 200-WPC Classe CA-200 vs the 100-WPC Classe CA-100.)
Tannoy Definition D500 : Mfg recommended 30 to 175w RMS. 6 Ohm nom, 4 Ohm min, 91db/m/w sensitivity, 8" dual concentric mid driver (brass tweeter in center), 8" bass driver. Crossover type: 1st order LF, 1st order HF. These speakers sound better with more than the recommended minimum of 30-Watts.
- I wouldn't even consider running 30-Watts of Class-A power on my Thiel CS2.4 speakers. I -believe- the Quads have similar low sensitivity. In the case of my Thiels, they really need more than 100-Watts to come alive.
Thiel CS2.4 : Three-way, floorstanding loudspeaker. Drive-units (all anodized aluminum): 1" (25mm) dome tweeter coincident with 3.5" (114mm) cone midrange; 8" (204mm) cone woofer; 8.5" by 11" (230mm) passive radiator. Crossover frequencies: 800Hz, 2.5kHz. Crossover slopes: acoustic first-order, 6dB/octave. Frequency response: 36Hz-25kHz, +/- 2dB. Phase response: minimum phase, +/-5 deg. Impedance: 4 ohms nominal, 3 ohms minimum. Sensitivity: 87dB/2.83V/m. Recommended power: 100-400W. The Thiels sound better with much more than the recommended minimum of 100-Watts.
Edits: 05/08/25 05/08/25 05/08/25
You need to match the power of your amp with your speakers. Never run a high powered amp with high sensitivity speakers.
My Plinius SA-102 has a switch which can switch between class AB and class A. It sounds much better in class A mode.
Pass Labs class AB amps have very high bias. It is more like the first 20-30 watts are in class A.
"Never run a high powered amp with high sensitivity speakers."I don't necessarily agree with this. If the 'high power' amp is dead quiet there is no harm in running the high power amp with high sensitivity speakers.
But that's not the point. The OP is running low sensitivity speakers.
"My Plinius SA-102 has a switch which can switch between class AB and class A. It sounds much better in class A mode."
That could be true in YOUR SYSTEM but the OP is talking about running a 25-WPC Class-A amp vs his 250-WPC Class-AB amp into his not-so-sensitive speakers. Do you have a definitive answer to the OP's question?
Edits: 05/08/25 05/08/25
at which level they feel comfortable to drive?
I don't understand your incomplete sentence.
A white horse can run very fast. But you let him/her walk slowly. Does he/she feel comfortable?
I'm not great with parables but I hear that Jesus was.
Edits: 05/08/25
I would suggest you try a 805 SET amp on your Tannoy speakers.
I've thought of it. The 805 should be sufficiently powerful especially considering that tubes soft clip unlike under powered solid-state amps when driven hard.Just for grins I had a pair of flea power 45 monoblocks on loan driving my Tannoys. The sound was wonderfully warm, syrupy lush, and harmonically rich which can be intoxicating (for a while) but the bass was bloated and flabby. The 45 amps were probably putting out a whopping 2 or 3 watts. Sound was OK with "simple music" but quickly fell apart with more going on. I attribute this to being way under powered for my speakers.
Loaner pair of 45 SETs.
One of my Tannoys. Probably not what you were thinking.
Edits: 05/08/25 05/08/25
-to run a 45 based SET amplifier! I'm sure you know that.
SETs only have about 20-25% usable power. If you push them too hard they get flabby in the bass... They really shouldn't be exposed to bass since the inductance in the output transformer is usually too low due to the cut core. That causes the load impedance to go down quite a lot; bad load for a power tube.
A properly fixed up Dynaco ST35 (their best sounding amp) would be a much better choice for the Tannoys.
"They really shouldn't be exposed to bass since the inductance in the output transformer is usually too low due to the cut core."
I would go as far as saying that the inductance in a gapped core output transformer is "always too low". I limit the low frequencies at the input to my SE 6b4g amps at around 200Hz. This keeps the load line looking almost resistive.
When you allow low frequencies to be present in the output tubes and at the primary of the output transformer, all the music follows the "beach ball" shaped load line caused by insufficient inductance. This type of load line operates the tube in some very non-linear areas for part of the waveform.
So it is not just the low frequencies that suffer.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
-
I've used a 45-tube amp with 89 db. speakers, in a 12' by 24' room, but it handled the music down to 200 hz. A 24 db./oct, active crossover, cut the bottom end off from 200 hz. down, and a pair of active subwoofers handled the bottom 3 octaves. It sounded very good IMHO.
mg16
"but it handled the music down to 200 hz. A 24 db./oct, active crossover, cut the bottom end off from 200 hz. down"
That helps more than most people would believe.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Quite the opposite, my wife told me the 805 SET delivered the best bass in our house. I have a Cary V12. I think it depends on the design of OPT and whether it was cost reduced.
But what I said about low inductance at bass frequencies is correct.
If you prevent the amp from being exposed to them you'll find it sounds much better because it will make less distortion. The low inductance at low frequencies causes not only less bass response but also increased distortion.
By playing an amp that does not have this problem you'll see what I mean.
805 SET can output 48W per channel. My wife likes the sound of it and also the look of it.
Edits: 05/08/25 05/15/25
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