Pre-amp suggestions for Thiel 2.4/Pass Labs XA30.5

Unsound, not I'm not, I guess I just saw in some other threads that people had used those with Pass Amps and had success... and they were recommended in here. And, perhaps it was just made it an easier choice to be biased towards either tubes or SS. You'd personally choose a solid-state? I did see that there's a Pass X1 up for about $1900.

Cal3713...the output impedance of the Aesthetix Calypso may present a problem in the treble region given the high impedance at 20KHz (3900 ohms vs. 30Kohms input impedance for your Pass amp via balanced, < 1:10 ratio). On paper, this suggests potential attenuation (or think of it as a roll-off) in high frequencies, so this may make the overall tonal balance more shifted towards the midrange and bass. If you are set on that option, I would highly recommend trying it in your rig before purchasing if you can.

You should check the ARC LS-17 for measurements as well. If you cannot find output impedance curve, I would call ARC and ask them. Let them know what amp you have so that they can advise you on whether the LS-17 would be agood match from an impedance perspective.

Good luck.

Are you limiting your considerations to tube pres?

Thanks for all the comments folks... it's been useful, even if somewhat discursive. I've been leaning towards Aesthetix Calypso, mostly because it is fully balanced and has especially high gain, although I see that the Stereophile measurements have its output impedance ranges from 112 ohms at 1kHz to 3900 ohms at 20Hz (balanced). Perhaps that's on the edge of being a problem with the Pass' input impedance?

So far, the other contender I've been considering is the Audio Research LS-17. Most of the other suggestions got axed because they are unbalanced, higher than my price cap, or (in a couple cases) don't come with a remote.

Unfortunately I still need to sell my old system to free up funds for any purchase, so if anyone's interested in Thiel 1.6s, a Classe CAP-151, or an Exemplar Universal player... just let me know. They'll probably be posted next month, hopefully once folks have started to recover from the holidays.

Thanks again for all the input.

I have had great luck pairing the Musical Fidelity kW preamp with Nelson Pass's First Watt amps. There is one for sale used now I believe. You will be hard pressed to find a better preamp for the money. Check out the Stereophile review (and the review's measurements), and other reviews on the unit. A tank, with a massive power supply. Truly the game changer in my system.

Nothing personal, just for the record.:-)

Unsound, I stand corrected.

I had a Thiel 2.4SE which I traded up for a 3.7

I've heard it with different combinations of Pre and Power before.

For my money, I found the Bel Canto Pre3 and REF500M to be a good pairing. I found the Bel Canto

If the budget could stretch further, I'd use a tube preamp which adds lushness and some 3dimensionality. I've heard it partner well with LAMM preamps and also with my Audio Research Ref5 and now 5SE. I am not a fan of overly warm and slow music reproduction and like dynamics so these two have been a great combination for me when I use SS power amps.

Tomcy6, actually Stereophile measured 130, 195, 332 Watts into 8, 4, 2 Ohms respectively, before clipping (as defined by 1% THD). If one were to use the 2 Ohm measure and work up, it would start to look more like an 80 Watt high current Class AB amp. Since the OP speakers don't drop to 2 Ohms, I thought we could be a little more generous with a 100 Watt high current Class AB designation. All in all, still rather close to Thiel's minimum recommended power.

One more thing, the XA-30.5 has a rather low 20Kohm input impedance on its single ended inputs (30Kohm balanced) so you want to keep the output impedance of your preamp below 2 Kohms single ended and 3 Kohms balanced.

Manufacturers seem to rate output impedances as an average like speaker makers do, 8 ohm average or 4 ohm average impedance. Their speaker impedances often dip below this average though and preamp output impedances often go above the rated number. So it's best to find a review that measures output impedance of a preamp to be sure what you're getting.

The Pass is marketed as a 30 watt Class A amp. However, it outputs 150 watts into 8 ohms and 300 watts into 4 ohms in class B. So the XA-30.5 could be labelled a 150 watt into 8 ohm Class A/B amplifier with a very high Class A bias. Read the Stereophile review of this amp if you are still not sure about this. Also consider that Nelson Pass rates his amps conservatively.

I have made a couple of preamp suggestions. I think that you would want a c-j Premier LS17 Mk II or newer, if you go c-j.

Their CT preamps use the 6H30 tube which some people don't like as much as the 6922 which c-j returned to in their most recent ET line.

Some people do like the less tubey sounding 6H30 though. If you like detail the 6H30 might be for you, with the loss of some warmth.

I would just again suggest that you get a high gain preamp in order to make it easier for your system to acheive higher volume levels so that you eliminate any concerns about the XA-30.5's suitability for your speakers.

I don't take that much stock in the meters. In fact, I wish they would do away with them, and lower the prices accordingly. Keep in mind when you start to go out of Class A, and the volume demands more power, the power needs tends to increase exponentially, and rather fast too.

Ha! It is funny to see people's reactions. The amp does, for example, easily best the Classe, as it should given the quality and price difference. Also, unless I'm mistaken, simply watching the front current meter should provide a pretty good indicator of how much difficulty the 30.5 is having driving the speakers. As I've said repeatedly, I only leave class A for 5 - 10 % of my listening.

Shsohis, despite it's (confusing?) nomenclature and marketed specs, the Pass Labs XA30.5 behaves more like a very high biased 100 Watt high current Class AB amp than a 30 Watt limited Class A amp. While perhaps at minimum power needs of the Thiels, it should be adequate in a smaller room and/or with less ultimate volume requirements, and sound quite nice indeed. Others might feel the need for more power with these speakers.
Cal3713, sorry this has gone so off topic, but I hope you can understand that on some level it was bound to happen, and with the best of intentions.

There is no way your Pass can drive the Thiel. Suggest you remedy this first.

"some successful preamp pairing suggestions would still be useful."

I see your thread has splintered in many ways. I'm shocked :-).

I have the 30.5 and 100.5's and paired them with Conrad Johnson tube preamps (ART and ACT 2.2). I am very happy with the sound. Of their preamps I'd recommend at least the 16 or 17 or you may find another brand that suits you better. Good luck.

Cal3713, the XA30.5 is quite a bit different than typically rated 30 Watt amplifiers, though I think I would choose a different Pass amp, it could very well work very well for you with your Thiel CS 2.4's.

Unsound: Yeah, I've only lived with the amp and speakers for a week or so (both are new to me), so other than some initial impressions of really hearing some great stuff out of the two, I still don't know either in much detail. Perhaps in the end I'll have to decide whether to switch to the 250.5 or change speakers. I certainly was encouraged by the volume level needed to leave class A, so we'll see... And thanks for the rec.

Cal3713, went back and read the entire thread. I still don't see a direct recommendation from Nelson Pass for the XA30.5 for the Thiel CS 2.4's. The OP does seem to vastly prefer the XA30.5 to the X250.5, but with the caveat of not having to play loud in a large room. The thread also points out that the Thiel Cs 2.4's spend much of their time below 4 Ohms. Aparently others there have had similar conjecture as I had re: output Class bias.
...But enough of that. I think the a Pass pre would be just the ticket. What ever you choose, I'd suggest using a fully balanced pre.

Cal3713...I would assume a used Pass XP-10 would be a good combination with your XA30.5 (check with folks at Reno Hifi who often have good used/demo inventory and I believe they allow 30-day in-home auditions). Other options to consider:

ARC LS-17: http://www.audiogon.com/cgi-bin/cls.pl?preatube&1328708163&/Audio-Research-LS-17-Tube-Prea. very detailed/resolving but still gives you smooth/continuous flow of music with 3D presentation

CJ Classic SE: http://www.audiogon.com/cgi-bin/cls.pl?preatube&1329081914&/conrad-johnson-Classic-SE-tube. Shoudl give you the CJ golden hue but with updated modern and highly resolved sound. SE version includes Teflon caps which take a very long time to burn in (>600hrs) but should deliver on resolution and spatiality in spades. This looks like a good deal for a brand new unit with full factory warranty.

Good luck.

By the way, thanks for the folks that did offer some pre-amp suggestions...

Unsound: This doesn't really matter, and I don't know the true state of affairs because I haven't directly compared the XA30.5 to the X250.5, but if you take a look at the entire thread, you'll see that it is actually a recommendation, and that the thread owner A/Bs the two amps on his 2.4s and vastly prefers the XA30.5. And in my listening, I'm in class A about 90-95% of the time.

In any case, this thread hasn't really addressed my actual issue. Regardless of people's perceptions regarding powering the Thiels with a 30 watt amplifier, removing the Classe from the system and using my PS Audio PWD as a preamp allows me to hear significantly more detail from my source components... so some successful preamp pairing suggestions would still be useful.

Cal3713, I don't read that as Nelson Pass specifically recommending the XA30.5 over the rest of the comparably priced Pass line for the Thiel 2.4's, only as a recommendation below 20 Watts. Seems like a highly qualified recommendation for a speaker that's manufacturer recommends a minimum of 100 Watts. I will grant you that the XA30.5 does seem to behave more like a very high biased 100 Watt "double down" Class AB amp, than a 30 Watt limited pure Class A amp. Perhaps capable of 75 Watts of Class A power into 3 Ohms before sliding into another 225 Watts of Class B power into 3 Ohms? On the other hand, I'll hazard a guess that the X250.5 is probably biased in such a manner as to be able to produce about 18 Class A Watts into 3 Ohms before sliding into about 730 Class B Watts into 3 Ohms? If you have a smaller room and/or don't listen very loud, the XA30.5 could very well work very well for you.

Hi all ! If it sounds good at lower volumes and gets worse at higher volume change amps . If it doesnt sound right to you at any volume (with the preamp in the system), change the preamp. The Cary slp-03 is killer for $2500 new / $1500 used , a true gem with nos tubes .

Here's a quote from Nelson Pass from a discussion about choosing a Pass amplifier for the 2.4s...

"The XA30.5 will beat out the X250.5 for the first 20 watts or so because it has a much higher bias, and this is particularly true of low impedance loads. (I used Thiel 3.6's to voice the original Aleph 0, and they were 2 ohms across the board). I suggest you take a look at the article Leaving Class A posted at Pass Laboratories which discusses this in detail."

(from: http://www.diyaudio.com/forums/pass-labs/175913-pass-labs-amp-combination-thiel-speakers-need-mr-pass-advice-everyone-5.html)

You can also get a preamp with higher gain so that you get more volume out of your system. c-j and Aesthetix preamps have gain in the 26 db range which is considered high, I believe, if you're interested in tubes. I don't think either has a phono preamp though.

If you're staying in Class A 90% of the time you are OK. Leaving Class A is not going to cause any harm. At 4 ohms you still have 240 watts of Class A/B headroom left when you leave Class A.

Some people feel that you need amps with a lot more power than what is required by your speakers to get the best sound. Others don't. If it sounds good to you, that's the main thing.

Did "...Nelson Pass explicitly recommend it over the other comparably priced amps in the line." for the Thiel CS 2.4's? Thiel suggests 100-400 Watts for the 4 Ohm nominal 3 Ohm minimum 87 dB/2.8V/m CS 2.4's.

As mentioned above, I was also pretty concerned about the power of the amp and was set on purchasing an X-250.5 for the Thiels. I eventually settled on the XA30.5 after seeing Nelson Pass explicitly recommend it over the other comparably priced amps in the line.

So far, the amp only moves out of class A at very high volumes, higher than I would use for about 90% of my listening... and still sounds very warm and sweet even when the needle starts bouncing.

As for the problem with the Classe, it's great and I love it, but unfortunately, it's obscuring some detail from my source components. I've got a PS Audio PerfectWave DAC and there is a lot more information in the system when I use it as a preamp and run it directly into the Pass. Alas, my girlfriend loves vinyl, so that's not a solution either.

Ohh, and for those offering solutions, my $2500 cap is for used equipment. I won't buy new.

Unless you think the amp is underpowered all the time, meaning that the needle is always moving... then don't you touch that amp! Kidding of course, but it's a fine amp and probably stays in Class A most of the time. Look into the W4S STP-SE preamp as it's fully balanced to match well with the XA30.5 plus it has a very low output impedance that will mate well with your amp. Alas, no phono stage, but you can get one of your choice, and still come in under budget.

I think you'll get better and cheaper results if you'll just use CAP151 which will make much more sense than your current Pass that underpowers your speakers. You can order a phono board from Classe and mount it yourself with easy instructions from manual. Child skill of Lego assembly experience is sufficient enough to do that.

Please forgive me for not answering your direct question, but I can't help but wonder if Cmalak is onto something. You might get more satisfaction from putting the money towards a higher powered amplifier.

Cal3713...is the XA30.5 capable of driving the 2.4s without any problems? No tonal abberations or soundstage collapse at higher volumes?

In any case, as for preamp suggestions, when you say your CAP-151 is being outclassed, how so? What are you noticing that you would like to change (more tonal density/texture, more resolution, more PRaT, more bass articulation/heft...)? Just trying to understand what it is you are trying to change or improve upon to tailor recommendations. I am assuming you are willing to consider used as well. Thx